My SupeRX/TX 40 — now on 7030 kHz
Click on schematics for a better view
Details on the receiver: https://archive.org/details/73-magazine-1991-04
Details on the transmiiter: https://archive.org/details/73-magazine-1991-12/page/10/mode/2up
Article on MXM Industries of Smithville,Texas:
Click on images for a better view
Click on images for a better view
Thanks for the details, William. For $1, a ready to go rig, easy to pack for travel. It looks smaller than your straight key!
I’m a sucker for cute little minimal rigs like this one from 30 years ago! Notice the reviews saying there’s ‘no drift even after switch-on’, with a free running VFO at 7.5MHz and another free running 455kHz BFO I find that surprising. Maybe expectations were different back then. Also note the ceramic filter hanging off the first NE602, no impedance matching, not even a DC blocking C .. a super simple superhet, if it works, don’t knock it. Paul VK3HN.
Thanks Paul. Yea it does show some hand capacitance effects on receive (which is annoying) but the crystal controlled transmitter is rock solid. As for the filter, I’m thinking that the impedances of the two chips might have been right at 1500 ohms — from my Q-31 adventures (inspired by your AM rig) I think this might be the right impedance for this ceramic filter. So maybe no matching network was needed? I am not sure of the width of the filter in mine, but it sounds too tight for SSB and a bit too broad for CW. 73 Bill N2CQR
The schematic of The Simple TX TX is missing a diode mentioned in the December 1991 73 Magazine article. The parts layout does not have the diode either. The photo is too fuzzy to tell if the diode is present. The last page of the article has a section called “Output Filter” and mentions that D1 is a 36 volt zener diode that protects Q3 from damage in the event an antenna is not connected when the transmitter is keyed.
Scott: I wouldn’t worry about it. You can put that diode in there, or you can live dangerously without it! My first HB transmitter had that diode in it. See page 68 here: https://ham.v4.si/books/QRP%20Classics%20-%20The%20Best%20QRP%20Projects%20from%20QST%20and%20the%20ARRL%20Handbook.pdf As I recall, there were times that I used the diode, and there were times that I did not. 73 Bill HI7/N2CQR
Thanks Bill! This is the circuit I have decided to build as the transmitter to go with the TJ DC RX (HSR). I modeled it in KiCad to experiment with a different build style.