Anyway, in an effort to counteract all of this waterfall seduction and to show that us analog HDR guys can go panoramic too, I decided to try to create my own panoramic display without resort to SDR.
Of course, this is a very old technique. It was invented in the 1930s by Marcel Wallace, F3HM. He was the inventor of the Panadaptor which was the forerunner of today's waterfall. Panoramic reception was used by the armed forces during WWII. In 1946 Hallicrafters marketed a Panadaptor for its ham radio receivers (see below).
In figuring out how to do this, I thought back to my use of my Feeltech signal generator to scan the response of a crystal filter. The Feeltech has a very handy sweep feature.
In this case I set up the Feeltech to sweep from 4.85 MHz to 4.75 MHz in one second. With the 12 MHz IF of the BITX40 module, this would result in a sweep from 7.150 to 7.250 MHz.
The sweeping Feeltech just replaced the VFO on my BITX. I hooked up the Rigol oscilloscope to the audio output of the BITX. I set the horizontal scan rate at 100 ms per cm. This would have the trace go across the whole screen in 1.2 seconds.
After a bit of fiddling, I could see signals on the 40 meter phone band. But my display would kind of drift along the screen making it hard to know the frequency of the signals I was seeing.
Alan Wolke W2AEW provided the solution. He advised me to put a big stable signal at 7.150 MHz near the input of the BITX, then use this strong signal to trigger the 'scope scan. The HP8640B signal generator that Steve Silverman gave me (and that Dave W2DAB picked up for me in NYC) provided the triggering signal.
I put a piece of tape across the bottom of the scope display to calibrate the display. See video above.
It works! It is not as cool as the SDR waterfalls, and it does not convey nearly as much information, but it was a fun project.
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