EMRFD Message Archive 1161

Message Date From Subject
1161 2007-11-11 20:48:35 bdebbasch Double-Tuned Circuits loaded with a FET
I have played with DTC (EMRF 3.14) and used RFSim99 to verify the
frequency responses. Everything match. My question is related to the
practical implementation of DTC in receivers (VHF as an example). In
those receivers, I am seeing the output of the DTC going to the gate
of a FET. The gate also has a resistor (generally a few k) to ground
and CE is much higher than the calculated value.

My questioni s the following: how is this circuitry presenting a 50
ohms load to the DTC? Simulation shows that the performance of the
filter is dramatically impacted when the loading impedance diverges
from the expected value. I am basically looking for a pointer that
show me how is the filter working in these conditions.
1162 2007-11-12 18:38:47 Allison Parent Re: Double-Tuned Circuits loaded with a FET