The Elecraft "250 Hz 8-pole" crystal filter is 370 Hz at the -6 dB point. You can run the DSP down as low as 300 Hz with this crystal filter and have minimal roll-off of the 170 Hz shift RTTY signal.
In practice, I have run 200 Hz DSP in large RTTY pileups with great success in contests for months now. Yes, there is roll-off, but the narrower filter eliminated more of the pileup so that the net result was faster clear copy of at least one call sign, compared to even a 300 Hz DSP bandwidth. This trade-off was a net advantage. In non-pileup situations, the 300 Hz DSP bandwidth with the "250 Hz" (actually 370 Hz) crystal filter is as narrow as you should, especially for weak signal reception. Furthermore the 400 and 500 Hz crystal filters are nearly as good as the 250 (really 370) for this application as roofing filters. In few cases, if any, will you be able to tell any difference between these three roofing filters. 73, Ed - W0YK > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:elecraft- > [EMAIL PROTECTED] On Behalf Of Axel Kaiser > Sent: Sunday, May 18, 2008 5:15 AM > To: Elecraft Reflector > Subject: [Elecraft] RTTY filter for K3 > > > > > > To all you filter aficionados, > > first of all thank you very much for all your detailed answers to my > original question, which roofing filter ist best for RTTY operation of the > K3. Lots of very detailed and informative answers were given and even a > general discussion on this issue among several others was started. But to > tell you the truth, I am still somewhat uncertain, which filter to order > with my K3. > One of my theory books about HF technology, modulation, bandwidth and so > forth, tells me, that the necessary bandwidth for a 170 Hz shift RTTY > signal should be around 320 Hz. Now some of you guys write, that you are > using a 250 Hz filter for RTTY operation. A 250 Hz filter though has this > 250 Hz (ok, a few Hz more in reality) bandwidth at - 6dB attenuation, > which means that the actual bandwidth at about 0 db is even less. > So my understanding for a 170 Hz shift RTTY operation is, to use a filter > of at least 400 - 500 Hz (at -6dB) in order to get all the information > through the filter. This I can confirm also with my current OMNI VI+ which > does not allow me to copy RTTY signals with a 250 Hz filter . So please, > where is the point which I am missing with the K3, that you can work weak > RTTY signals with a 250 Hz roofing filter?? > > Best 73 de > > Axel, DL3ZH > > > > _________________________________________________________________ > Discover the new Windows Vista > http://search.msn.com/results.aspx?q=windows+vista&mkt=en- > US&form=QBRE_______________________________________________ > 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
