Antonio Vernucci wrote:
I found a possible solution:

- with the receiver tuned at 14,139 kHz, the local oscillator works at 14,139+1,650=15,789 kHz
- should the local oscillator also have a component at half its frequency (i.e. 7,894.5 kHz), that component would convert an incoming 9,545 kHz signal to the 1,650 kHz IF
- this method also applies to the other two frequency cases

Any ideas on the reason and on the cure?

73

Tony I0JX / K0JX

I'd use an O'scope to look at the local osc. - see if the waveform is
"funky"... If it's not a nice sine-wave - that could be the source of
your "sub-harmonic"... which might cause the image you're picking up. Be
careful when probing with a scope - you'll want to use some sort of weak
/ high impedance coupling - certainly not a direct connection with a 1:1
probe, etc. If the local is producing some odd waveform - check the
power supplies / decoupling / tuning of the osc. Someone may have
cranked a slug or trimmer cap into some weird tuning that "sorta"
works... but not where it should be.

best regards...
--
randy guttery

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