Hi
The Minimod is performing well, I have no criticisms of the design it is doing what it was designed to do. Connected up to my central heating pipe there is a very strong signal all over the house and it fades out about 30 yards up the road. I measured the power dissipated in R8 and it was about 2.5mW (1v 390r) when using a 5 foot aerial wire, it is possibly more when connected to the central heating.
I would imagine that if I had not studied the frequency output and tried to align it with a MW channel then I would never have suspected anything wrong. The listening radio would just need to be slightly retuned periodically.
The coil used as L1 seems to be reasonably stable after about an hour following adjustment, it makes no difference if the TX is powered on or off.
The current RF stability is about +1kHz when first turned on & -1.5kHz after a couple of hours so it is still more or less on channel.
Here is a trace on the scope of the output from the Minimod. RF frequency was about 1186.5kHz and the modulation frequency about 400Hz. There was no aerial connected, only the scope wires.
Things I notice are the lower lobes seem larger then the upper lobes, and what are those 2 additional wavy lines in the lower half.
Mike