Michael AG5VG built a Sub-Harmonic Direct Conversion receiver. But then he took it a step further and moved it up from the 80/40 meter version that I had built, and used the same concept to run it on 20 meters using an oscillator on 40 meters (after some re-winding of the front-end coils). Using a station from Puerto Rico transmitting on 20 meters as an example, he starts out showing how well the receiver works in sub-harmonic mode (with the oscillator on 40), then quickly switches to normal Direct Conversion mode with the oscillator also on 20 (but using only one diode as the detector) -- he can still hear the Puerto Rican station in that mode. Very cool.
Good Evening Bill,
I built the Polykov and I attached a picture of it. I also used Pete's pre audio driver circuit from his jessystems.com site. Then I used an lm386 as the main audio driver. I could hear ft8 on the 40m band. Then I hooked the output of my lm386 circuit to a conventional set of computer speakers to really hear it. I am currently using an indoor wire antenna along the ground so it's certainly not optimal. Very fun build and I'll be learning more about it. When I have a better antenna system I'll hook it all up and send a video of it.
73s
MIchael
AG5VG
Bill,
I am just using a standard signal generator at 1 vpp output. The volume gets louder with every 100 millivolt I go up, but so does the noise. 0.8vpp was a little low for me so I bumped it up a bit.
The indoor antenna actually did surprising well but I'm looking forward to putting a wire up into a tree I have here. I just recently moved so I have to setup my outside antenna. I live in the San Antonio, TX area.
I am currently using three stages of audio amplification to be able to really hear it. 1st stage is Pete's pre audio driver, then an lm386, then a standard set of computer speakers.
I did plenty of playing around with it last night and the doubling function is so cool how it works. When I was around 3.538 MHz, with the variable cap tuned for the 7Mhz area, I was actually listening to 7.76Mhz, the FT8 frequency for 40 meters. I agree with You and Pete in a podcast you did a bit ago, that FT8 is great for seeing if the band is open and checking receivers with!
The next project is the art of the 3.5 - 4Mhz analog VFO and use it with the Polykov. I am very dependent on the Arduino/Si5351 pair as the code is available and easy to hook up.
Will keep you both updated.
73s
Michael
AG5VG
Two more videos from Michael:
Testing
Operation
I think this is a great example of good experimenting. Michael took the concept, made some mods, and put the device on another band. FB.
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