10FT8R 10m Simple FT8 RX
The 10FT8R is a simple DSB receiver that I designed and made for 10m FT8. It uses only 4 transistors, yet works remarkably well. If you want a simple way to monitor 10m FT8, this may be your answer.
I used low cost 14.040MHz crystals pulled slightly LF with a Polyakov mixer that needs injection at half frequency in a direct conversion receiver. There is plenty of audio for the PC. I connected the audio to the mic input of the PCB without any special isolation. Crystal control is perfect for 10m FT8 as all activity is just above 28.074MHz. I found a low cost source of these crystals in the USA.
Mine was built with "MeSquares" (see www.QRPme.com) on a small piece of copper clad board. As a club project (ideal?), this might be better on a small PCB. I suggest this as a club project as this should be simple, useful and easily made. It should also be low cost. I am sure the whole RX can be made for the cost of a few coffees out.
As 10m gets better I am sure it will get stations from all over the world. Every summer there is sporadic E (Es) which gives good copy of stations up to about 1500km irrespective of sunspot numbers. Es signals can be very strong.
The 10FT8R can be made very small indeed. It also means the "big rig" is not tied up, so may be used for other things whilst 10m FT8 is being monitored.
The inductor in series with the crystal was to pull a 14.040MHz crystal 3kHz LF. I used a toroid in this case, but I suspect a molded choke should work.. It was 6uH in my case. If you can find a low cost source of 14.037MHz crystals you may not need this inductor at all.
The photo shows my breadboard: not pretty, but it works well.
UPDATE 17th May 21: I am experimenting to see if the last audio stage may be omitted. If so, this receiver would be even simpler.
UPDATE 23rd May 21: My sincere thanks to Jay W5OLF for doing a proper schematic. He is working on improvements and a PCB. The crystal was obtained at low cost from 3rd Planet Solar in the USA, who currently have good stocks at $1.50 each.
UPDATE 7th August 21: If you can get 14.037MHz crystals , the inductor in series with the crystal can probably be removed.
Typical reception on a May day with a tiny indoor loop antenna.