20-08-2014, 12:46 PM
The varicap tuning should tune ok in use with your radio even if the FET doesn't work, that's assuming the FET doesn't have a G to Source or G to Drain short.
Check that the voltage on the varicaps cathode is varying between it's voltage parameters when the tuning pot is rotated, the tuned circuit should definitely peak up at the frequency your radio is tuned to.
The non working Q multiplier might be a wiring error or the FET, for it to work the feedback needs to be of the opposite phase to that of the tuned circuit, sometimes swopping the feedback winding connections can solve the problem if originally they happened to be connected in phase with the tuned coil.
Good luck.
Lawrence.
Check that the voltage on the varicaps cathode is varying between it's voltage parameters when the tuning pot is rotated, the tuned circuit should definitely peak up at the frequency your radio is tuned to.
The non working Q multiplier might be a wiring error or the FET, for it to work the feedback needs to be of the opposite phase to that of the tuned circuit, sometimes swopping the feedback winding connections can solve the problem if originally they happened to be connected in phase with the tuned coil.
Good luck.
Lawrence.
