Agreed on the first point.
Yep I tried various resistances to ground on the whip, 10meg, 1 meg and a 470k trimmer, 50k seems to give the best performance, but its still unlistenable.
198 khz is radio 4 here in the Uk, it is a standard frequency its locked to an atomic clock, but this time I just want to listen to the broadcast, an hours riding early hours gets boring.
I couldnt find a proper schem for thsi car radio, however 'cept for the front end it looks like a standard 2 IF am receiver, the front end is tuned by a variable inductor, and the ant goes to a variable transformer coupled to the local osc tuning coil, then to a Rf pre amp.
The Ta7642 rx hisses, hums & some weird 50hz mains modulated crackle, tried it in 3 locations, very similar, the caps in the car radio are all dried out, however its reception is better, the noise is there but much less.