Using SDR without SDR Hardware -- N2CQR Adjusts Analog BITX20 using Web SDR

I know what you are thinking:  Software Defined radio with the TOTAL elimination of hardware? WHERE IS BILL AND WHAT HAVE THEY DONE WITH HIM?  

Relax my friends.  All is well at SolderSmoke's East Coast HQ.  In fact, just yesterday I was making use of one of the systems described in this video.  Here's how: 

I was on 20 meters with my BITX 20 Hardware Defined (HDR) homebrew transceiver. Everything was going smoothly.  We have some sunspots now, so DX is once again possible.  I heard a loud U.S. station (that will remain anonymous) calling CQ, so I gave him a call.  

The trouble started right after he looked at my QRZ page. You see,  I have pictures of my homebrew rigs there.  These images sometimes trigger hostile reactions, especially from guys who have almost their entire stations INSIDE their computer boxes.  I also admit to occasionally making things worse by pointing out that it is possible to build a BITX20 for about five dollars U.S.   Some guys apparently don't like hearing about this. 

Anyway, the fellow I was talking to proceeded to give me a very blunt and harsh signal report:  "Well, I suppose your signal is strong enough, but your audio is TERRIBLE!"  Interpersonal relations pointer:  This is NOT a good way to alert a fellow ham to possible technical problems in the rig that he has built by hand, from scratch, in his home workshop.  Especially when the person delivering the harsh signal report is using a "rig" that was built by credit card in a robotic factory on the other side of the planet. 

So that QSO ended rather quickly. But I did want to follow-up in the comment about the audio.  And here is where I turned to Web SDR.   Mehmet NA5B has a really nice WEB SDR receive system in Washington DC, just about 8 miles east of me.  Before 20 meters opened, I called up Mehmet's SDR on my computer, tuned it to the frequency of my transceiver and watched the screen as I asked if the frequency was in use.  I then issued a couple of hopeless CQs, again watching the screen.    I could see in NA5B's waterfall that my signal was indeed seriously lacking in low frequency audio. 

Now it was time to turn to hardware.  Rig on the bench, 'scope and sig generators fired up,   I quickly determined that the problem most likely resulted from my placement of the  carrier oscillator frequency in relation to the homebrew USB crystal filter.  I had placed it about 300 Hz too low.  This resulted in a low AF frequency roll off not at the desired 300 HZ, but instead at around 600 Hz.  That would make the audio sound "tinny." So I moved the carrier oscillator up 300 Hz and went back to Mehmet's SDR receiver.  I could see that the lows were now at the right level.  Thanks Mehmet. 

One note about the audio coming out of the many SDR radios on the air:  When you look at the passbands in the Web SDR receivers you can see audio going almost all the way down to the frequency of the suppressed carrier.  With non-SDR rigs  you usually see a gap of around  300 Hz between the carrier freq and the start of the SSB signal.  This is often the result of our filter rigs having IF filter skirts -- you would place the carrier oscillator frequency a bit down the skirt -- this would help with opposite sideband suppression and all you would be losing would be the lows below 300 cycles, which weren't really necessary anyway.  I had placed the carrier oscillator too far down on the skirt.  

Of course, sometimes SDR rigs will also have a gap between the carrier freq an the start of the audio if the operator has set the passband this way, or if the microphone attenuates below 300 Hz.  But you see a lot of signals with audio filling almost the entire passband --some of the "Enhanced SSB" guys are running audio passbands that go as low as 50 Hz.  

Has anyone else noticed this "full passband" effect when looking at the waterfalls?  
Any other tips for using Web SDR for troubleshooting?