I agree with Joe's summary. Note that the "250" Hz 8-pole filter is really about 370 Hz at the -6 dB point. Any of the current "500", "400" or "250" Hz crystal filters will be fine for RTTY. With any of them, the DSP can be narrowed to 300 Hz without rolling off the outside edges of the two tones.
Note that the Dual-Tone Filter for RTTY is cascaded with the crystal and normal DSP filters and if either of the latter two filters are 250 Hz (at -6 dB) the three-filter-cascade will have significant roll-off on the outside skirts. This has the undesired effect of moving the two filter peaks much closer together than the 170 Hz split. That said, I have been running the 370 Hz crystal filter (aka "250 Hz 8-pole") with 200 Hz DSP and the DTF for several months now in RTTY contests. While the resultant passband was indeed rolled off as described, this was overall a net benefit in heavy pileup conditions because it filtered out the pileup better, producing a clear callsign quicker, despite the rolled-off passband. In other than heavy pileup conditions, it is best to keep the DSP at 300 Hz or higher, especially for copy of weaker signals. In the future, there will probably be a 200-400 (or 200-500) Hz variable 5-pole crystal filter that will be ideal to track with the DSP for high performance RTTY reception, ranging from weak signal to heavy pileup conditions. 73, Ed - W0YK > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:elecraft- > [EMAIL PROTECTED] On Behalf Of Joe Subich, W4TV > Sent: Friday, May 16, 2008 12:28 AM > To: 'n4lq'; elecraft@mailman.qth.net > Subject: RE: [Elecraft] RTTY Filter for K3 > > > > I am watching RTTY right now and using the 200 Hz 5 pole > > filter. The 170 HZ shift fits perfectly within the passband. > > After making extensive tests and plotting the selectivity curves > of the 200 Hz filter in my K3, I'm convinced that it is too > narrow for reliable weak signal RTTY operation, particularly in > conjunction with the dual-tone filter. > > The measured -6dB bandwidth of the 200 Hz crystal filter was > 209 Hz and the composite bandwidth of the 200 Hz crystal filter, > 200 Hz DSP and dual tone fitter was less than 170 Hz. A standard > 170 Hz shift 45.45 baud RTTY signal needs at least 235 Hz > (170 + 3*22.7) and the dual tone filter represents a 220 Hz (two > 50 Hz filters with center frequencies separated by 170 Hz). > > After extended discussion with a well know RTTY op and K3 beta > tester, I believe the combination of a 300 Hz 5-pole crystal filter, > 300 Hz DSP and the dual tone filter will have a composite -6 dB > bandwidth of about 250 Hz - about optimum for narrow RTTY. The > currently available, "250," "400" or 500 Hz filters in combination > with a 300 Hz DPS bandwidth and dual tone filter are very close to > optimum. > > 73, > > ... Joe, W4TV > > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of n4lq > > Sent: Thursday, May 15, 2008 5:29 PM > > To: Axel Kaiser; Elecraft Reflector > > Subject: Re: [Elecraft] RTTY Filter for K3 > > > > > > Axel: > > I am watching RTTY right now and using the 200 Hz 5 pole > > filter. The 170 HZ > > shift fits perfectly within the passband. > > > > Steve Ellington > > [EMAIL PROTECTED] > > ----- Original Message ----- > > From: "Axel Kaiser" <[EMAIL PROTECTED]> > > To: "Elecraft Reflector" <elecraft@mailman.qth.net> > > Sent: Thursday, May 15, 2008 3:52 PM > > Subject: [Elecraft] RTTY Filter for K3 > > > > > > > > Hi K3-folks, > > > > What would be the best RTTY roofing filter for the K3? Is the > > 400Hz 8-pole > > filter too small and the 500Hz 5-pole filter the better choice? > > > > Thanks in advance for your answers. > > > > 73 de > > > > Axel, DL3ZH > > > > _________________________________________________________________ > > Connect to the next generation of MSN Messenger > > http://imagine-msn.com/messenger/launch80/default.aspx?locale= > > en-us&source=wlmailtagline____________________________________ > > ___________ > > 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 > > > > > > -------------------------------------------------------------- > > ------------------ > > > > > > > > No virus found in this incoming message. > > Checked by AVG. > > Version: 8.0.100 / Virus Database: 269.23.16/1434 - Release > > Date: 5/15/2008 > > 7:24 AM > > > > _______________________________________________ > > 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 > > Checked by AVG. > > Version: 8.0.100 / Virus Database: 269.23.16/1434 - Release > > Date: 5/15/2008 7:24 AM > > > > _______________________________________________ > 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
