Saturday, February 28, 2009

Tuning

I made a bunch of pictures to try and show how the tuning works, and I decided if one picture is worth a thousand words, one video is worth thousands of pictures (in fact that is literally true at 30 fps).

This is my first attempt at blogging so I'm in the fly by the seat of your pants mode. I needed a good graphics editor and came up with GIMP. I needed a better way to manage screen captures and came up with Gadwin Print Screen. I decided to see what I could do about some way to capture video from the screen and came up with CamStudio. All of these programs are freeware or under GPL license, the same as PowerSDR. If you scroll about half way down the PowerSDR page you will find the program and its associated drivers and manuals etc. This is the actual power in how Flex has developed its business model. By GPL-ing the software it is now open to everyone to advance the state of the art. I would not be writing this blog if the barrier to providing content was too high. If I couldn't get under the hood of PowerSDR a little it would be just another black box with a DO NOT ENTER sign, like the rest of the ham radio manufacturers. This is an interest of mine and I gain nothing except gratification that I can share some of my excitement of the SDR experience. It is the same for the amateurs who are every day improving PowerSDR in a collegial and cooperative community. If there was not a company (flex) there at the same time, as interest waned progress would stop. So like Google and its Symbiotes, Flex and its Symbiotes exist to nourish each other and the greater community at large by providing long term stability for intellectual processing to come to fruition. ( No I ain't no commie, I'm an old time systems engineer and this is one hell of a beautiful system) It is a variation of this business model that brought Google from an idea to a mighty internet presence. This model is a model that leverages intelligence, and that is way powerful. It is Google that owns blogger, and the servers upon which my whole blogging enterprise resides. We all gain when people come together in collegial cooperation. It is for that reason I want to thank the above software publishers and providers for making it easy for me to enjoy the fruit of my labor. I will write something about Flex's business model and the community is has generated in the future. It is something entirely differnt in the way Ham radio is done and is worth comment. Yes dare I say it...the Flex business model is still another dimension :P

On to tuning:

Here is a video of the PowerSDR console. I didn't "film" the entire console because the more area the bigger the file and the bigger the file the more herky jerky the quality so I settled for the minimum size that did justice to the topic

The script I followed is

screen

hand

vfo a

turn on split

yellow cursor

turn on multi

red cursor

vfo b

change filters

tune step

type freq

save- restore

zoom

pan

center

tx switch vfo

If you click TUNING .TXT you will get a new window with this list in it so you can follow along with the video. As I make changes on the screen it is useful to occasionally glance up to the VFO readouts so you can see how the frequency changes with screen clicks.





Here is a screen shot to compare




The video took over an hour to upload and render a 75mb .avi file. I had the thing nice and big and optimized, and blogger cut me down to size and turned me into a flash file so this is the best I can do given my level of expertise (laughing: what expertise). I use Firefox as my browser and Firefox allows the page to be magnified so you can actually bring the size up to something fairly useful to view. I'm sure other browsers have some kind of similar means to enlarge what is in the browser. There is a way to narrate this in audio but I don't have all day to spend on this so I will leave that exercise to another day. In the mean time if you want sound you can listen here (in honor of Texas!!!!)

When I taught Physics I used to open up my first lecture with a pair of Bose 901 speakers, a big assed Harmon Karden Amp in the front of the lecture hall, and this ZZ top tune blasting. It was sooo much fun watching about 250 jaws drop when I dropped the needle of the turntable (remember them?) into the groove. Man those 901's sounded incredible when mixed with the acoustics of that lecture hall. The 901's were made to be a rear fire speaker with a front fire tweeter, but I just spun those suckers 180 degrees and let er rip. We rocked old Albert Einstein in his grave!!!! Hell "Dr. Dean of the Science Faculty" acoustics IS physics it WAS relevant...

What you see first is the screen. Next I left click some portion of the screen and a little hand comes up that allows me to drag the screen. I can drag fast or slow and center my signal. Next I move up to VFO-A and use the wheel on the mouse to move the frequency around. I can move any digit so I can tune in 1's, 10's, 100's, khz or mhz as I move up the decimal tree. Next I hit split and notice that my VFO-B is on 40M, so I hit A>B on the console and that fires the contenst of A into B. I next turn on the yellow cursor by right clicking the moue. The right click runs you through a toggle sequence: "yellow cursor, red cursor, hand" Yellow cursor is point and shoot for VFO-A. Red cursor is point and shoot for VFO-B, and HAND allows for rapid excursion up and down as I described before. The toggle runs in a circle so when you right click its YRH YRH YRH. It is very intuitive. With the yellow cursor active I do some point and shootin on various signals on the band. PowerSDR has a feature called "Zero Beat" I listen to typically a 350hz beat note on CW. You can set this to what ever freq you like but for narrow filters (I usually run 100hz) a little lower beat note seems allow my brain to dig them out of the noise a little better. If you click tune to lets say a 500hz note, you can pop right on freq by clicking Zero Beat. The Flex allows filters as narrow as 11hz and you have to be a real dead eye to center an 11hz signal in the passband, so I just Zero Beat!!!!

Next I turn on the watch receiver by clicking MultiRX. The watch receiver is a second software receiver that pops up and gives you dual receive. It can be anywhere in the pass band of the display eg if you are sampling 96khz it can be anywhere in the 96khz window. It is NOT the same as RX2, which is a separate hardware based receiver. When RX2 is turned on it takes control of the VFO-B display, but I digress.... The watch RX is the same bandwidth as your main RX. There are controls that allow you to pan the 2 receivers in the stereo space in your headphones and you can adjust the volume of each receiver so you can have the pile up loud in one ear, the DX soft in the other as you look for the tail end freq. You can see the dance and hear the dance of DX and pileup, beautiful. You can adjust the watch RX freq by changing the digits in VFO-B or you can right click into the RED cursor and just point and shoot the pass band of the watch RX around in frequency, up and down the pile up, as I said listening to the stereo signals it produces in your head.

Next I change band width from 100hz to 1khz and do a little more point and shootin. Tuning steps are adjustable in the center part between VFO's you can also lock the vfo or you can sync the vfo's for dual diversity. You have step control from 1 hz to 10 mhz. This changes the sensitivity of how much each click of the center wheel on the mouse changes frequency. (this is the Flex equivilent of a knob. If you want something to actually grab and turn Flex offers some KNOBS as well. I am so over knobs. Mine sits in a drawer in the desk.) I usually run 10hz resolution. You can click the VFO box and highlight the numbers and enter a freq from the keyboard if you want a quick excursion to listen to some SWBC station you just read about (the radio does DRM out of the box). You can click SAVE and that saves the VFO A contents so you can tune around and instantly RESTORE that frequency, useful if you are waiting for a DX station to build his propagation for example

There is a ZOOM feature next which allows you to expand or contract what is on the screen and a PAN feature that allows you to zip up and down the band without messing with the frequency you are tuned on, and a CENTER control, to bring you back to earth in one piece.

Finally you can change TX freq between VFO A and VFO B by clicking the TX button at the bottom of each VFO. If you turn on SO2R the transmitter freq is displayed in the window next to the TX button on VFO A and you have complete control over the frequency of all 3 processes RX1, RX2, and TX which all run in simultaneous TRIPLEX....WAY COOL....

I hope I haven't bored you to death. The video didn't turn out quite as spectacular as I wanted and I don't have the bandwidth on my server to host this much streaming data in the better format. The video I did shoot is fabulous. The technology of collaboration is totally amazing. Last week I didn't know how to blog, and I had made about 5 screen shots in my entire life and only doodled with graphics software mostly for resizing picture from my camera. This morning I didn't know the HTML code to force a new browser. I had not clue one how to make a video. By the afternoon I had Googled my way into the future, on my own, for free, and had a total blast doing it. PowerSDR is another example of collaboration that is propelling us into the future. There is some dorky 160 phone DX contest going on this weekend, so I'm not missing anything on the bands anyway. I hope your weekend is as much fun!!!!

73

Can you guess who's guts are shown here?

Friday, February 27, 2009

Audio 2

Since we are talking audio, I thought I would take a look at how the display works both in monitoring audio and monitoring transmitted audio and a little bit about how frequency selection works. Many Many pictures because I know you don't want to read that many words

Here is the normal display I watch (you've seen it a million times)


What is here is a Freq v Amplitude display of the what ever bandwidth I am sampling. The F5K has 3 choices of sample rates, 48K, 96k and 192k. My preference is 96k. At that rate I get good processing speed as well as good processing depth. Everything in life is a trade off and at 48 you get really fine signal definition but increased "lag" in how fast the buffers empty out, and at 192K its just the opposite. With a good dual core computer (you don't NEED the best, you can buy a perfectly good board for running this radio here including processor, add a dab of memory a HD, an OS and firewire card and BOOM your good to go for under $300. N4HY has one of these going with about 50 different O/S 's and is very happy with its performance) The differences aren't great along the continuum from 48 to 192 as far as performance goes, so you pays yer money and makes yer choices. Also on this display is the red line which is my center freq 3772.000, and where in the spectrum I am listening the green. It represents a filter that is 2.7khz wide and that filter starts on the low side 150hz below 3772.000 and ends 2850hz below 3772.000, so this is a 2.7khz LSB filter, and that is what is coming into my headphones. The display is linearly calibrated in dBm and the radio self calibrates to S-9 = -73 dBm. This is a real true S-9 (I have shot a real true S9 into the antenna and came up with -73) and the S units are real true 6dB increments and the difference between S-7 and S-9 is the same as the difference between S-2 and S-4, i.e no compression in the AGC. DB over S9 are true dBm above -73 dBm. Its amazing how your perspective changes when you have a lab grade receiver. I have only seen a +40 over 9 signal once on this radio, and I have good antennas. Even the powerhouse stations tend to be below +20 over. What this means is all my other radios had terrible AGC linearity. And now I have man's best AGC. In effect it has put to rest for me all the hubbub about IP3 and dynamic range. I have plenty of headroom more than I need by at least 40 dB. I have fed signals as strong as +2 dbM into the radio in the filter pass band and not had the RX crap on me. +2 dBm is a true +75 dB over S9, and that's one hell of a signal. I had Klaus DK7XL help me check this in his lab this week just to make sure I'm not nuts (I have old HP equipment), and he had the same result.

Here is a spectrogram of noise on 75M during the day time



Not much to say, looks like 2.7khz of 75 M noise, but I could also look at RX signals


Here is what WWV at 10mhz looks like in a 16khz DSB filter.

Here is a shot of the scope using the same 16khz WWV DSB signal


The left is the carrier and the right is the carrier with modulation. Here is what the scope looks like on SSB TX on 3772

Yours truly repeatedly croaking OLA OLA with the compander ON. You see this sucker works on RX AND TX

The next screen is phase:


This is what the I/Q looks like when you say OLA, and this is what it looks like when you have just a carrier:



That partial circle of dots actually traces out a circle when going through the entire I/Q sequence. I grabbed about 90 degrees of data. This screen tells you if you have hardware problems. If it's not a circle (i.e. ellipse, box, pic of a Sommer beam or whatever) with a flat carrier then IQ are goofed up. (and Pi are round)

I know this is starting to seem like "how I spent my summer vacation" but it will get a little more interesting in a few slides

Here is the requisite water fall for all you digital freaks. The narrow part is what OLA looks like on transmit on SSB and the rest is a waterfall full of noise:


This pic is kind of pretty, reminds me of a Florida lightening storm. I don't run the digital modes else wise I would put up some diddle diddle diddle for you. Here is a cool one:


This is OLA on the histogram. The histogram is like the band scope with personality. It has hysteresis and a real time component, so you can compare where you have been and where you are now. Blue and red are realtime (as in post OLA) and green is the hysteresis during the peak was of the OLA (i.e max power out). You can see the shape of my transmitted signal with a little up-slope in the lows and little degradation in the middle and a little peak again toward the high end then a tail off since I sound like a bullfrog and I am not accentuating very high freqs. If you look at how I have my graphic equalizer set up, it looks just like this. On RX you get the coolest undulating display..... In a dark shack you might put on some Hendrix... Purple haze all in my brain... dum dum dum dum da da dee, da da dee, da da dee.... Lava lamps, who needs em....I got a F5K!!!

Here's WWV "at the tone":


Now: "'scuse me while I kiss the sky..."

Here are a series of dual shots where you can have 2 things on the screen at once;

First panadapter and waterfall:


Then Panadpater and Scope (OLA OLA OLA)



And finally panadpter with TX filter AND RX filter displayed

The green is the RX filter and the yellow lines are the TX filter which turns green on TX.

I was going to talk about the frequency selection methodology and how that is displayed but I think this is enough for today. As you can see, YOU CAN TRULY SEE, with this radio. Toss that old Heathkit band scope on the trash heap and git ya a Flex F5K. Its a very cool thing to KNOW you are not causing problems on the band at a glance. It is a very cool thing to be able to watch other stations and see what their signals look like. I know I'm wearing out the analogy but its a whole 'nother dimension. This is better than playing with your navel (or your knob) More on playing with the knob later.

Just for grins I captured some guy who is probably running a Yaesu and a keyboard clicking along at around 35 per:


You can see how wide his signal is, well beyond 100hz and in skimmer you can see the clicks on his signal (its that line at the bottom that looks like a bunch of H's. It should look like a bunch of -'s) Amazing!!! You can run but you can't hide from a Flex.

One thing I forgot to mention is there is a Quick Record and a Quick playback available on the front panel for recording and playing back audio clips. Qrecord records the audio stream to a .wav file that can be played back over a .wav player

73

Here is a little blurb Mr Audio W5GI sent me regarding his experience with the audio very interesting

The 3 band EQ was designed to work with professional studio microphones that typically have more low frequency response than communications type mics. If you hover over the words low, mid and high you’ll see the frequencies that each slider covers. For studio mic, one should use at least -9 db of Low cut. Typically it’s not necessary to adjust the mids or highs but if one does it is usually involves an increase or boost. The equalizer works hand in hand with the transmitter filter settings, which should also be viewed as a form of EQ, i.e. when one sets the low response to say 200, one effectively cuts out 200 hz of the audio response and therefore doesn’t have to cut the low end because the filter does so. Bob Heil did this with HC5 and HC4 elements; however, unlike the gentle roll-off of the Heil elements, adjusting the transmitter filter is brick wall and will result in more definite reduction in low or high frequency response. Another factor: the Transmitter DSP buffer setting will have a similar impact on the audio response. Try changing from 2048 to 512 and notice the shape of the filter when you are in transmit. Audio levels are critical in DSP radios. Typically one should see an average of 0db on the Transmit meter when it is in the MIC position. If one is to err, err on the minus side. The leveler in the DSP/ALC panel is another influence on audio quality-it should be used only by those with soft voices. The Mic preamp should only be used when one’s mic is insufficient to drive the radio to 0 db.Adding additional devices typically adds distortion. As you can see, there are a lot of features to use to one’s advantage or to screw things up.

The 10 band EQ is designed to international standards. A 10 band eq is difficult to get right, fortunately there are two tools that can be used to make its use worthwhile. You can use the monitor to listen to yourself ( you need low buffer rates and high sampling rates to minimize latency); one can typically hear the changes. A better method is to make a recording of one’s self and play it back making changes to suit the listener. Repeat the process as necessary.

thanks John!!!!

Thursday, February 26, 2009

Audio

In 1915 the phasing system of SSB generation was filed for patent. Below is an explanation of generating a SSB signal using the phasing method from the RSGB.

For this explanation, reference is made to figure A1. Diagrams (a) show two carriers A and B of the same frequency and phase, one of which is modulated in a balanced modulator by an audio tone to produce contra-rotating sidebands A1 and A2, and the other modulated by a 90 degrees phase shifted version of the same audio tone. This produces sidebands B1 and B2 which have a 90 degree phase relationship with their A counterparts. The carrier vector is shown dotted since the carrier is absent from the output of the balanced modulators. Figure A1(b) shows the vector relationship if the carrier B is shifted in phase by 90 degrees and figure A1(c) shows the addition of these two signals. It is evident that sidebands A2 and B2 are in anti-phase and therefore cancel whereas A1 and B1 are in phase and additive. The result is that single sideboard is produced by this process.



Figure A1 - Phasing System Vectors
(From RSGB Radio Communications Handbook)

B1 and A1 are additive vectors and B2 and A2 are opposite B1 plus A1 = SSB and B2 and A2 cancel. Note A and B are 90 degrees out of phase..... Wait a minute those are wiggling vectors AND they are 90 degrees out of phase... Where have I seen this before???? Could this be I/Q? This kind of signal generation is quadrature in nature. My first SSB rig was the HT-37. It was a phasing rig and I got rave reviews on the audio. You could crank up the gain and the thing would buck shot all over the band, but when you tamed it down the audio was fantastic. I called it WIDE BAND SIDE BAND W2OY hated it.

The F5K is just such a rig, a rig based in the phasing method of sideband generation. In the HT-37 the 90 degree shifts were accomplished in components and were not entirely linear, but in the F5K the shifts are accomplished in software and the phasing is perfect. I used to be able to get maybe 25 or 30 dB of cancellation with the HT-37. In the F5K you just set all vector values of A2 and B2 to zero. Now that's what I call cancellation!!! No sneaking up on it with little phase shifts, just BANG you're Zero!! Old timers (alas I've become one, I used to look in the mirror and see Robert Redford now I see Captain Kangaroo) will remember the phasing days. When the Japanese transceivers came roaring on the scene all that big iron like the HT-37 or the Central Electronics 20A went the way of the dodo. The new rigs all used crystal filtering in sideband generation. Whenever you put an analogue filter in the line you add distortion because the filter has its own characteristic which get added or subtracted to the signal. When you just cancel things mathematically there is no added distortion, just one sideband goes away and the audio quality is preserved. The F5K also uses its brick wall filters with rejection better than 100dB to set the band width, so the F5K is very well behaved on SSB indeed. In fact the F5K according to some of my buddies even has a particularly clean and distinct note on CW. They can tell when its me tuning up just by the purity of my CW note. I was amazed when they told me that. Personally I'm more interested in the CW performance of the radio but the radio is so feature laden for high quality SSB it deserves some comment. The program gives you pristine control over how you sound.

The F5K (and the 3K) allow for balanced input mics like the broadcasters use or single ended mics typical of communications. The Mic I used on my SDR1K was a balanced output condenser mic and the mic I use presently on my F5K is the Ten Tec 708A dynamic mic. Both mics get rave reviews on the air. I'm not much into the quality audio scene as the quality of my voice is reminiscent of geese farts on a muggy day, but there is a group of dulcet aficionados (W5GI et al) that LOVES this radio for its audio, and whats the point of owning a radio if you don't love it? The balanced mic plugs into the back of the radio and the 8 pin TT mic plugs straight into the front. The 8 pin connector pin out is Yaesu. I went with the 708 because I like the goose neck and the PTT arrangement a.k.a. convenience.

Mic selection and audio output in the F5K is via the mixer screen




As you can see you can choose audio inputs, audio outputs, and set various levels on these devices so you get a smooth transition in the program when you make the switch. This means I can set up the balanced mic and the TT mic such that I don't have to reset the mic gain on the front console

This is a shot of the 3 band version of the graphic equalizer

And here is the ten band version

I'm simple and mostly a CW guy so I use the 3 band version. Interestingly enough the RX equalizer sometimes comes in very handy. On 40M in the midst of the Foreign Broadcast I have some times been able to make stations otherwise uncopyable into Q5 copy by adjusting this feature. The TX and RX equalizers can be tuned off and on from the front console in the SSB modes

This brings up another point. When you switch modes the console changes. Here is SSB:


And here is CW:

Notice the control changes in the bottom right screen near the center. In CW mode CW relevant controls are visible and in SSB, SSB relevant controls are available. The change is automatic. The filter bandwidth controls also change their range from very wide SSB filters down to very narrow CW filters. The filters themselves are continuously variable by right clicking the filter control for example I have one of my filters set to 100Hz under CW. I set this by right clicking the particular filter button I wanted to set to 100. The set up screen looks like this


My center freq on CW is offset by 350hz and this filter is 50 hz above and 50 hz below 350 hz. Each mode can have its own compliment of custom filters. This scheme is one of the contributions I added to this software, so customer input does get added to the mix. (Of course Eric is the one who coded the idea).

Compander and DX Compander. I must confess I don't know how these work at the present. I have a line into the maven (N4HY) who wrote the code, so when I know more you will know more. Suffice it to say these really bring up the average talk power but they do so with virtually no distortion and no increase in band width or splatter at all. I run my compander at 3. If you crank it up it starts to sound crappy, but it you run low mid range, at least with the mics I am using, it basically adds a wonderful presence or depth to the audio quality similar to how stereo amps that have a "presence" control bring out greater texture and detail in the music, at least that's how it sounds to me. DX compander is compander on steroids and I never use it. I have only one SSB DX contact in my log, and thousands on CW so you can easily see where my interests lay.

The Vox controls controls are readily apparent. You can set sensitivity but the delay is set up in one of the setup screens and to change that you have to dig down a couple of menus. The Vox is very good not too sensitive and its not clicking all the time.



You can set up multiple transmit profiles so you can have a custom: contest profile, ESSB profile, regular profile, make the coffee profile and DX screamer profile all set up in the drop down menu all selectable at a moments notice. You can do whatever blows your skirt up, and save it for later skirt blowing with this radio.

You can show the TX filter on the display under the RX filter so you can see if your TX bandwidth will offend someone up or down the band. How civilized.

In addition you can set up a gate mode, which is a noise gate where it takes a certain level of audio before the radio will send audio down the pipe. Very handy for when you have that 3cx10,000 cranked up for the Gator stakes. You remember the gator stakes don't you? WB8BFS would hold forth on 3895 and invite everyone to dump it in. The loudest station he could hear was the winner. If you ever heard of the amp supply LK-800 tny (3 - 3cx800's with a big honkin peter dalh transformer in a separate power supply box), that amp was built originally for WB8TNY by Amp Supply so Chad, who lived down the road from BEEFUS could win Gator Stakes. W4MPE, the PUKE of Paducah always kicked his butt. They didn't call him the puke for nothin'. Them big bottles glowing white hot always kicked them little squirrel nuts. Good old 75M, its tame today compared to the past. We had a lot of fun. (now I'm really sounding like a geezer)

Transmit bandwidth is set up in the setup screen. The transmit filter looks like this

This filter is set at a low end cut of 200hz and a high end cut of 3100hz for a bandwidth of 2900hz. The filter will only allow 3khz in SSB. You can see the brick wall nature of the filter. Ultimate rejection is down about 130 dBm. If some kilocycle cop comes carping about how "wide" your signal is, you can just email them a pic of your transmitted signal along with a polite "fix your friggin receiver!!!!" Slaughtering OO complaints is like shootin fish in a barrel.

In the upper right hand corner you can see the drop down of the things that can be monitored by the meter on TX:


Each of these parameters can be monitored and adjusted for optimum and each has some input on how the final transmitted signal sounds.

I have presented a lot of pictures for a reason, not to just hear myself blow, (though I do dearly love to hear myself blow). If you ignore my witty banter and just spend some time looking at the picture, including the things I have not mentioned you will come to understand a lot about this radio and how it is designed. The pictures give a lot of insight. You can combine that with the F5K manual and gain even more insight. This post is getting a little long and has a lot of info to digest, so I am going to do an Audio 2 to show case the various functions of the display Way cool stuff stay tuned....

73

Noise

I was listening to 160 this morning. I was listening to OA4TT run some JA's and any other takers. My band noise this morning was running about -120dBm and the OA4 was about ten dB above the noise perfectly Q5




All of a sudden I was greeted by this:


I occasionally get this noise, and it basically takes out anything in the pass band. It usually only lasts for a couple minutes, but during that couple minutes I'm screwed. I clicked on the NB and here is what I saw


Virtually all the noise was eliminated and my noise floor returned to -120dBm and the OA4 was perfectly readable again. So the radio has a noise blanker, what's the big deal?

The big deal is the noise blanking is done in software. The noise is eliminated, period. It does not leave clipped holes in the signal like an analogue noise blanker and it does not affect the AGC. There is no noise bleed through into the pass band at all, and virtually no distortion. The noise floor is not affected. It is absolutely amazing. The OA4 was running a +1 split on his pileup. During the course of my listening there were a couple of the wide band CW Yaesu rigs that started banging away at him with signals in the -60 dBm area (ten over 9). With the NB on there was absolutely NO AGC pumping or added distortion even with these loud wide signals tempting fate. Here is a real change in how ham radio is done, a noise blanker that truly just eliminates noise without adding additional spurious response. This is the difference between making a contact and no contact. I have never experienced a blanker that works so well. Because it has no "parts" in hardware and is totally mathematical its behavior is perfectly characterized. You may love your knob, but I love the absence of noise. Noise messes with my demeanor. It makes the radio experience go from fantastic to funky in a NY minute. To tell the truth with the advent of point and shoot tuning I ain't much on knobs either.

This brings up another promise as yet to be fulfilled, what about eliminating static? What if you place a "watch receiver" somewhere in the pass band that listens to just static, that gives you the information of what the static looks like. Suppose you invert that signal and add it to the signal you are listening to, such that the static in the signal is the exact opposite amplitude of the inverted static? You would cancel the static. Since SDR is not real time but a little bit behind real time (due to processing) you have the luxury to do this kind of manipulation in software that you could never do in hardware. This is not yet implemented, but all the pieces are present. Given how well the noise blanker works can a static blanker be far behind? Here I think is one place where the Flex approach to DSP shines. Let's say your legacy radio has DSP. The question is does it have enough DSP? Is there enough room in the DSP to keep adding and adding features? Is the DSP fast enough to accomplish something like a static blanker? Clearly if the DSP is your computer you have plenty of room and speed, and if you run out of room and speed its a simple matter to increase both parameters.

Signal are always present. If a VK is sending on 3505 at 12 in the afternoon his signal is present to my radio. The question is can I get far enough down in the noise to hear him. One day I did work a VK on 80M at 12:49 in the afternoon. In the summer we are limited in our DXing by static. Suppose you could eliminate the static. Take a look at the above pictures and imagine the possibility

UPDATE:

I captured said NOISE on audio and converted to an MP3 file I turn the blanker off and on several times

73

(note: the above is really only 2 pictures one with the noise and one after the noise was blanked. because of the way I do screen capture I have to dump clip board memory between screen captures which is kind of a curly shuffle. The before and after pics were the same so I just made 2 screen dumps for illustration, but the story is accurate)

Tuesday, February 24, 2009

Dual Diversity

I was calling my buddy Joe on 75 last night. While I was calling I had switched into basically what is the SO2R mode to listen on 160 CW, while I was plowing a hole on 75. I have ADD and I love to do 2 things at once. Here is a shot of the rig running on 2 bands at once. The 2nd RX is on my 160M antenna and the 1st RX is on my 80M open wire fed flattop through a Johnson KW matchbox. The 160M ant is about 80ft from the end of the dipole. I was running 1500W on the dipole. As you can see as far as RX 2 is concerned there is no problem running high power with antennas that close.




When I had my SDR-1000 set up with the Orion, I used the SDR as my DX radio and my Orion as my 75M rag chew radio. I also have another 80M vertical on another part of the property and would either use the flat top or the other vertical for ragchewing, and use the multiband vertical for DXing. With the SDR1K and the Orion I could run 1.5 kw on either rig and not tell the other rig was on the air except on the same band. If I was on 75, I could hear the Orion in the SDR down around 3510 at about S-1 and I could still work DX as long as they were above S-1 using the SDR while blabbing with my friends around 3772. I had the SDR-1000 set up for auto bandswitching of my antennas and I had a no tune amp in the line so it made working DX while shooting the bull with my buddies like catcing fish in a barrell. Point and shoot Bang you're dead. An ADDers nirvana.

I have a couple of N8LP's super fine verctor SWR bridges. The thing had just come out, and I figured out how to use the thing as a field strength device by turning the inputs and outputs around and feeding my antenna into a dummy load. This allowed me to measure accurately how much power was on one antenna while I was transmitting on the other, without any filters or anything getting in the way. The LP-100 is calibrated in DBm so it too was direct readout. I measured about +30 dBm on my vertical when transmitting 1500W on an antenna 80 ft from the vertical. This is what was presented to the input terminals of the SDR-1000. I felt pretty good about that. I could work -128 dBm signals on for example 40M while I had about 1 watt of 80M signal coming down the same pipe and as far as the SDR-1000 was concerned it didn't know I was on the air on the other band. WAYYYY COOL.

Joe and I were shooting the breeze mostly about the economy and how we got here. I actually feel pretty good about the economy. In my opinion this is the worst time to be in cash. Later we started talking DX. Joe had spent a lot of time trying to phase lock a couple of his radios together for true spatial diversity. The F5K with the 2nd RX will do that out of the box. I had never really tried that feature. Joe lives on a ridge top in a million pound stone house called: Stately Johnson Manner up in PA. When he looks east he looks at Europe. When he looks west he looks at JA. His QTH is not on "River Bottom Road". He lives up on: "Way the hell up in the sky" drive. Its an amazing place. On the Manner he has several beverages. A couple of his beverages are pointed at EU far enough apart to make diversity a rational question, and his experiments were to try and phase lock a couple of RX's to make that diversity happen. It was an interesting thing to think about. I don't have that kind of real estate so I didn't really consider it before.

After we signed I decided to give diversity a try. Here is a shot of the F5K set up for dual spatial diversity reception on 160. The station in my cross hairs is IV3PRK blasting away, CQing on CW. The set up is as follows, RX1 is connected to my 80M flat top since that is way I had that antenna configured using on RX1. On RX 2 is my 160M inv-L. The flat top is tuned for 80M. Luis is always strong at my QTH. Last night on my inv-L he was coming in as much as 25 to 30 dB over the noise which was down around -120 dBm. The signal on the 80M flat top (RX1) was considerably weaker due to the antenna and the tuner attenuation, peaking out at -115 to -120 dBm, with the noise down around 130 dBm. I chose this set up so you can see the difference in signals easily. I first tried looking at something on 80 but my 80M dipole is pretty close to my vertical in performance, so I'm not sure the difference would be as obvious. The QSB was definitely different on each antenna and I think it would make a difference. It was late and I needed sleep so I hung it up the night with visions of multi-dimensional QSB in my mind.

To set up the F5K in Diversity mode is easy. You choose the RX1 antenna and the RX2 antenna hit ALT-D and hit VFO sync, and you are there. RX1 and RX 2 both send signals into a stereo space if you are wearing headphones. You can pan either RX anywhere you want in that audio space and you can independently control the volume of each receiver. I could bring up RX 1 or RX 2 and move things around and Luis's CQing was all over my brain's spatial field. It was a lot of fun. I will have to give this a try on some DX sometime that is way down puny weak and see how this plays.

Here are a couple shots of the antenna switching menus. The antenna switch can either be in simple mode or expert mode. In simple mode you can choose what output goes with what antenna. If you are on antenna 3, the radio also can turn an amp that is connected to antenna 3's signal path off and on with transmit. This means if you have the alpha connected to antenna 1, and the Acom connected to antenna 3, when you are on antenna 3 only the Acom will switch to transmit when the radio switches to transmit. You can also determine what goes into RX2 and your choices are to tap to what ever antenna is connected to RX1, to a separate antenna or to Ant 1. In my example I had RX2 set to antenna 1, which is my vertical stack, and my dipole which was on the antenna 3 port was connected to RX1. There is also provision to stick a filter or a preamp in the RX line if you want to do some shaping to the RF prior to in getting to the Tayloe detector. You also have control over "delay". This will allow a bunch of relays to settle down before you transmit so you don't have to worry about blowing up that mast mounted preamp.


In expert mode you have pretty much the same conditions except you can make the choices per band. So for example if you have 160 beverages on the RX input you would likely not want this to be a choice if you were using the ten meter beam.


It's a very powerful switching system and gives you much more power than what I had with the Orion. I think it has great potential for a contest station because changing bands becomes point and shoot.

This is a shot of cross band operation. I know I know pretty mundane. This is one of the real difference between the F3K and the F5K. This is a feature set that is not available on the 3K. The 3 K will have "watch" receiver capability which means you will have 2 software receivers in the pass band of the panadapter, so working DX will be a breeze, but you won't be able to easily work cross band as it doesn't allow multiple antennas etc. I expect if you are using something like a multi-band vertical or a beam there would be some cross band possible, but not with the same flexibility as the F5K



Here is a shot of the program DDUTIL which is a program added to the flex family that adds a lot of functionality. It is written by Steve Nance K5FR. You can take a look at his WIKI to learn all about this program. This shot is of the band following feature of the program. It will send some data out a parallel cable to a switch box so you can have auto chosing of antennas etc. Also it will run your STEPPIR and point your rotor and band switch your Acom 2000 or your Alpha 87A or your Quadra. It has inputs to monitor the LP100 watt meter. Its main feature is you can have up to 4 programs address the F5K at one time. I have 3 set up at my QTH, N1MM DXlab and Skimmer. The software is being written so you will be able to address a whole slew of transvertes. So if you are a VHF UHF maniac this thing will allow basically complete station control over a big time multi-band VHF station. That part of the product is in beta testing right now. Its a very useful add on from someone who is in the Flex community and wanted to be able to develop integrated control for a bunch of his peripherals. THIS IS FLEXIBILITY. This system is fully integrated into PowerSDR even though it is not part of PowerSDR but a separate development. At some point I will write something on the Flex radio community and colaboration.


There is always some new aspect of this radio to explore. DDUTIL will provide for example a great deal of added functionality to the F3K once it is released, so its like getting an upgraded radio for free. No messy modules to add like some legacy radios.

This brings up one last point. If Joe had this radio, I would be able to access it from MY QTH and use HIS beverages way up there on nose bleed ridge, and of course he could use my about" spitting distance from the Atlantic Ocean" verticals at HIS QTH... Let that thought bubble around in your cerebral sauce pan for a minute.... What could you do with a high performance remote receiver????

73

Tuvalu #2

Interesting QSO, he was on 40M and people were working him simplex. No pileup at all. Very civilized. When my turn came, he was an easy one call pickup. He is an excellent DX operator. My band noise on 40 runs around -125 dBm and Mr Tuvalu was hitting -102 dBm. Not bad on a 7200 mile path.

I really like being able to measure signal strength directly in dBm, and I like the fact that what I see is linear across the S meter's range. I like being able to track my band noise. If my noise is high there isn't much point in even listening. I also like being able to see my noise. Sometimes noise is local across just s few khz and drifts up and down the band, and with the panadapter you can see instantly what's going on. You don't have to tune around to try and characterize the noise.

I was using my 1/2 wave end fed vertical, which is perhaps the best vertical I have ever built. I have a 1/4 wave 40 on another part of the property and this half waver doesn't do anything the 1/4 wave doesn't do, but it just seems to do what it does with more elegance. If I had the support height I'd make all my verticals 1/2 wave antennas, but by the time I got to 240 ft on 160, I'd be better off hanging dipoles off that tower for the bands above 160.

The other Tuvalu station T27A just came up on 160, but I don't have propagation yet. My band noise on 160 runs -118 dBm and grey line for me is still 30-40 minutes away. I'm sure my only chance to work him would be with grey line enhancement, so I won't get to hear (or work) him this morning, as duty calls and I'm already a couple minutes late. The DX cluster spotting station is up in New England. New England is already into its grey line enhancement. You think of Florida as very east, but its amazing how far west it really is.

73

Monday, February 23, 2009

Tuvalu

This morning as I was heading out the door for another hectic day of gas passing, I stopped by the shack for a quick listen. Tuvalu was coming through on 80. He was a good 10dB out of the noise, and the band was quiet so he was perfect Q5 copy. The F5K has 3 antenna outputs and I keep my AL80B on one of the outputs for just such an occasion. The Acom takes 3 minutes to warm up and the Alpha 2.5 mins. The AL80 on the other had is virtually instant-on and ready to go. Its tuning is very reproducible and I have some little arrows I made with a label maker for various quick tune occasions like this. I had been tuned on 160 earlier in the morning trying to bag a ZL that was working Brazil. I set the band switch, tune, and load and was ready to go in about 5 seconds with about 1000 watts into the wire.

It was early in the pileup and the station being worked was up about 1 khz. I did the FFF (frequency flip flop) by clicking <> on the F5K and then clicking the station being worked by the DX on skimmer and <> again. Usually this would set me up perfectly for a tail end, with Tuvalu in the RX register and the guy being worked in the TX register. On cue, I started banging away into the ether and then listened. Mr Tuvalu wasn't in tail end mode. He was working a guy about 100hz up the band. I watched the panadapter for a second and saw the pileup was beginning to build. I saw several Yaesus with their wide band CW banging away. If I didn't get him in the next couple of minutes I would have to hang it up for the day. Its eyeball day at the old salt mine and I had at least a dozen cataracts lined up for extraction and lens implant and I couldn't keep the folks waiting. I did the FFF again and proceeded to heat up the ionosphere. No go. He was working another guy100hz up the band. Next I heard him work my old buddy K3RR another 100 hz up the band. I set my trap, I did the FFF on Joe's freq and then advanced another couple hundred up the band into a quiet spot on the panadapter, and started banging away.

I sat down at 6:23 and by 6:31 I was backing my car out of my garage with the station secured and Mr Tuvalu in the log. The F5K and skimmer gave me a perfect and realtime understanding of this man's operating style. This radio is way TMF!!!!

73

Saturday, February 21, 2009

Verticals Radials and Lab Quality Receivers

A few years ago we had a horrible hurricane season. The first one through was Charlie, and he broke, one of my 100 year old oaks with a trunk 6 feet in diameter like a twig. It was a shame, that tree added at least 10,000 to the value of my property and cost me a grand to have removed, BUT it opened up some space in the back so instead of acorns I planted aluminum.

I started with Butternut HF-2V I had laying in the garage. Of course with verticals comes the constant conundrum, HOW MANY RADIALS. If you read the EHAM Elmers forum very much, that question is asked about twice a week. Radials are like prunes. Is 6 enough is 12 too many??? It all depends, AND like prunes, you need at least as many as you need, but you really don't need any more. You can read ON4UN 's book or a million other sources or try and gleen the goat entrails to answer this question. The argument on EHAM usually goes: "I got ten and I worked England!!!" Then some joker whips out the ARRL hand book and whacks you with it...120....120....120... 120 times. 120 probably comes from the FCC's proof of performance for AM broadcast stations. If you string 120 of the suckers, they won't make you do a full proof of performance, which is a real PITA. Hams are not responsible for proof. Hell we're just amateurs. Like girls, when the working day is done, we just wanna have fun.

The real gold standard of how a vertical performs is to measure its field strength. It really has nothing much to do with impedance bridges or SWR's. Those things may be strongly or weakly correlated with performance, but what wiggles the other guy's S-meter is field strength. I planted about 12 radials as the Butternut manual suggests and promptly worked England on 80. I had a lot of fun that winter making contacts. I worked DXCC on 80 in about 3 weeks. But I was always bugged by the prunes question. Over the course of that winter I aquired my SDR-1000.

The SDR-1000 has a wonderful receiver. The AGC is dead on accurate with no over shoot, and the RX is absolutely"linear" (if you can call something logarithmic "linear") in the way it reads. It reads out in dBm from MDS (-135dBm) till the RX runs out of head room somewhere around +2 dBm (73db over S9), one measly dBm at at time. This is a true 73 db over S9. Most radios would have folded long ago. Signals that would run 40 over on most radios (because of their poor linearity) usually only run S9 to 10 over on this radio, meaning there is a whole lot of head room up there. It also runs off 12V as in car battery, and the "sound card" can run off the fire wire port without an external power supply. So I took a laptop and the SDR-1000 and hooked it up to my car and parked my car at the front corner of my property and flipped a little wire up in a tree. The laptop was connected through my LAN and I had another laptop at the base of my vertical also connected to my LAN. With TightVNC, I was able to control the rig in the car from the base of the antenna and I could record dBm as I fiddled with the antenna. I put a signal gen on the antenna and tuned the RX to that freq.

I had a ground rod at the base of the vertical and started my measurement there. As I added radials I noticed that when I connected the ground rod to the radials my field strength went DOWN. What the heck was going on???? I expected my strength to go up. I added wire and added wire and eventually around 25 wires when I connected the ground rod there was no difference in field strength. I added another 15 radials just to see if there was any difference. At 25 radials my base impedance also stabilized and the addition of more radials really didn't change the base impedance or SWR bandwidth. I say this as a conformation test and not as the major thing that was being measured which was field strength.

Here is what I discovered. A vertical pipe when excited with RF induces fields into the ground and it is the point of this radial field to recover these currents and return them to the other side of the coax. What you want is a really low common mode impedance between ground and the coax. It is my impression the radial field acts as the top plate of a capacitor, and the earth acts as the dielectric and bottom plate. As you add radials you effectively couple into the ground. Once you are completely coupled into the ground no more coupling makes any difference. I think the reason I saw a decrease of field strength when I attached the ground rod is because that made a current divider when part of the current in the radial field was shunted back into the ground, and part went to the coax shield. As the radials increased eventually there was no longer a potential difference between the rod and the radial field. Both were effectively at "ground" potential, and all the current was arriving at the shield of the coax. ("All" of course is a relative term, but in terms of dBm any additional return was asymptotic) I had my low impedance common mode path between the coax and the currents that the monopole was inducing into the ground.

As a first iteration before I went the SDR route, I tried using my Elecraft K-1 as a detector. Unsatisfactory. ACG and S meter were not accurate enough, and too much running around between the car and the antenna. The lab quality RX in the SDR and networking ability made collecting this data possible since I could visualize what was going on quite easily. Later I put up a full size vertical on 80, and I tested again. This time I parked my car on my buddy's yard about 3 blocks away. I put up a 10ft probe antenna hanging off a branch of a tree using the car as the counterpoise, and I used a WIFI tin can wave guide antenna pointed to my QTH. At my QTH I had a WIFI repeater on a tripod connected to another waveguide antenna up on the roof of my garage. I wanted to see if there was much difference being close to 10 wavelengths away instead of 2 using the big antenna, plus I wanted to screw around with long distance wifi. The radial field was about the same under the big antenna. At 25 radials there wasn't much change and I really couldn't tell if there was a difference between 2 and 10 wavelengths because the 66ft pipe is a better antenna, and I didn't have the HF-2V up anymore. The bandwidth of the big vertical was dramatically larger than the short and my impression is that the antenna is more efficient. Maybe one day I will give that experiment a try between the car parked in the front yard and over at my friends house. The new F1.5 K should be perfect for that test.

I'm not suggesting 25 is enough. I am suggesting 25 is enough for me given my soil conditions. I use this radial field for multiple verticals, the 80M 1/4 wave, a 40M end fed half wave, and a 20M 5/8 wave, plus an inv-L on 160. I use the 80M antenna on 30. I use a relay box to switch antennas and find virtually no interaction between the 4 antennas. I later added some 120ft radials after I added 160, just because I could, but I didn't take the time to do any 160 measuring. 4 verticals, 5 bands, one pipe, and one radial field I love it when a plan comes together.

So here is an example of how the SDR-1000 was able to be used as a remote lab quality receiver helped me answer the age old conundrum, and gave me the chance to spend some time out in the yard having some very interesting spring time radio fun. What's the difference between 25 radials and 120? In my case a lot more money and a hell of a lot of work and really no more signal wiggling the guys S meter on the other side of the world. I've put in several 120 radial fields before and its a project.

One afternoon as I was running these tests I walked into the shack about 12:45 local and did some tuning up using the amp on the low end of 80. Low and behold I was called by VK6HD at 1 friggin o'clock on a hot Florida spring afternoon. I was floored. He was perfectly Q5 and the only signal on the band. He confirmed. What a hoot!!!

73

F3K update (and other ramblings)

I was at Orlando and had a chat with Gerald. The new F3K was displayed, what a cute little radio. Its about the size of a laptop, 100W with built in antenna tuner. Of course the talk turned to performance. The radio is in beta production, just barely, so there aren't a great number of units available, but at least one unit at that time had been put through the numbers ringer. One of the beta testers (one smart cookie and a friend of mine) has agreed to guest a review of his "out of the box to operating" experience on the blog. So those of you interested in the new radio should stay tuned.

Dynamic range on that radio was apparently in the low 90's. Gerald would not commit to a number but it clearly is above 90. I heard yic yak of 94 but don't quote me or them on that, it's just what I heard. I'm sure they want to test more radios before they commit to a number. Gerald was very clear he expects in the "low 90's". At what spacing? The Flex radio is independent of roofing filters for its performance, so the spacing can be 50hz as far as this architecture is concerned, as long as the signals in the pass band have the kind of purity such that, the 2 transmitted signals would not mix with each other due to other than transmitter crud. You could never use a couple of Yaesu's to perform this test. In other words if you have pure enough test equipment the SDR is capable of dealing with the load. 94dB would put it even with the two Orions (man's best radio from a couple of years ago) in Sherwood's list. That 94 dB would be good at 100hz or 10khz. It is independent of the "roofing filter".

The F5K is in the 100dB range, and is not phase limited.

The reason I bring this up is:

1. It's exciting

2. The introductory offer of $1499 expires on 2/28 so if you have any expectation to try a Flex radio this is a most bang for the buck offer.

I already have mine on order for just these 2 reasons.

There is also the F1.5K which is coming out later in the fall. This has been upgraded to a 5 watt radio from a 1 watt radio, with an RX capable from 11khz to 60mhz and ham band transmitting from 160 to 6. It will have a 48khz panadapter and operate through a USB cable. The intro price is $499. Lemme see: (put finger on chin and eyes looking up to the ceiling) put a 50 buck laptop and this sucker on the back 40 where all the beverages or that quad of W8JI rx 4 squares are located, and wifi back to the ham shack as a remote RX. The software and hardware to remotely control the relays for that brace of 4 squares, from software (ddutil) is in beta testing as we "speak". You will pay for this set up in saved cable cost alone, and you can run it off a battery and solar cell. I have a buddy K4ESE who is looking into just this situation. Its easy to set up WIFI to cover even a few miles if you can "see" the remote site. I've done over a mile down an open road, and 3 blocks through the trees. I have done remote operation of my SDR-1000 using tight VNC as the remote protocol between a Linux box and a windows box over wifi, and using something like Skype to do the audio duties. I was able to make CW and SSB contacts using the keyboard and mic in the remote computer using this set up. I was also able to start all my favorite ancillary software like Skimmer and DXlab. The setup was on my LAN but there would be no problem sending that through the firewall if I wanted. Hey Baby welcome to the future!!!

The Flex software is being rewritten. The new software is expected to be platform independent AND distributed, so you can have the back end, the end that does the DSP on the remote laptop for example, and put the front end, the end that has the panadapter and controls etc on your station's console. Each button on the present software has associated with it a lot of code. The new software will have the buttons connected basically to a bunch of links, and operate more like a browser in a server client configuration. My remote setup was fairly crude and there was a lot of overhead required to connect the 2 computers, but the new software should make things much more integrated and transparent, sexy and svelte. What this also means is you can run a Linux box with its decreased overhead at the radio, and run a PC in the shack so you can have all the PC related third party software like logging programs or PSK programs that you want to run to have your radio fun, and after all this is all about having some radio fun.

This brings up a question how much is enough? If I have a radio that will do 150dB dynamic range is that any better than a radio that will do 95? I'm sure there are certain fairly artificial conditions that might require a 150dB dynamic range, but does my station ever encounter something that needs 150dB? I corresponded with a ham from the northeast that was involved in some contest effort where the station had something like a 4 el 40M quad (bet that sucker is hard to keep up in the winter), and with that antenna SWBC was apparently an issue on some radios. I'm trying to acquire some data from some European Flex owners to see what it is like on 40M in places like Germany. I figure the best way to look into this is to go to the horses mouth. Its an interesting question. I have a car that will do 155mph before the computer shuts it off. It's got a fancy tuned up chassis, 19" wheels, and is a lot of fun to drive, but I haven't found a venue yet where I can go 155 and not be begging to be killed by some rat carcass in the road. How much is enough? Are we there yet?

73

Thursday, February 19, 2009

IMD??? What IMD

The theme song from the Soprano's goes, "woke up this morning got a blue moon, got a blue moon in your eyes." When the lead singer in A3 sings it however it sounds like "woke up this morning got a boom boom, got a boom boom in your eye", and that kind of fits with the Soprano's theme. It also fits with this theme, because the data I'm about to present, though not definitive should expose precisely how the ARRL testing methodology has held back Ham radio. Hopefully it will put a boom boom in that eye.

The ARRL test originally put 2 strong signals in the passband of a receiver. The idea was to increase the amplitued of the signals until distortion occurred. From that you could graphically determine the imaginary IP3 of the radio. The test was jiggered form the start. They measured from S-5 to distortion, which tended to over state the IP3. Most radios of that era were up conversion radios, that is the 1st mixer ran with synthesizer way above 30 mhz, and that was mixed with the HF spectrum and gave a continuous representation of the1.8-30mhz spectrum that was presented to the IF filters. The 1st IF was then down converted again to around 455khz and then demodulated to audio. This gave a nice way to shift the 2 filters against each other giving a kind of continuous band pass tuning. The first mixer was in the 45 mhz range.

Ten Tec however designed the Omni-6 with the first IF in the 9mhz region. The radio was known for its strong signal handling and its clean VFO because it did not have to contend with phase noise from the synthesizer, crudding up the pass band. The engineers at TT got a wild idea. Instead of just one wide filter in the 9mhz region they expanded that to multiple filters. This was the birth of the "roofing filter" It was basically impossible to design a filter at 45 mhz that could do the job of 8 or 10 poles at 9 mhz. This meant the TT radio became even stronger. It basically was a radio that was custom made to pass the ARRL test. If the test spacing was 20khz you would have an incredibly high IP3 compared to radios that overloaded in the upper IF region, because they did not have the advantage of the "roofing filter". The name of that radio was the Orion. TT banged the heck out of that in their advertising and I can't say as I blame them. The Orion is basically the Omni-6 taken to its end. It is part Omni-6 and part digital radio. I won't go as far as to call it an SDR, at least in the Flex radio sense, but I will call it a FDR. Firmware defined radio. It had some flexibility in its design but to get new functionality you had to download proprietary firmware and flash the radio. This worked OK until the processor inside the radio ran out of memory. Basically at that point the radio was fixed in stone.

It still was and is a very strong radio however. What the Omni-6 lacked in features the Orion delivered, AND it still had that roofing filter that gave it super strong numbers on the ARRL test. Best in the business at the time. Next came the Orion-II which was the Orion with little more memory in the processor and narrower roofing filters. Then came the K-3. The Orion suffered from some quirkiness, and Elecraft set out to do the Orion right. They have the basic roofing filter design of the Omni-6 plus a much better derivation of the FDR, and the radio is modular so you can make it as basic or deluxe as the feature set allows, keeping with Elecraft's peddling of the old Heathkit model of selling kit radios that gave the "builder" the experience of being some kind of wild and woolly home brewer. What a wonderful marketing ploy. I used to read the Elecraft reflector and it was amazing how many posts I saw "Its Alive" as some builder completed his K-2 following the directions and lit it up and it worked. That is not to take away from their fun, its just to note if you build a kit according to the instruction it will probably work. The new radio is more complex and Elecraft made this radio modular so there is still that kind of "feel" of being wild and woolly. The K-3 has some really good numbers on the ARRL testing methodology. It has good numbers because it has roofing filters down to 200hz, and once again if you put one signal in the pass band and one signal out of the pass band, that knocks the mixing products way down not much mixing will occur. So this radio was not only made for the test, but the test was made for it. A marriage made in ham radio heaven.

So the question, what happens when you put 2 signals INSIDE the pass band? If you read my previous posting regarding the 160 contest you will recall I was working signals 40hz apart with multiple other signals of S9+ all within maybe 150hz of those 2 signals. In other words all the signals were INSIDE the pass band where the "roofing filter" couldn't jigger the results.

Here are some picture of some testing that was done and published on the CQHAM forum site. CQHAM is a Russian ham radio magazine or web-zine or what ever. I can't vouch for exactly how these tests were run, but from what I can tell looking at the pictures, 4 modern high buck radios were tested. What was looked at was the linearity of the in-band filter response with no signal, and how the radios respond to 2 strong signals INSIDE the pass band, not protected by the "roofing filter" The 2 pics with the signals appear to be one with the preamp on and one with the preamp off.

Here is the pic of the passband:

IMD-passband no signal



Note the brick wall filters exhibited by the F5K, and the lack of mixing products. Note the mixing products in the K-3 pass band even without signals present. My guess is these signals were moved up and down on the screen of the analyzer so the differences in the pass bands and stop bands could be easily discerned.


IMD-2 close spaced strong signals no preamp

One pic is worth a thousand words. The F5K has virtually no mixing even with S9+50 signals only 300 hz apart, and the pass band remains flat. There is no added energy or non linearity that gives the pass band a "bowed" appearance. This is a good example of why the F5K is so quiet on RX.

IMD-preamp on

OMG!!!! the bottom has dropped out of the K-3, often hawked as MBR (man's best radio!!!!) and now you see the fallacy of the ARRL testing methodology. If you stuck that s9+50 signal OUTSIDE the roofing filter you would probably have something closer to the first picture, but when 2 signals are competing INSIDE the pass band, the RX folds up. Look also at the F5K. You can work stations all the way down to MDS (minimum discernible signal) which is on the order of -140 dBm. This is my experience of the SDR-1000 vs. the Orion, and why the Orion went in the ditch when it was subjected to multiple S9++ signals competing with puny weak noise hugging DX signals in my contest experience. Note also how flat the pass band is in the F5K. I believe this is largely due to crud in the radio from the non linearity of the various multiple hardware stages in the legacy radios. The F5K on the other had is direct conversion and does all its magic in software via equations and not components, and as such the F5K represents a crud free zone.

My experience of the F5K is like this as well. I can get right next to any CW station, and as long as that station does not violate my pass band with clix or some other garbage, I have no trouble copying signals at the noise. 20 or 30 hz separation is more than enough. I have never experienced any blocking on the radio. It does not mean it can't be done but at least I haven't had the experience. I can often filter out stations that call on the transmit freq of the DX in a pileup, and eliminate them completely with the filtering in the F5K. I can't get rid of them if they are zero beat, but if they are 30 or 40hz down the road they are toast. I can see the offending signal popping up strong as heck on the panadapter but they are not readable in the audio pass band.

So there you go. I don't have the exact testing conditions etc etc (I don't read Russian) but you can figure pretty much what is going on just by looking at the pictures. One thing for sure it does put the boom boom in the eye of the ARRL testing methodology, and this game played with roofing filters. If you can get F5K kind of in band performance in this simple kind of test, why does the ARRL not test like this? To me the answer is pretty obvious, but I'll leave you to make your own conclusions.

One thing of note however. If you "can" do F5K kind of performance is it this "test" that is holding back advancement of the state of the art? Is what is going on simply ham radio manufacturer after manufacturer making yet another iteration of a radio that is not designed for best performance but designed so it can claim bragging rights with high test results?

I used to teach Physics at the college level. Many of my students were the "pre-med" crowd. It was my distinct impression they were not interested a whit in physics, but they just wanted me to teach them to the test, because "they were going to med school". The reason it was my distinct impression is because I was told that more than once. Teaching to the test has left a bad taste in my mouth ever since. Teaching to the test NEVER will advance the state of knowledge, the same as jiggering the Ham radio tests will never advance the state of ham radio.

73

Wednesday, February 18, 2009

A Quick little riff on how SDR works

I was at the Orlando Hamfest last week end and as I was walking the aisles I saw Gerald K5SDR making a beeline for the forum pavilion. I guessed he was on the way for an SDR forum so I trailed him into the tent. Sure enough he unpacked his laptop for a PowerPoint presentation. I conned him out of a few diagrams from that talk so I could give my layman's view on how to think about SDR.

Here is a modified image from that talk: (click pic for bigger)



What you see is basically a block diagram of the SDR-1000. The RF comes in the antenna, goes through some passive band pass filtering and into a QSD (quadrature sampling detector). This is basically a mixer. Mixers multiply and what you get is the two signals (VFO and RF) added and the two signals subtracted from each other. This is a direct conversion receiver. RF goes in, and audio comes out. It is a very wide-band audio, but none the less its audio. This audio is called the base-band. You can vary the frequency of what part of the RF spectrum is demodulated by the VFO, which in this case is a DDS or direct digital synthesizer. The DDS is the thing that allows for the spectacular point and shoot tuning method.

What comes out of the QSD is a special kind of audio. Its called I/Q or quadrature. and it is a digital stream instead of an analogue stream. A little digression is needed.

Most of us took a little grade school math and we learned this formula C^2=A^2 + B^2. This is the theorem of Pythagoras, who lived around 500 B.C. What he found is that if you know 2 sides of a right triangle, you can figure out the third.

If you know the frequency, and I and Q, and you sample enough data points you have enough information to completely characterize an analogue signal from this data. Here is a pictorial of how the QSD works:

You will note that RF comes into a switch. The switch rotates between one of 4 capacitors. As the switch rotates it imparts a voltage on the capacitor. That voltage is fed to an amplifier that has + and - inputs in other words 180 degrees out of phase. This gives you the data points, each with a voltage (what ever voltage is coming from the antenna) and a phase 0, 90, 180 , 270. If you know the frequency you then can sample enough information to be able to exactly reproduce the information contained in the RF signal. Basically this is a mixer. Once you have the data points, you send them into the computer via the A/D converter. The SDR-1000 used a "sound card" The sound card has an A/D converter and this is how the data arrives in the computer's memory. The F5K doesn't have a "sound card" per say, but just a very high performance A/D with a high dynamic range

Once in memory the actual DSP digital signal processing takes place. In other words it is the COMPUTER and some components of the PowerSDR software that is the DSP, NOT the sound card, and this is the true power of the Flex Radio approach to DSP.

If you look at the above daigram of the SDR-1000 you will note I have divided the diagram into 2 parts. Loosely speaking you can think of this radio as a dual conversion radio. The first conversion is the Analogue/Hardware portion of the radio. The second conversion is everything south of the A/D converter called Digital/Software. The hardware conversion relies on the very strong signal handling capability of a direct conversion receiver. One great advantage of this kind of receiver is how little distortion is added to signals. It's like the quality of crystal radio, crystal clear. As you add stages, including things like more and more IF stages and roofing filters and AGC stages etc you continiously add distortion to the signal. With the cleanliness of direct conversion you miss all that crud. Once the baseband gets digitized, there is NO more crud to be added, so you wind up with a high fidelity signal to play around with in the second conversion. The baseband could be any frequency, but it is down in the audio region because audio hardware (like the A/D converters) has a very strong dynamic range and very low distortion. People talk about direct conversion from RF to A/D, but the trade off is bandwidth vs performance. More band width = less performance.

Once you get the data into the computer, you can display it, and this is what you see on the panadapter:


a pictorial representation of the baseband audio that updates 30 times per second, virtually real time as far as your brain is concerned. This data is then acted on once more. It is demodulated. But you don't need a mixer to demodulate this data, what you need is an equation. The A/D shoots little slices of base band data into memory "bins" in the computer, and the computer sucks up the base band data and runs it through one type of equation and what comes out is a little filtered slices of the base band, and that is what gets decoded to audio. You choose what slices you want to listen to and pop then into an equation that demodulates the slices and filters the slices and then reintegrates the slices into analogue audio you can hear in your headphones. The width of the filter for you audio is entirely under your control, as are the skirts of the filter. This is how Flex obtains its "brick wall" filtering. If you click the above pic you can see what a 100hz filter looks like in the panadapter It is represented by the green line. If you want CW, you send the data through another equation and out the other end of the equation comes CW. If you want LSB you send the data through a DSB equation, and then set the upper sideband half of the data to zero. All that is left is LSB. The filters are completely adjustable if you want a 112hz filter you just dial it up. The filters do NOT ring even at 11hz. I used this to great advantage in one DX contest. Before I discuss the contest experience, I want to discuss this picture:


This is a pic from Gerald's excellent article in QEX, and it was this picture that captivated my imagination. What you see is a "bin" representation of a DSB signal. Each bin contains the data that gets sent through the FFT (fast Fourier transform) equation that returns it back to audio. If you want LSB you just set the value in all the bins on the USB side to zero. A perfect filter! The notion is so simple, so elegant, and so powerful. Back to the real world, and why all this software/math mumbo jumbo matters, back to the world of contesting!! (how real is that?)

I was on 160 in a contest, and there were 2 stations that were 40 hz apart (I measure the difference). The stations were in the S-2 range about -100dBm. One station was in the south Carribean and the other was in Eastern Europe. There were about a dozen S9+ US stations calling either one or the other of the DX stations. With my SDR-1000 I was able to narrow down the filters to minimum, and work each station as a single entity. I brought my Orion up on freq, with its roofing filters and all that, and I could not duplicate with that 3500 buck radio what I did with my little 1200 buck black box. The filters truly are brick wall, and the filtering happens in the computer. At no time did I experience any intermod or blocking or even AGC pumping with the SDR. Many strong US stations all around me and 2 puny weak DX stations hugging the noise seperated by only 40hz. The difference of 40hz is on the very low end of noticability when trying to seperate signals, much less seperate the cacouphony caused by those signals and all the US stations calling them. I mowed 'em down with the SDR and went in the ditch with the Orion.

Roofing filters: who the hell needs em? They are expensive and inferior. They add distortion and are never narrow enough to do the job, except in "laboratory test" such as the ARRL testing laboratories. In my opinion ham radio today is held hostage to this testing nonsense. These radios like the Orion and the K-3 were specifically designed to the test. If you choose a roofing filter, and then choose a test that places one signal inside the roofing filter and one signal ARTIFICIALLY outside of the roofing filter, guess what YOU WILL HAVE A HIGH DYNAMIC RANGE. Big friggin deal. You have a really strong radio in an ARTIFICIAL test. A test the radio was specifically designed to pass with flying colors, and then that result is pounded and pounded into the ham radio psyche by ARRL advertising, as if it means anything. What it does is tweak the ego. It gives the blowhard at the ham club meeting material so he can look like the smartest guy in the room. And that's why we are obsessed with roofing filters. Not because we need them but because the smartest guy in the room needs them to look smart. In the real world when it counts, you just go in the ditch as Ihave just shown. In a future article I'm going to report some data that looks at the behavior of the high buck wonder radios when they are challenged with 2 strong signals INSIDE the roofing filter. That's a test the roofing filter radio wasn't designed to pass, but the F5K was, brcause the signal processing is handled in software and not hardware. It ain't a pretty picture for the legacy radios.

Because of the nature of the receiver the radio is very quiet. It was much quieter than the Orion or the FT-1000D. I think this is largely due to the simplicity of design. Less stages = less garbage = more intelligibility. Also the AGC is perhaps the best AGC I've ever experienced. Better than the Orion's even though the Orion had a very adjustable AGC. The original AGC in the SDR-1000 wasn't all that great. The design problem was attacked by a collaborator, a software engineer who knew a thing or two about AGC's and totally redesigned. Once the design was complete it was added to the PowerSDR code for download. One day I had a crappy AGC, and the next day I had the best AGC in ham radio. AMAZING!! If I wanted a new AGC in my Orion or FT-1000D I was screwed. Those radios are legacy radios which means the AGC is in hardware not software. I trust the power of this example is not lost on your imagination. In fact the issue is so bad that it can result in 15 years of bad design. The FT-1000 series of radios have always been bothered by key clicks. If you look at at 40M at night you can actually pick out the Yaesu radios by looking at their wave forms. They are terrible. This design problem was well known but Yaesu year after year, model upgrade after model upgrade, kept pumping out radios with this problem. Eventually W8JI published a modification of the radio that addressed at least to some extent the problem. But to fix the problem you had to break open the radio and attack the circuitry. The fix wasn't complicated, but it still required soldering. In addition if you fixed the "problem" you screwed up the QSK. So you were left with a dilemma. Fix the click screw up the QSK or be a lousy ham with a clicky signal, but maintain QSK. If you had an SDR radio you could fix this problem over night, and you could export that fix to the entire fleet of SDR radios with a simple download. DUH!!!

Here is a picture of the F5K architecture for comparison


The F5K has an interesting addition. If you add the second receiver, it becomes a triplex radio. Most transceivers are half duplex. In the old days when I got into ham radio we had a transmitter and a receiver that operated all the time. With this radio you can have 2 receivers and one transmitter all on at the same time. This gives you the ability to work SO2R from one box. It works. Or you can for example monitor 6M for openings on the panadapter while at the same time DX-ing on 80M CW. One click and your can make a contact on 6 and be back to 80 with nary a beat missed. I bet it would drive W9KNI nuts.

So that's my little riff on SDR for today. The F5K is considerably more complex than my trusty old SDR-1000, and does many more things but in its heart its the same radio with higher performance components and a smarter more versitile design, such as a better pipe between the radio hardware and the DSP inside the computer (firewire)

If you want to check out Gerald's QEX articles go here

"A Software Defined Radio for the Masses P1 to P4"

It will either bore the snot out of you OR BLOW YOUR MIND as you look into the future of ham radio.

73