[RTTY] Crystal filter width preferences for RTTY contesting

[Kok Chen]

On Aug 27, 2009, at 8/27    5:44 AM, Dino Papas wrote:

> Interesting thread....I wonder if any "modern" rig actually does true
> FSK when you switch to that position?

Sure they do.  I can confirm that even though the FT-1000MP is not new  
anymore, it uses true-FSK.  So did the even slightly more ancient Omni  
V and VI.

The older Yaesus such as the FT-990 and FT-1000D used keyed-AFSK when  
you toggle the FSK keying pin.

The FT-1000MP does FSK through its direct digital synthesizer chip.   
The Omnis had a trimmer capacitor that was switched across a local  
oscillator -- which can go off tune over time or if the rig gets  
shaken during transportation (happened to my old Omni V when UPS  
shipped it from California to Yukon -- long truck ride from Vancouver  
to Whitehorse).  The Omnis are the cause of many of the non-170/200 Hz  
shift that you hear :-).

More modern rigs that are DSP based often generate FSK internally from  
I and Q signals, so you can consider them to a hybrid true-FSK.   
Mathematically, they are somewhere between keyed-AFSK and true FSK.   
Many software modems do all math internally with I and Q too, and the  
only difference between the AFSK they generate and the FSK of DSP rigs  
is whether the math takes place in the rig or takes place in the  
computer, the bandwidth of the in-phase and quadrature basebands, and  
one extra stage of "hardware" modulation where you need to be careful  
about maintaining linearity.

73
Chen, W7AY