Tuesday, April 28, 2009


v88htl was on 40M this morning. Band noise was -120 dBm and he was running -118 to -116. Copy was Q5 on the F3000. No muss, no Fuss. There sure as heck ain't nothin wrong with this RX!!


Monday, April 27, 2009


I was asked to write a review on the 3K, so I started thinking about what I would need to include in my review. I'm a pretty simple guy. Give me a little rag chewing, and low band CW DX and a latte and I'm happy. I like to screw around with some home brew too. My latest is playing around with some stepper motors to see if I can build a big honkin remote antenna tuner. Mostly I just want to learn something about step motors and their control, plus I have all these old ATX power supplies from old computers laying around with nothing to do, so I figured I'd make them earn their keep.

I decided in order to do justice to the article I'd have to do some "Digital". Digital for me is like a root canal. I've dabbled in it, I even ran across some old friends on 20M that I had completely lost track of, but sitting around reading brag tapes just doesn't do it for me. Its too much like robot radio. I especially don't like PSK31. The dynamic range of that mode is so bad that if you run more than 30W you blow out everyone's receiver and mess up the throughput. It offends my high power bully nature. (I don't like QRP either, but I'll save the rant for another day) BUT I know there is a whole group out there who finds digital modes (and QRP) fascinating, so my hat's off to them and it's worth a few minutes of time to do some kind of rudimentary intro of digital. One good thing about digital is you can go make the latte or take a leak while the brag tape is running.

I haven't had anything digital hooked up since the Pegasus days around the time of 9-11. For that I used a Buckmaster interface and wires everywhere from the sound card. I can't remember which program I was using, but it took half a day of screwing around to get it running satisfactorily. I think the program was MIXW or something like that. I thought it was a really cool program. I think the other hot program of the day was Digipan or something, which I could never get to work.

I use the DXlab suite, and it has a fully featured digital program called Winwarbler, so I figured I would see how hard it was to set up. The answer is it is trivial. All the connections are done in software. It is merely a matter of configuration. There is no interface no wires and no sound card involved. It doesn't matter if I have windows dings or dongs or chimes turned off or on, because none of that is involved.

I use a program called VAC to route audio. VAC is essentially a virtual audio cable (hence the name VAC) I simply through the software route the output of a program to the input of another. To set up Winwarbler required 2 cables. One cable feeds PowerSDR's audio stream into Winwarbler and the other sends the transmit stream from Warbler to PowerSDR. It was easy as pie.

Next I had to set up PTT control. I use a virtual COM program to route serial ports on my computer called vCOM. It gives me a virtual pair of ports that are connected together and wired in a null modem fashion. I name my virtual ports ten numbers apart, so for this project I chose 8:18.

That's it!!!! I tuned to 40M PSK31 freq and started decoding. I next tried the transmitter and before you know it I had 1000W of PSK31 blasting out into the universe on the big vertical!!! (I know I just gave some digital joker a heart attack. It was actually 20W) So that's it. I turned on the general decoder in the program and was decoding PSK stations--- bingo. I went to 30M and tried to decode one of those commercial RTTY stations on that band but couldn't get it to work, and my stepper project was calling my name so I'll leave RTTY for another day. There are many digital users on the Flex reflector that use RTTY, PSK, Slow Scan and all of the fancy modes. My point is with the F3K and a couple outboard programs, I had PSK31 working in about 3 minutes and I know exactly 0.0% about digital stuff. That is how easy it is. PowerSDR has a dedicated digital mode with upper and lower sides. If you look at the top picture you can see the digital specific controls. It made it very easy to adjust the various gains in and out of Winwarbler. I think there has been some things done to adjust AFSK so you know what freq you are on in RTTY but I have followed that discussoin only peripherally. Here is some Knowledge base articles about digital modes from Flex's knowledge data base (note there are 3l pages of articles of varying relevance). It turns out there is an article on how to set up Winwarbler, so I'll have to read that sometime.

Here is another shot of the setup this time with all three screens visible and the F3K panadapter shifted to "PanaFall" mode. I expanded the bandwidth 4X on the scope for this view

As I was preparing this screed a fellow dropped me a note because he is considering a F3K and has an interest in digital, so I took the screen shots above and at the top of the page to give an idea of what it looks like. Unfortunately there were only a couple stations on 40 tonight. I hope this simple minded presentation helps him in his decision.


Of ZL's VK's and Summer Time Static

Here is a shot of the F3K console. It looks just like the F5K console, and that is because it is just like the F5K console. There are a few things missing, for example there is no "Antenna" sub screen since there is only one antenna port, and the RX2 aspect of the program is dormant, but otherwise it is pretty much exactly the same. Because it is the same, the performance between the 2 radios is virtually identical I have grown accustomed to the dual receive in the 5K, and the ability to control multipe antennas and signal paths. I have 3 seperate antenna/Amp combinations set up on the 5K as well as a couple seperate RX antenna scenarios, so I can DX while I am ragchewing on 75, or run SO2R. This is impossible on the F3K without making it happen with external complex switching schemes. That is the power of the F5K it allows you to multiply the functionality of the station right out of the box without going through that design nightmare.

I have all my rig connections coming out to a patch panel. On the panel I have 5 outputs from the F5K, one output from the F3K, one output from the SDR-1000 an output from the Paragon and an output from a six meter transverter. I also have I/O from 4 linear amps and 2 N8LP wattmeters, and an Ameritron tuner that show up on the panel. I have a seperate panel that allows me to chose which radio controls which amp. The F5K allows for automatic control of 3 amps, so when I want to use antenna path 3 for example I just click "ant 3" and the entire line from the radio to the amp to the antenna just comes on line. It is super convienient and super functional. If I am on ant 3 and I want to listen to a seperate RX antenna for RX2, I just click that in the ant screen and it become active. I don't have to unscrew antennas from the patch panel, or fiddle with antenna switches or any of that, just a click of the mouse and I go. This feature and the SO2R aspect is something I had some input on when the design of the 5Kwas being brainstormed, and Gerald has implemented it to a T.

The 3K is more simple. If I want to rag chew on 75, I connect my 75M Flat top to the patch panel, connect the F3K to the correct Amp, and rag chew. If I want to work DX I unscrew the flat top, screw in the verticals, change the patch panel amp control to the amp that is in line with the verticals and have at it. Much of the advantage of the F5K could be recovered using the macro function in DDUTIL and a bunch of relays, but not all. But if you leave out all this fancy station control and complex operating techniques like separate RX antenna and dual diversity reception, what is the radio's general performance?

I have been on vacation for the past week. We are at the end of my house remodel so I haven't been getting up to listen to the bands, I've been enjoying sleeping in a little before the hammering commences. Today was my first day back at work so before I headed out the door I took some time to listen to the south Pacific to hear what I could hear. ZL2AL VK6DU were coming through. The band was full of summer time static. The storms out in the Atlantic were doing their thing. Band noise was running -100 to -96. My usual band noise is on the order of -118 to -120. Above is a shot of ZL2AL just a tiny bit out of the noise, he was running -96, and the VK6 was about -98. With the F3K I was able to adjust the AGC-T and audio gain to make them Q5 no problem. I didn't even have to narrow the bandwidth below 100hz. I am not able to A/B the F5K and the F3K on the same computer because the driver won't support 2 instances of the radio simultaneously. Eventually this may come to pass, but probably NOT until the new version of the software is released. But given my hours and hours of experience listening to weak signals using the F5K I am confident there is virtually no difference in the ability to copy puny weak signals from half way around the world.

As I have said, I consider this radio system to be essentially a dual conversion radio, with the first conversion done in hardware and the second done is software (actually I consider everything before the A/D as the first conversion and everything after the A/D as the second, but the above description is close enough and easy to understand.) I never put anal perfection before clarity of thought. The second conversion aspect is identical in the 2 radios. The A/D itself is a stronger chip in the F5K, so things like dynamic range are stronger in the F5K, but in the 3K they have done an interesting thing. Included is a hot preamp and an attenuator of different strengths. What this allows you to do, by adding and subtracting gain is to center the dynamic range according to the band conditions. On a very quiet band you would turn on the preamp and thus plunge the dynamic range down into the noise to hear the weak one. On a band like 80M where noise abounds (especially this time of year) you would either run with no gain manipulation or you would add some attenuation to increase the dynamic range a little. Frankly I have never seen either this radio or my F5K overload, unless I specifically set out to overload it, but from an engineering standpoint I am glad Flex addressed this issue. The F5K has something like a 7dB stronger dynamic range compared to the 3K. The 3K is about as strong as the Orion.

So what's the upshot of all this? The upshot is the 3K is too cool. You get performance as good as an Orion, for like 1/3 of the money when you consider adding a couple roofing filters etc. You get a better bandscope and tuning scheme, and better filtering and a quieter receiver and greater control over how your radio sounds for 1/3 of the money. It is true you can run the Orion without a computer, but no one runs without a computer in the shack, and I saw a core 2 duo laptop with a 14" screen from Gateway advertized for $399 that will make this radio get up and do the boogaloo. (I remember the boogaloo: scary)

I had the radio running all weekend with the latest bleeding edge alpha code SVN version and it was rock stable all weekend. Not the first hint of a hickup. Flex has come a long way!!


Saturday, April 25, 2009

More 3K dope

Well I spent more time with the 3K today, and the radio is fantastic. I wrote a EHAM review if you are interested.

After putting this thing through its paces, I can't find really any difference between the 5K and the 3K in terms of its general performance. The receiver is hot. The TX audio is superb. I had a little flex radio pile up going on 40M for a while last night. What a hoot!! I'm a CW op and don't do much phone and certainly no pile ups so it was kind of exhilarating.

My general conclusion is for the money, or for a guy who wants the most bang for the buck radio, or you are on a budget, you can't do better than this. I'm impressed!


Friday, April 24, 2009


My F3K arrived Wed, and I finally had some time to install it today. I decided to intall it on the same computer that I have the F5K installed on. You can not at the present run both the F5K and the F3K simultaneously so I pulled the firewire of the F5K and plugged in the firewire of the 3K.

I had previously set up a new SVN version of PowerSDR in its own folder dedicated to the 3K. That is the nice thing about Flex radios, you can have several versions of the radio on the desktop all at once. I connected the antenna, a mic, a paddle, some headphones and a cable to run the amp, and hit the power button. The driver dialogue came up and 3 times asked me to intsall the driver (this is normal to get asked 3 times as different aspects of the driver load with each request). Once the driver configuration was completed I Powered up the version of PowerSDR I have devoted to the F3K.

It came up and I went through the initial configuration screens. There is a run once program that chooses the best fast Fourier transform for your particular set up called "Wisdom" (cute name), and that file is stored in the F3K folder to guide your computer n the fastest transforms and reverse transforms. Then PowerSDR starts and there is a couple of screens warning you this version is beta and dont goof around when running mobile. Mercifully both of these can be turned off once viewed one time. The config screen continues as some EPROM data is downloaded from the 3K and pretty soon you are ready to hit "finish" and the radio is ready to rock and roll. Total time from hook up of the antenna power etc to ready to transmit is less than 5 minutes. If you had to install the software it would be a little longer but certainly no big deal. Once this initial configuration business is done it takes 7 seconds to boot the radio on my system, which is pretty middle of the road by today's standards. (Core 2 duo O/C'd to 2.7ghz with 2 gig memory and 32 bit XP/SP3)

I attached all the software peripherals I like to run like skimmer and DXlab in the setup screens and that took and additional minute or so to go through all the set up screens of relevance. I have set up the radio a million times and I can buzz through each screen by memory. It is here where you set up the CAT I/O and VAC to run audio to skimmer etc as well as keyer inputs and things like that. I clicked on 40M CW and looked for some activity. This radio has the ATU built in, and I don't have that feature in my F5K so I did take a couple minutes to read how the ATU works in the supplied .pdf manual before I tried it.

I found an old boy in NC pounding out a CQ and gave him a blast and 599 was the first report on this little beauty. 100 Watts firing out my 66ft half wave 40M vertical. My contact needed to take a nap, (guess he was a little light on his beauty sleep, either that or my anesthetic personality put him to sleep) so I proceeded to fire up the amp and see how that works. I had my AL-80B in the line and in about 30 seconds had 1000 W on the wire no muss no fuss.

Overall this radio couldn't be easier to set up. To the newbie I'm sure there is a bit of a learning curve on how to operate the software, but as far as getting the hardware going, piece of cake.

So far the radio seems about the equivalent of the F5K in performance, but I have not done the weak signal stuff with it I normally do. It is a very quiet radio, and has a couple of features that my F5K does not have like the built in ATU and it has an attenuator in the front end as well as a preamp. These 2 devices in the line allow you to tune for best dynamic range for a given setup and band conditions. If I had stacked 4 over 4 40M beams on a 150ft tower I would probably need the attenuator. So far at least on 40M using my 1/2 wave vertical, just running the signal through the bandpass into the detector is best for me.

The CW experience was excellent. Virtually the same as My F5K. I tuned up the radio on SSB but haven't had a contact yet. With the radio I ordered a mic connector that turns the little RJ45 connector into an 8 pin Foster connector, as my mic uses that. PowerSDR allows you to make a recording of how you sound transmitting, so it is dead easy to set up your radio and make it sound EXACTLY how you want it to sound. In my case I like to run a little up-sloping EQ with a tiny, tiny bit of bass boost, and the CPDR at 2 or 3. I also like to set up the TX filter in the Setup screen to range from 150hz to 3100 hz cutoff. My my old bullfroggie voice sound beautiful. (You get sent to hell for lying :P). Once I had thing set exactly how I like them, I saved a copy of this transmit profile and called it Normal, so I can always return to Normal if I am screwing around with the controls.

My advice? If you have the slightest inclination in trying out SDR BY THIS THING! If you are an average ham who doesn't need all the bells and whistles of the F5K, like SO2R and multiple antenna inputs and out puts, BUY THIS THING! Personally I like screwing around with all the hoopla so the F5K is my kind of radio, but if I was living in a subdivision with a G5RV or some kind of multiband vertical and not much hope of putting up super duper outboard RX antennas and all that I would save the 1000 bux to spend on an AL-80B and live a very happy and enjoyable ham radio existence!

More as my impressions get fleshed out. We are a home schooling family and we use a writing seminar series on DVD to teach proper writing technique to my kids. I was watching the lesson for today and the guy said you should end the presentation with 1 2 or 3 bullets to nail home your point. 1 bullet was weak, 2 bullets was strong, and 3 bullets was super strong and 4 bullets was a Howitzer!

Bottom line: dead easy to get running, works good, works good, a ton of fun!!! BANG


Sunday, April 19, 2009

Rock n' Roll

I finished the softrock V9.0 today My version is complete with a band switched bandpass filter and covers 160M through 10M. I plugged in the firebox (presonus sound card) I am using as my A/D converter, the USB plug and 12V (it will run on anything above about 7.5V) and my vertical and fired it up. After I installed the USB driver, the radio came right online. I was using Rocky by VE3NEA as my software. This is the first time I've had a radio to use with R0cky so its a new experience, so I had to play with the configuration a little to get the right combination. One thing I forgot was to specify an output once I did that, I was on 40 CW!!!

This system is not like PowerSDR. It is much simpler in its character. The Softrock V9.0 is not exactly contiguous tuning using Rocky. The V9.0 has a Si570 programmable oscillator and the center freq of the oscillator changes in 20khz steps

Recall that its a broad band IQ signal that is fed into the A/D converter. I am running the A/D at 48khz so when I am set to 7020 on the programmable oscilator I can tune anywhere with in that 48khz window (from 6996 to 7044). If I want to go above 7044, I jut kick the Si570 up to the next programmed center freq. Here is how the radio sounds I have the bandwidth set to about 85hz in this recording.

Recall this is a $58 dollar kit. My intention is to set this up with PowerSDR and calibrate this radio and then use the S-Meter in PowerSDR as a field strength meter using a laptop on a wifi network configured as a remote base. I'm sure it will do that in spades.

The kit went right together and fire up the first time. It was fun to build. Make sure you follow the directions. I had to rewind a transformer because I presumed both input and output transformers were identical. They are not!! I caught my mistake before I installed the transformer so it was quick work to rewind it but it would have been better if I had been paying attention.

I will write more on this little beauty as I get more into its capabilities but for now, I recommend this little project. The quality of the RX is directly linked to the quality of the A/D converter (presonus firebox in this case)


Friday, April 17, 2009


The 3K shipped today


More to follow when I get my grubby's on it


Monday, April 13, 2009

This one will blow your mind

I was listening to SO4R tonight band noise was -103dBm (about S-4) with bad static. The SO4 was peaking about 6 db out of the noise. Some lid came on his freq with a carrier virtually zero beat, and as you can see the lid was a good 20dB louder than the SO4. (For comparison the SO4's relative strength was about like the station that is at 3505)

I started playing around with my controls trying to copy him. I decided to just wait till the bastard exited so I turned on the ANL to notch him out. When the ANL finished its notch I could hear the SO4 UNDER THE CARRIER. They were virtually zero beat only a few hz off at most but it was all I needed to hear the 20dB weaker DX station. What I heard was not a normal CW signal but it was like I was hearing a subtraction product of the carrier and the SO4, but I could clearly copy what I was hearing. I worked him a little later. I can't even imagine how that worked, but it sure did!!



Sunday, April 12, 2009

Flexwire I/O progress

The latest is out at DDUTIL regarding the progress on the Flexwire I/O Here are some shots of the prototype

The present design thrust is to add ALC to the F5K for use with a linear amplifier. An ADC has been added to sense and sample ALC voltage in a feedback loop. This is particularly useful with some of the transistor linear amps. Each socket has essentially 2 ports, One port follows for either VHF or HF bandswitching and one does not, DDUTIL has a macro function that will allow keyboard control of outputs that are not tied to bandswitching so for example if you want a switch that could put your linear in standby or a switch that actually powers up your linear that could be added to the mix quite easily. You say "why would I want to do that?" How does DXing by the pool sound, or maybe from across the country? In fact you could add a means to turn the F5K on and all you would have to do is start your remote desktop, start DDUTIL, power up your amp and F5K, then start PowerSDR and you would be ready to go. You could have DDUTIL do that macro all from one button press. DDUTIL can even turn your beam for you

Have a look


Thursday, April 9, 2009

3000 announcement

I'm going to cop out today and reprint Gerald's announcement on the 3K status. We are in the middle of house remodeling. The roof is done, I have new hardy board siding, we are mostly painted, and now the windows are about half in, so my mind isn't in SDR land this week. The trades aren't busy right now so it's a good time to get it done from both a price and getting the work done perspective. One of the guys who does landscaping around here has this on the side of his truck:

"We're different than all the rest..... We show up"

Cracks me up. I figure I've put about 1/4 of the populations around here to sleep so you get to know a lot of people over time. I did the epidural on my general contractors wife when she delivered their baby. It's spring and life is good

I'm very excited about the new 3K. I have one on order and I will be doing some review when mine shows up. I think I'm going to install it on a core 2 duo Lenovo Thinkpad with XP and a Samlex PS for testing. I may take it out to field day this year and see how it behaves in an environment of kludged up multiple transmitters. I may rig up a couple of 40M verticals down by the water's edge using some of these fiberglass poles and phase them.

Dear FLEX-3000 customers,

We are pleased to inform you that we are very close to first production
shipments of the new FLEX-3000. Circuit board assembly is nearing
completion and we expect final testing to begin early next week. If all
goes as expected, we plan to begin shipments by the end of next week.

The FLEX-3000™ is the newest member of FlexRadio Systems' high performance
fully Software Defined Radio (SDR) transceiver family. The FLEX-3000 is a
"direct descendant" of the FLEX-5000™, the full-featured, world-class
software defined radio transceiver for amateur use. Using the same FireWire
infrastructure as the FLEX-5000, the FLEX-3000 offers ham radio operators a
mid-range priced SDR that will continue to "just keep getting better" with
new performance and operating features. Moreover, new features can be had
trough free software updates downloaded over the Internet.

As with all FlexRadio Systems transceivers, the real power of the FLEX-3000
is unleashed when it is combined with FlexRadio's PowerSDR™ software. This
is the same software that is used by all FlexRadio Systems fully Software
Defined Radios.
In addition to the information listed above, there is also an extensive
Product Comparison Matrix on the web site that provides side-by-side feature
comparison of all FlexRadio Systems fully software defined radios.

Thanks to all of you who pre ordered the FLEX-3000 and have been waiting
patiently. We are confident you will agree that it was worth the wait.


Monday, April 6, 2009

AGC-T and hearing weak ones

This morning I was listening to VK9GMW out on Mellish Reef on 160. Initially I didn't hear him, but by and by I got things adjusted. The key was narrowing down the filters to 25hz and . I flipped on 50 and I could hear his signal. I flipped on 25 and raised up the AGC-T and I could copy him sending out reports he was weak to be sure but I could copy everything.

Over the weekend I have been busy with family and such. I happened to look at a EHAM article stating if your band noise on 80 or 160 is S-1 then you have problems with your antenna. This is such a ridiculous statement.

Here is my setup on VK9GWM. This shot was taken just after he stopped transmitting. This antenna is an inv-L, nothing fancy

Here is my band noise on 80 this morning

under S-1 My MDS is down around -138 with this set up which is why being able to adjust the AGC-T is so important. Even at -124 dBm I'm still 14 dB stronger than MDS, so its important to be able to adjust AGC-T. The AGC-T is the threshold is measured in - dBm and is were the AGC starts to reduce the gain of an incoming signal. My noise is 14dB stronger than MDS. Below is an example of a RX that starts its AGC at 13 db

This is the Racal RA6790/GM

and this is the RA6790's AGC curve run by Clifton laboratories on this RX

Near Textbook perfect is a circa 1970 receiver. Here are a set of curves from the K-2

Notice how the addition of pre-amplification changes the leftward part of the curves. You often hear that adjusting the RF gain is "just like" adjusting the AGC-T. Clearly these graphs tell a different story. In the cases where the RF amp is on it is the left end of the curve that is adjusted the most. The right end where the AGC is doing its thing is relatively constant. AGC-T allows you to adjust the knee of the curve. It allows you to adjust the point where AGC starts to happen to your radio. In the RA6790 example you can see that there is about 13 dB of head room between MDS and where the AGC starts to operate on the signal. Once the AGC starts to operate there is near perfect dB for dB reduction in gain for over 110 dB variation is signal strength. I don;t know the exact transfer curve of PowerSDR but in my experience it is probably similar to the RA6790, in terms of its linear aspect, but probably has a bit of an upward slope.

Note how important being able to adjust the AGC-T directly instead of by proxy. If you look at the way my RX is set up for VK9GWM, this is where AGC-T comes into play. As you recall my MDS is -138 dBm with the preamp off. My band noise is -119 to -120 dBm. If my AGC-T was set to 13dB like the Racal, my noise would be already forcing my AGC to work. With a signal only a couple dB out of the noise my ability to amplify that few dB is being squelched. To my AGC the VK9 is not much different than the noise, and just when I need the amplification my AGC is turning down the volume. With AGC-T, I can set the knee of the AGC high enough that the VK9 is still being amplified at full tilt, and often for weak signals this is the difference between copy and no copy. The audio sensation is often described as if the station "pops" out of the noise. My experience is that the station goes from non readable to readable.

It is a superior method to AGC adjustment compared to turning down the RF gain or adding attenuation to" tame" the AGC. The way it "sounds" is like the band becomes very quiet in terms of background hash. The fatigue of listening to a noisy band is much much reduced.

Here is a pic of the K-3 AGC

As you can see it is very complicated, with hardware parts and software parts. The various parts are

1 Weak signal
2 Below threshold
3 Software AGC active
4 Hardware AGC active

I've never used a K-3 but the Orion had a similar AGC-T setup and while it was better than my FT-1000D it was still never as good as the PowerSDR AGC loop. I've found this idea that hardware is somehow superior to software derived behavior to not be the case. In fact I have found this to be exactly opposite of the case.

I was in a discussion with a ham who was opining on "baseband" DSP and how they are all the same. It was clear he considered the DSP to be the tail of the dog. He made some kind of big distinction between SDR's that run RF strait into the A/D, and SDR's that convert to baseband. I found his understanding bizarre. And after looking at the AGC of the K-3 it becomes clearer. He still looks at the DSP as some kind of appendage to the "real" radio, instead of the other way around. I guess when you no longer have anything between your antenna and the A/D converter then somehow in his mind that is a different model. The distinction really lays in how much is between you antenna and your A/D. In other words if you have only a really tiny dog and a really huge tail, then perhaps it is the tail that becomes truly the thing of interest. Once the dog is taken to vanishingly small (as in the case of no hardware between ant and A/D), you are still left with the really big tail, and the tail becomes all there is, but it is in that tail where all the work gets done. In fact even if you have a very tiny dog virtually all the work gets done in the tail.

In a legacy radio like the K-3 there is a whole bunch of crap still between the antenna and the DSP The AGC curve tells the story. In the K-3, you see the hardware does subsume everything below it. In my own experience with DSP I can understand where this notion comes from. The DSP was basically an after thought added to the "radio" so it could be claimed as a "feature". In fact there were outboard DSP processors like the Timewave 599 processors that you could add onto any "radio". In the case of PowerSDR, there is only a single direct conversion between RF and A/D. Basically there is nothing that gets in the way of directly processing the signal. In fact PowerSDR could easily be rewritten to run one of these direct from antenna to A/D schemes. It would simply view the direct A/D as A/D data, and process it accordingly. In this kind of scheme PowerSDR is agnostic as to where it gets its data on which to operate. What gets into PowerSDR is something close to audio, but it is not audio. Because you hang the name "baseband" on it does not change its character. It is simply a down converted analogue of the RF. It is a signal 192kh wide. This is nothing like a Timewave 599 or some afterthought on something like the Omni-6. If you plug your headphones into this signal path you won't hear anything distinguishable, because the "radio" which resides in software has yet to operate on this signal and make it into something intelligible. In the case of something like the Timewave, the "radio" had already added all its distprtion etc before DSP. Its interesting how old judgments die hard.

I'm glad I've kissed the majority of the hardware goodbye.


Wednesday, April 1, 2009

In the middle

I have been discussing my antenna idea with my buddy K3RR. and he was describing his experience with a 4 square he had constructed where he brought all 4 feedlines into the shack and did all the phasing in the shack itself. This way he could change the phasing and retune the beam from the easy chair. He wondered to me about doing the same thing with my idea, just bring several feedlines into the shack and do the signal analysis from the easy chair. Visions of 8 foot tall reels of coax jumped into my head when ever I think about it.

He came up with an example, from K1LT's website Here is .pdf of K1LT's interesting version of the RX antenna I have been thinking about.

If you have a chance go read about this amazing design read about this. It uses 2x4 endfire elements for a total of 8 elements

Also take a look at his continued iterations on improving performance. It shows some of the practical reality of building such a complex antenna. Part of the reason I want the RX at the base of the antenna is to do away with all the vagaries of inversion transformers and miles of coax and the like and do what needs to be done in software. The thing that captured my imagination about SDR is the notion that to go to SSB from DSB all you have to do is set all the values of one side band to zero, IN SOFTWARE. With my old HT-37 phasing rig the side band was set to "zero" by a passive phase shift network in the radio. It worked to about 20 or 25 dB of supression and then the vagaries of discrete components (like tolerances) took over and the rest of the canceling was lost. I think the sooner you get to memory with the data the better

Also take a look at how he taught himself about digital radio

Very interesting