This weekend I was intending to put the schematic of my 10m FT8 RX on this blog. Sadly, I had no time. The weather was dry so I was gardening.
Hopefully it will be up within the next few days. Please accept my apologies. If I had found my SPlan CD I could have done it. I have to master a new tool first!
Earlier posts show the 10FT8R 10m FT8 RX works as expected. It is spotting a similar number of stations to those spotted on my FT817ND with the tiny indoor loop. With a "proper" 10m antenna outside, I am sure many more would be copied. At a guess I would say my loop is at least 6dB worse than a dipole outside. It is also quite directional. As soon as my son can help, I shall get a wire dipole erected.
One issue I had was how do I net it without a frequency counter? This is the method I used. I set up the "big rig" on 10m FT8 with WSJT-X but set the frequency to 28.073MHz rather than 28.074MHz. I then adjusted the oscillator frequency until I spotted a faint signal at 1kHz audio. Voila!
Simple. Lots of stations spotted today.
A few moments ago UA2FBW (1365km) was spotted on the 10FT8R RX with the indoor loop. The RX is on all day. It certainly works! His signal was strong.
UPDATE 1205z: 18 stations spotted on RX so far. The 10FT8R is obviously working on the small indoor loop antenna!
I had a few problems getting the crystal pulled down enough, but a small inductor in series with the crystal did the trick. I shall tell you how I netted the crystal in another post.
So far, ES2AJ (1716km) has been spotted using just the indoor loop at -12dB S/N, which is strong. This means the "big rig" does not have to be tied up when monitoring 10m FT8.
In the end I started with my WISPY RX which I found. The sharp eyed may notice an unused oscillator buffer which can be removed from the board. A simple PCB could be made if this was ever a club project.
All being well, I shall publish the circuit over the weekend.
It is nearly finished, but I was unable to pull the 14.040MHz crystals low enough, so I shall have to modify the oscillator slightly when we get back, as we are going out this morning.
I can get within 700Hz with just capacitance in series, but I shall have to add a little inductance too. I was hoping to stick this RX on when out, but I shall have to wait. At least it oscillates!
This photo shows the original WISPY 10m WSPR RX, which I want to base the design on, although I am still looking for the actual thing. I am not sure I still have it even! At least the photo will help with pad placement.
As my fine motor skills are not as good as they were, I have decided to start with a receiver based on WISPY for 10m FT8 using 14.040MHz crystals pulled very slightly to 14.037MHz and a Polyakov mixer. Polyakov mixers need oscillators running at half the received frequency. This also means the radiated signal from the oscillator is very low.
At some point later, I will extend this to a full FT8 transceiver. The receiver will work with free WSJT-X software running on the PC.
As 10m gets better, the whole world should be spotted on a receiver that is unbelievably simple costing the same as a few drinks out. Of course during the Es season 10m is good out to about 1500km at any point in the sunspot cycle, so this RX may be used at other times too without tying up the "big rig".
