Quote:
Originally Posted by karesz*
Hello,
if you need amplified signal- build please a plus transistor stage_i.e. as suggested in Andrew`s video at 21:00, it has a gain of cca 10...
Regards, Karl |
If I'm looking at the same circuit in the video, that JFET+BJT buffer only has a gain of unity from input to output. It looks like a classic unity gain buffer to me. It will do a reasonable job of driving a hi Z counter (or a typical 1Mohm scope input) via a short run of coax but I don't think it has any voltage gain from input to output.
It uses feedback to minimise the input capacitance but as a side effect of this it will typically introduce a lot of negative resistance at the input across the HF band and also up into VHF. So it can be unstable with certain (inductive?) input terminations and become an oscillator. But it is a classic buffer circuit
The simpler JFET source follower from Nuts and Volts will have a high input impedance but I think (at high frequencies) it will struggle to drive a reasonable (30cm?) length of coax with a 1Megohm//20pF scope or counter at the other end. So I think the frequency response will be poor if the coax and counter are connected to it.