[RTTY] K3

[Kok Chen]

On Jan 6, 2009, at 3:20 PM, Joe Subich, W4TV wrote:

>>
>> The AD9834 DDS that it uses is definitely capable of FSK and
>> PSK, but both the FSELECT and PSELECT lines of the chip are
>> grounded in the K3, so I have a sneaky suspicion that the rig
>> might be a Keyed AFSK rig.
>
> I suspect Lyle is generating both PSK31 and FSK in the DSP and
> not creating external audio.

However, I suspect that it is the PA that is contributing to the poor  
IMD (because the IMD becomes quite respectable when I turn off the 100  
watt PA).  If the PSK31 envelope goes through any nonlinearity, you  
get IMD, no matter how you had generated the initial modulation in the  
first place.

As I mentioned earlier, you can slew FSK tones in a phase continuous  
way (instead of applying envelope waveshaping to each mark and space  
tones) and create an FSK signal whose envelope is constant and yet has  
bounded keying sidebands.  That might solve the RTTY problem, but it  
still wouldn't solve the PSK31 problem.

73
Chen, W7AY