The first time I saw the term "passband tuning" was on the Collins 75A4 receiver. It shifted the BFO in one direction and the main PTO in the other direction. The two were linked together with a mechanical strap. The idea was that the pitch of the received signal would not change nor would the actual selectivity bandwidth. It was useful in both CW and SSB. The background pitch changed, but not the tone of the signal being received.
Then the Drake receivers came along, and did the same thing with the variable L/C filters in the 50kHz IF. A different approach, but the effect was the same. The passband could be adjusted from one side of zero beat to the other. I thought that PBT a great feature. Then I got a Kenwood TS-930S which had "VBT" - "Variable Bandwidth Tuning". This feature allowed for the adjustment of the difference between two edges of two filters - like opening and closing a sliding door - the "gap" could be adjusted wider or narrower, thus changing the selectivity. The center frequency does not change. You get continuously-variable selectivity this way and can respond to any band condition easily. Now I am used to that feature and miss it on other rigs 73, John W2XS. _______________________________________________ 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
