Hello,
I have just uploaded a file with the results of my measurements of
the IF filters passband.
The set-up was a DDS-VFO as a signal source and a HF millivoltmeter
as a detector. I have measured the IF Filter including one amplifier
on each side. That are transistors Q11 and Q12 und Ashhar circuit
diagramm.
A previous measurement of just the filter terminated with 56Ohm
resistors on each side gave a far worse result (less bandwith, >3dB of
bumpiness in the passband), which I think comes from wrong termination of
the filter. I did not know, how to terminate it correctly, thus I used the
amplifiers of the circuit.
I am impressed with the shape I have obtained, but the passband seems
a little wide.
Building continues towards the audio end of the BITX. I will then
repeat measurements with feeding audio in the mic and measuring
response in the IF.
73 Heinz, OE5EEP
