This is the 6M RF preamp circuit, build using MPF102 N-Channel RF Amplifier. It really is pretty much like a 6M two-stage preamp that published in QST during the mid eighties. Doug truly favored the grounded gate FET for narrow band preamps. His published work is replete with good examples of them on just about every band. I assembled that amplifier and consider acquiring about 10 dB gain, that is all that I desired for the 6M direct conversion receiver working with a diode ring detector that I was developing. The fantastic feature of the amplifier is the fact that it integrates a band pass filter and preamp in one.
The shield displayed in the schematic diagram was a small piece of grounded, double sided PCB in which, I built a small chamfered hole in to pass the lead going to the T2 tap. The shield, together with fairly short component leads will assist to reduce parasitic oscillations. The T2 tap is 3 turns down from the end of the T2 primary winding that joins to the variable capacitor. Doug specified T37-10 cores for the inductors, but I replaced T37-6 cores and applied the same number of windings as specified for the T37-10 core inductors. It worked fine.
6M RF Preamp using MPF102, circuit source page: www.qrp.pops.net
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