> > Another point -- some have noted that at least some of the > > roofing filters are actually wider than their nominal value. > > By design, INRAD makes the actual -6 dB bandwidth greater > than the filter name. See the actual analyzer plots on the > Elecraft web site.
This is a throwback to the practice by Kenwood and Yaesu in the first transceivers with cascaded (8 MHz/455 KHz) filters. The filters were specified based on the effective bandwidth of the cascaded pair. For example, the "Standard" Yaesu "2.4 KHz" filters were actually 2.6 KHz wide (note the original model numbers were XF-ffff-262-xx) - the cascaded pair resulted in an effective bandwidth of 2.4KHz. The same effect can be observed with Inrad's filters. Looking at the 250 Hz pair for the TS-940, the 8.83 MHz filter is 367 Hz wide at -6dB but it is down about 2dB +/- 125 Hz from the center. when this is combined with a 455 KHz filter that is 265 Hz wide at -6db and 250 Hz wide at -4 dB, the effective bandwidth is slightly less than 250 Hz. 73, ... Joe, W4TV _______________________________________________ Elecraft mailing list Post to: [email protected] 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
