Dear Steve,
I myself have not bothered too much about the stability of my crystal mixer vfo because I am using it for normal CW only. But DJ2EY recently reported to me that he had also built my built crystal mixer. He has inserted both crystals into a massive copper block to achieve a good thermo contact between both (he is good in mechanical designs, his former profession), and he is really pleased with the stability (like DF3LP himself has been, who has also worked QRSS). But DJ2EY has used higher frequency crystals, he does not need any inductance in the vxo to cover the band, just a variable capacitor.
I hope this may help You in your decision.
73 Ha-Jo, DJ1ZB
"Steve McDonald" <[email protected]> schrieb:
Perhaps someone who has already 'been there' can offer their advice.
I would like to start building the exciter stages for what will be my 136KHz tx (hopefully we will have access to the band within the year!). The DJ1ZB exciter (modified by DF3LP) is the circuit that I am questioning. It mixes two xtal controlled 4MHz oscillators, 136 KHz apart, to extract the 136KHz signal. Can I build two VFO's, somehwere around 1MHz and set them 136KHz apart, that will be stable enough to handle QRSS work? I am worried about drift but also thinking that they may be stable enough if kept in the 1 - 2MHz region. As well, they should (if identical) drift by the same amount and thus be self-correcting? Is this a reasonable avenue to pursue or should I just break down and buy a couple of xtals??
Steve / VE7SL Mayne Island, BC
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