I have a question. The standard IMD test is a two tone test. In a contest type situation with multiple strong signals in close proximity, wouldn't greater ultimate rejection by the crystal roofing filter be a significant advantage?
Mike W5FTD >>Do any field testers care of offer comments on the 2.7 k filter vs. >>the 2.8 > k? > Dick I'm not a beta tester but am familiar with > roofing filters because Orion had essentially the same > front-end as the K3 (main difference being its 1st IF was > at 9.0 MHz instead of 8.2 MHz). N4LCD recently asked a > similar question and I did not respond thinking someone > else would. They didn't so here goes for both of you. > The following are words by George W2VJN of Inrad > on page 6 of his excellent article on roofing filters: > http://www.qth.com/inrad/roofing-filters.pdf > *********************************************************** > 5. If 6 poles work so well, why not 8 poles? > The most important part of the filter > characteristic is from the pass-band on down > to about –30 dB on either side of center. Eight poles would provide much > better > stop-band isolation, but it’s not required in a > roofing filter and would make no > noticeable improvement in IMD performance. > *********************************************************** > Indeed his statement is borne out in the IMD numbers > Eric posted previously: > http://mailman.qth.net/pipermail/elecraft/2007-September/073442.html > Filter 20kHz 10kHz 5kHz 2kHz > 2.7 kHz, 5 pole 100+ 98 92 n/a > 2.8 kHz, 8 pole 100+ 100 93 n/a > The major role of a roofing filter is to prevent adjacent > (i.e. _______________________________________________ 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
