Chen, Very interesting. Thanks for your link.
Have you looked at the waveform with the AFSK TX Filter turned on? Rick K6LE On 6/12/2010, at 9:09 , Kok Chen wrote: > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
