[Collins] Inrad 2.5 KC Mech Filter Assembly

[Dr. Gerald N. Johnson]

On 1/19/2012 3:14 PM, Bob and Sue Jefferis wrote:
> I am wondering why you would need to change BFO frequencies in a
> receiver. The original BFO XTAL frequencies are placed symmetrically
> above and below the 455 kHz filter center frequency.
>
> A transmitter, like a 32S-3, would indeed require new BFO or 1st IF
> XTALS since they [Collins designers] relied on the mechanical filter
> to provide at least 20 dB of carrier suppression. Am I missing
> something?
>
Sideband suppression is handy on receive like its needed on transmit and
placing the carrier down the slope gets adequate opposite sideband
suppression, transmit or receive. The passband skirts have a finite
slope. Then if you want to transceive you need matched filters and
crystals in transmitter and receiver. If you are willing to not use the
transceive mode (where the transmitter frequency is set by the receiver
crystals and PTO) but manual spotting, using the front panel adjustable
BFO in the S-3B/C works fine for getting the opposite side band
rejection on receive.

> I use Inrad/Collins  500 Hz filters in my 75S-3B receivers for CW ops
> with excellent results. I agree, the time domain transient behavior
> (ringing) is improved in the modern torsional filters.
>
> Aside, from the possible side effect of increased 120 Hz or 60 Hz
> noise, I would suggest trying the 2.5 kHz filter before changing it.
> Again, am I missing something here?
>
> 73, Bob, KF6BC

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.