Quoted discussion from K2AV and W4TV: > > > > Anyone who asks us what filters to buy for CW contesting, we > > tell them 400/250 8 pole set to 450/350. Tried and true, not > > theory. > > > > W4TV and I will just have to agree to disagree. > > I don't think there is any disagreement ... unless you have > actually tried a 400/200 pair set to 450/250 and are trying > to say that the 250 Hz filter is tighter and suffers fewer > hardware AGC effects than the 200 Hz filter. If you try to > make that point, there are several others including W4ZV, > who will disagree with you. > > 73, > > ... Joe, W4TV >
The data I measured for the -30 dB down BW's of my 200 and 250 Hz filters supports what Joe says: 430 Hz for the 200 Hz 5-pole versus 500 Hz for the 250 Hz 8-pole. As a nearly 100% CW operator, I do like having three CW roofing filters in my rig. Matching DSP cutoff points to the various filters is another variable to play with, and thanks to Guy for the suggestions there. I do think there is a bit of a "truth in labeling" issue with regard to narrow crystal filters that needs to be addressed by the manufacturers. Not everybody will remember, for instance, that a 250 Hz filter may really have a bandwidth of 375 Hz. I recall a similar issue with a "125 Hz" filter that I purchased for my TS-850S some years back. The filter curve supplied by the manufacturer showed it was actually considerably wider than that (more than 200 Hz, as I recall). I can understand the difficulty in manufacturing very high Q multiple pole crystal filters, and that there might have been a design goal in mind that wasn't met. However, once we know that the design goal wasn't met, shouldn't we revise our labelling to more accurately reflect real world results? 73, Chuck Guenther NI0C K2/10 s/n 5853 K3/100 s/n 1061 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
