Morning Dale, Passband Tuning can be incorporated into a single conversion receiver which uses a product detector. The method used in most commercial receivers for amateur use (putting aside DSP) is to have two IF filters in cascade along with mixers. By varying the injection frequencies to these mixers the passband of one filter can be made to 'slide over' the passband of the second filter thus changing the overall IF bandwidth. The input and output signal frequencies are sometimes kept to be the same, sometimes not. It is desireable to do this early on in the receiver chain, but it has been achieved in an outboard addition using audio input.
If you view a single conversion receiver which uses a product detector as a dual conversion receiver with the second IF being at audio, then you will see the makings for Passband Tuning and IF Shift are there. The second IF filter required for Passband Tuning would be a good audio filter with steep skirts, although audio DSP might help here if its intermod performance is good. Please understand that I am risking some oversimplifications for the sake of Reflector bandwidth. The problem with implementing anything extra into the K2 which involves tight control over the LO (VCO) and BFO frequencies is, I understand, the firmware. This could be the deciding factor. 73, Geoff GM4ESD Dale WC7S wrote on Friday, February 09, 2007 at 12:21 AM: I would like to have a way to "adopt" a circuit for passband tuning, similar to what was in the Drake R4B or in the Icom 761. What would be involved to incorporate something in that area? Is it a non-item, from the view of single conversion? Thanks, Dale --... ...-- Dale - WC7S in Wy _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
