It appears that those little receivers can easily be turned into transmitters. I got some ideas in my mind, which I will successively add to this post, so, stay tuned.
For a 10MHz I.F. and a crystal controlled LO, please see my earlier post. For QRSS I would favor 7000800Hz, 14000800Hz, 21000800Hz and 28000800Hz, since crystals (oscillators) are available for 3MHz, 4MHz, 11MHz and 18MHz.
More cheap crystal combinations could be found on my web-page. Note that only pairs with M=1 are "drop in" compatible with N3ZI's PCBs.
One nice option appears to be a dedicated 17m WSPR receiver, or maybe even a transceiver. This design would make use of a 8.000MHz I.F. and a 10.106MHz crystal (30m QRP). A tiny bit of pull and the carrier frequency should be 18.1046MHz.
600m is easily available with the following crystals: 5.000MHz - 4.5000MHz - 4.000MHz - 3.500MHz - 3.000MHz - 2.500MHz - 2.000MHz.
Remember, the subtractive mixing product compensates for thermal drift of the oscillators.
Transmit?? you may ask yourself... Yes, I believe that Douglas' PCBs are equally suitable for generating a single side band signal. Please have a look to the schematics on N3ZI's webpage.
A modification to a transmitter, in my view, could be the following:
- feeding an AF signal to pin 1 of U1, the input filter and transformer make place for an AF network
- X6 should have the same frequency as the filter-crystals
- U2 is now a converter, thus, X5 serves the LO
- Q2 a buffer, C17 should therefore be replaced by a some means for linearizing Q2
- C22's capacitance should definitely be reduced
Two PCBs will provide a nice and easy transceiver. One PCB just like intended, the other modified for transmit as shown above. Here, some additional considerations seem appropriate:
- feed the BFO from the RX board to U1 of the TX board, alternatively use an external BFO
- feed the LO from the RX board to U2 of the TX board, alternatively use an external LO or VFO
As soon as I got the first results, I will write an update on this site. Stay tuned....