Quote:
Originally Posted by regenfreak
... Interesting idea. I can give it a try. ... The TinySA may have not enough power level in its RF generation output.
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Wait a minute. It is variant one of three.
If you use it with a 1m long piece of high quality coax cable, it will show ultra-low loading, pretty good amplitude flatness and essentially constant, nearly zero phase shift, from ~10MHz(-3dB low corner) well into GHz range, provided C2 (1000pF) is a leadless (chip) type and the diode is a small signal low capacitance type (no Schottky).
With its ~1pF (C1) input it would detune a bit IF tanks, but completely the front end. With its insertion loss of ~60dB and your TinySA (noise floor -102dBm @ 30kHz RBW, max sin output -6dBm) the max. available span for selectivity check would be ~36dB for a cold tank, increased by a gain (if any) in the hot state.
Removing the C2, you get a "narrow band" (a sort of high pass amplitude response with a slope ~20dB/decade) variant 2, with IL~50dB @10MHz and ~30dB @100MHz, and varying phase shift (not suitable for VNA measurements, but still usable for narrow band scalar sweeps). The possible span will improve by ~10dB @10MHz to ~30dB @100MHz (for cold unit). Loading @100MHz will be noticeable.
Now, adding a 0.1pF/500V (C01) in series to C1 makes up the variant 3. The IL will jump to ~70dB @10MHz to ~50dB @100MHz, but the span for hot unit with some gain would be usable. And now you'll get virtually no loading @10-100MHz band, and max. detuning @100MHz less than -200kHz.
Would it be a
crack enough?