10m FT8 RX on the cheap

This has definitely been on before, but as we approach sunspot maximum (and beyond) a timely reminder is in order. 

This works remarkably well and can be made very inexpensively, yet will bring in stations across the world most days. It may be built "dead bug" or, if you are really keen, as a simple PCB. As I have said before, it would make a great club project on a PCB.  The circuit is simple, so a single sided PCB should be straightforward. It means the "big rig" is free yet 10m FT8 may be monitored.

See https://sites.google.com/view/g3xbm4/home/hf-mf-and-lf/homebrew/10ft8r-rx .

20FT8R or 15FT8R anyone?

Whilst playing with the 10FT8R something occurred to me. With FT8, oscillators only have to be stable over 15 seconds. Many free running HF oscillators are far more stable than this even long term.

So, I think the crystal can be replaced by a just a tuned circuit making this receiver work on any HF FT8 frequency. All that really matters is reasonable long term stability and good short-term stability. All that's required is to scale the RF tuned circuit (one tuned circuit) and set the oscillator to half the FT8 frequency needed. I have not tried this but cannot see why it should not work.

This may work as high as VHF where I have made free running oscillators work even on 2m.

Do not be afraid to experiment! 

This should make the whole receiver very low cost indeed. It would not surprise me if many can make the entire RX for less than the cost of one coffee out.

14.037MHz crystals for the 10FT8R

Jason M0NYW has just forwarded me some 14.037MHz crystals that came originally from Jay W5OLF. These are for use in my ultra simple 10FT8R receiver for 10m FT8. This should simplify the oscillator and allow me to remove a toroid inductor. I hope to try this shortly.

Facebook memory today

This photo shows a FB memory from 9 years ago. It later occurred to me that you the same idea would work on FT8 RX so the FT8R was born. See my main website at www.g3xbm.co.uk. 

10m FT8 with the 10FT8R and the tiny indoor loop

Since before breakfast I have been on 10m FT8 RX with the 10FT8R and the tiny indoor loop. 26 spots on RX so far (at 0803z). The loop is thin wire just 50cm across, indoors on the shack windowsill. The 10FT8R is a simple direct conversion receiver shown again below. 

As mentioned yesterday, I got the 14.040MHz crystal from 3rd Planet Solar in the USA. It was very inexpensive. The whole RX is incredibly inexpensive as you can see!  

My thanks again to Jay W5OLF for doing the schematic - much better than my hand-drawn effort!

UPDATE 0855z: At 0815z, I changed the thin wire on my tiny loop to 6mm diameter copper central heating pipe. It tunes more sharply so is probably a bit more efficient. At the moment, 52 stations spotted today on RX.

UPDATE 1018z:  Currently, 86 stations spotted on 10m FT8 RX (see map).

UPDATE 1237z:  113 stations spotted on RX so far today.