On 11/8/22 1:31 PM, Donald S Brant Jr wrote:
On Tue, Nov 8, 2022 at 04:06 PM, Jim Lux wrote:
FET would work well beyond it's nominal switching speed.
Because the FET is not really switching things at the RF rate, the gate being DC biased; the channel is just being opened or closed by the gate and looks like a bias-dependent resistor (plus all of its parasitic elements) on the RF side.
Best regards, Don Brant
In fact, that may actually help.. If the gate circuit is slow, that's great. The bane of switches is when the RF signal causes the switch state to change (a classic problem with diode switches, which is why biasing is so important). So you'd look at whether RF voltage can (capacitively) couple to the gate and move it from the desired state.
Pick a FET, use a stack of 9V batteries as appropriate to turn it on and off, and see what happens to S11 and S21.
(I seem to recall people using FETs, or attempting to do so, for spark gap replacement on a Tesla Coil - the switching speed required is slow (~100 Hz) and it's carrying a 100-300 kHz RF current.)
For a Tesla coil, one wants to be able to turn the switch off at exactly the right time.
