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


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!!!!