Quote:
Originally Posted by regenfreak
Quote:
Originally Posted by nemo_07
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?
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I don't quite follow the logic of your three ideas. Why do you need such large IL as big as -70-50db for the LC tank to qualify to be "lightly loaded"? My NWT200 has only the dynamic range of 70db. The TinySA has the dynamic range probably of about 100db (it states 120db for its detector). |
You get it wrong way.
If you put a probe at hot end of 100MHz tank you get excessive detuning, unless the tip capacitance is ~0.1pF or less. The high IL is the consequence, not prerequisite.
You wanted Hi-Z probe with Lo-Z output, but found nowhere. So, here you've got a proposition. Take it or leave it.
Anyway, you are free to experiment with values of your choice.
Quote:
Originally Posted by regenfreak
I have 0.1pF smd capacitors but if you put two wires a few mm apart, its stray capacitance would be much bigger!
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It would be higher, it could be smaller. Look at the basics.
Or am I to believe that fabricating 0.1pF SMD capacitors is a pure nonsense?
BTW. It (C01) doesn't have to be SMD type. If you find and get a leaded 0.1pF one, the apparent paradox of wires will ... disappear. Right?