Bill, It is a matter of practical consideration. Most K2 BFO ranges will support a LSB filter width of 400 Hz centered at 1000 Hz. but not much more, although some have to be padded a bit to obtain that sufficient range. The USB filter is typically no problem, but RTTY is usually LSB. Narrow filters are usually more important for RTTY than they are for other data modes.
Yes, you are correct, images could be a problem if the transmit audio is overdriving the KSB2, but then I look at that problem as an operator consideration, and can be corrected easily - the K2 operates in a linear mode if it is not overdriven. MMTTY conveniently provides for a mark frequency of 910 Hz. That is the one to use with the K2. 73, Don W3FPR On 3/2/2011 8:06 AM, Bill Coleman wrote: > On Mar 1, 2011, at 9:30 PM, Don Wilhelm wrote: > >> My recommended RTTY filter set settings are - FL1 = The same as the SSB FL1 >> settings - that gives you the full waterfall display - FL2 = 1.00, FL3 = >> 0.70, and FL4 = 0.40. Those narrow filters are centered at 1000 Hz (change >> the KDSP2 RTTY filter centers to match), and set the MMTTY mark frequency to >> 910 Hz. When tuning PSK31 signals in the midst of QRM, use the VFO knob to >> tune the desired signal to the vicinity of 1000 Hz on the waterfall, and >> then if you need to narrow the IF filters to alleviate QRM, it is a simple >> matter of tapping the XFIL button. > Don, > > As much as I hate to contradict your expertise -- are you sure it is wise to > use such a low center frequency for AFSK RTTY? (Although it does more easily > fit the limited BFO range of the standard K2) > > Part of the reason RTTY tones are traditionally so high (2125/2295) is to put > any harmonics or other distortion products outside the audio passband. With > tones centered around 1000 Hz, the second harmonic, and much of the energy of > the third harmonic is well within the standard SSB passband. > > Also, if tones are centered around 1000 Hz, then the mark frequency would be > 915 Hz (1000 - 170/2), and the space frequency 1085 Hz. > > I chose 1500 Hz as a center frequency since it put the harmonics outside the > audio passband. (I use a rather narrow SSB filter - about 2 kHz wide) A > center frequency on 100 Hz boundaries allows KDSP2 filters to be properly > centered. I did have to make a minor modification to give the BFO enough > range to allow the crystal filter to be set at this point. > > Bill Coleman, AA4LR, PP-ASEL Mail: [email protected] > Web: http://boringhamradiopart.blogspot.com > ______________________________________________________________ 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
