Seems like anything from the 1.8 kHz on up to the supplied 2.7 should work fine.
Greg AB7R -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Bill W5WVO Sent: Monday, January 28, 2008 4:43 PM To: [EMAIL PROTECTED]; Larry Molitor Cc: elecraft@mailman.qth.net Subject: Re: [Elecraft] K3 filter performance All this leaves me wondering: What will be the best filter configuration (both TX and RX) for running FSK441 on meteor scatter? In case you're unfamiliar: "FSK441 uses four-tone frequency shift keying at 441 baud. The frequencies of the audio tones are 882, 1323, 1764, and 2205 Hz. Each encoded character uses three tone intervals and therefore requires 3/441 seconds (approximately 2.3 ms) for transmission. FSK441 accommodates an alphabet of 43 characters." -- from the WSJT manual by Joe Taylor, K1JT Bill W5WVO Don Wilhelm wrote: > Larry, > > You are quite correct that all filters are not created equal. For > digital modes, the group delay is just as important (if not more > important) than a flat passband and steep filter skirts. In fact, > those filters with steep skirts often sacrifice group delay to > achieve the steep skirts - but I am generalizing here, and that may > not be a universal truth. > > Unfortunately, group delay plots are not common for filters since > steep skirts seem to be the 'criteria of choice' for most amateurs. A > Gaussian to 6 dB filter has a nice rounded nose and gentle skirts, but > has a great group delay characteristic, OTOH, Cohn filters usually > have great skirts and poor group delay in the passband. Group delay > will make a difference in the ability to decode digital signals. > > 73, > Don W3FPR > > Larry Molitor wrote: >> --- "Joe Subich, W4TV" <[EMAIL PROTECTED]> wrote: >> For a died in the >> >>> wool >>> RTTY DXer, a steep sided 270 - 300 Hz filter would >>> be nice >>> instead of 370 Hz from the "250 Hz" filter. >>> >> >> Over the years I've spent a lot of time looking at >> this issue. My interest is primarily digging weak RTTY >> DX out of the noise but I do occasionally get into a >> contest. >> >> I've played with a lot of radios and filters but most >> of my real testing was done with a FT-980, a TS-2000, >> and a FT-2000. >> >> While I have seen good weak signal performance with a >> 250 Hz filter, it was the exception not the rule. As >> an example, the improvement on the FT-980 going from >> the stock SSB filter to the dual CW filter was >> dramatic. But going to the 250 Hz CW filter lost about >> 6 dB in ability to properly decode weak RTTY signals. >> It was even worse on signals that had polar flutter. I >> no longer have the plots of these FT-980 filters but >> as I recall, the 250 Hz filter was a bit peaky in the >> middle and had poor group delay characteristics >> extending well in from the corners. >> >> As you say Joe, the determining factor is the passband >> ripple/group delay. In a typical bandpass filter the >> group delay goes to heck at the corners. But the shape >> of the "corners" varies from filter to filter. I've >> run a number of "ham filters" on a network analyzer >> and plotted group delay. Seems like no two filters are >> the same even if the same part number. This I believe >> is due to ham filters being so cheap and manufacturing >> process control being minimal to keep the sell price >> down to what we can afford. >> >> So I would say, if you have a 250 Hz filter, no matter >> where it's placed in any radio, give it a try on very >> weak signals. Switch between a wider filter and the >> narrow filter and see if there is any degradation. If >> not, use the narrow filter. >> >> Other wise, plan on not using any filter less than 300 >> Hz in passband width (note - this is NOT the 6 dB down >> width!!! very important!!) if you want optimum weak >> signal performance. >> >> > _______________________________________________ > 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 _______________________________________________ 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 _______________________________________________ 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
