It *is* difficult to build very narrow 8-pole filters with low loss. That's one reason Elecraft offers a 5-pole, 200-Hz unit.
5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD dynamic range using the 200-Hz filter is outstanding. We've had some requests to offer a 270 or 300-Hz 5-pole filter, which would be better optimized for narrow-shift RTTY than the 200-Hz filter. We're also considering a dual-passband filter (500/270 or 500/300) that would fit in one slot. 73, Wayne N6KR On Jul 15, 2010, at 10:18 AM, Jim Brown wrote: > On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK wrote: > >> Agreed. 250-270Hz would be the "sweet spot" for an 8-pole filter, to >> guarantee good sales for the manufacturer *and* good performance >> for a >> range of users in heavy QRM. > >> Now let's see if Inrad or Elecraft take the bait :-) > > Hang on a minute, guys. Inrad builds a nominal 250 Hz filter, Elecraft > tests and re-sells it, and we buy it, because we've agreed that it's a > sweet spot operationally. > > The issue is that it's wider than than at the -3dB points. So the > problem appears to be that it's pretty difficult to build an 8-pole > 250 > Hz filter at 8.8 MHz, and that Inrad has given up on doing better. > > 73, Jim K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
