[GreenKeys] Might be a bad weekend...

[Bob Camp]

Hi

One way to look at an FSK signal is as two ASK (amplitude keyed)  
signals. Since we don't run phase coherent switching that's usually  
what we have anyway.

With 170 shift and 100 baud your first "sideband" on the signal is 50  
Hz from carrier, the third is at 150 Hz. Since it's a square wave the  
odd harmonics are going to be there. 150 Hz is dumping energy very  
close to the "carrier" of the second signal 170 Hz away.

With 425 shift you get away from the problem. You can also tolerate  
more drift on the link. My guess is that drift / frequency tolerance  
is the bigger issue for the military.

Bob



On Dec 1, 2007, at 11:46 AM, Daryl Cline wrote:

> Is there a reason for the 425 shift vs the 170 ? The past 10 years  
> or so I
> have used the computer for RTTY and everyone seems to be using the 170
> shift. I am going to start designing my TU for my model 19. Guess in
> addition to invert I should design in all the shifts ???
>
> J. Daryl Cline WB4YEX  <><
> Harrisonburg, Va.
> -----Original Message-----
> From: wa3frp at aol.com <wa3frp at aol.com>
> To: kiddi181uk at yahoo.co.uk <kiddi181uk at yahoo.co.uk>
> Cc: greenkeys at mailman.qth.net <greenkeys at mailman.qth.net>
> Date: Saturday, December 01, 2007 11:31 AM
> Subject: [GreenKeys] Might be a bad weekend...
>
>
>> Hi!
>>
>> Best of luck with the testing weekend but the TARA RTTY Contest is
>> on-the-air on 20M and 80M, 40M, 15M, etc. this weekend.  It may be a
>> bad time to try the testing.  I'm usually available and can receive  
>> 425
>> Hz shift but will only transmit at 170 Hz shift.
>>
>> Running a Teletype Model 28 ASR and a few other pieces of gear that  
>> are
>> 40+ years old.
>>
>> GL + 73
>> Russ WA3FRP
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