On Jun 12, 2010, at 6/12 5:09 AM, Richard Ferch wrote: > Brett Howard wrote: >> I do see FSK as a method that is slightly less prone >> to TX distortions. > > I have done some testing with a second > receiver, and my K3's RTTY signal seems to be cleaner in AFSK than FSK > (lower odd-order sidebands).
That is indeed correct. AFSK can potentially produce cleaner signals than FSK, as long the transmit IMD is good. Take a look at the last two figures on this page: http://homepage.mac.com/chen/Technical/K3/Digital/digital.html cocoaModem applies a filter to reduce the keying sidebands. Except for having two tones, the result is similar to what Alex VE3NEA had described in his CW keying experiments article in QEX a couple of years ago. The difference between FSK and AFSK can be even greater than what I'd measured if the K3 transmitter were cleaner. Waveshaping the keying signal created albeit small, temporal overlap between the two RTTY tones, whereas an unwaveshaped FSK signal has no overlap and can be used even with class C amplifiers. You can indeed see the low level IMD spikes from the in the last screen capture. 73 Chen, W7AY ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
