Quote:
Originally Posted by turretslug
Taking a "sniff" from a classical simple valve HFO like this takes a little care and thought- enquiries on the 'net will throw up innumerable gurus who will glibly say, "just stick a J-FET source-follower buffer on the LO grid". That's not good enough, maybe it would serve on emitter/source/cathode of a Colpitts/Hartley-type VFO but the stability of the type of oscillator here is very, very critical indeed on both stray capacitance and impedance characteristics of anything connected to it. At the top end of the highest HF band, i.e. around 30MHz with sets like this, even moving a finger around the oscillator components can produce a shift of tens of kHz!
Colin
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That's an interesting perspective on things and will be added to my file on adding DFC's to receivers! My on-going "multi-year" rebuild of my HRO eventually plans include the addition of a DFC, and as you say, the fet buffer is fairly ubiquitous, but may well be a sub-optimum solution!
B