Hello Dick and all,
well I rewound the ouput transformer.
Again I have problems, and when checking the signal on
a spectrum analyzer I found that it is peaking on the second harmonic.
So it transmits the main signal on 272kHz.........
136kHz is also present at the ouput, but much much weaker.
It really makes me puzzling.
You're lucky to owe a spectrum analyzer! It would have saved me a lot of
time in some projects...
However, if you have an oscilloscope as well, check the waveform on FETs,
should be fairly close to a square wave. Heavy ringing can pull the output
waveform almost to zero after the initial peak, thus making the double
frequency (at least this happened to me). Check also for possible coupling
of the ouput stage with CMOS driver. What helped in my case was a solution
by G3YXM (thank you!) : a capacitor around 1nF in series with around 22 ohms
resistor, both connected in parallel to the primary winding of the
transformer (marked as Z on the schematic here
I am still trying to get some motivation for finishing the RX loop...
73! Marek SQ5BPM