Re: [RTTY] Fun, but

[Kok Chen <chen@mac.com>]

On Mar 2, 2009, at 12:24 AM, Junior wrote:

> If you listen close enough you can tell the difference by ear.
> Find one of each on the air which is strong and no noise present.

Charles, you are wrong.  You can generate an AFSK signal to look on  
the spectrum precisely like an RF generated FSK signal.

Except that you can do better with AFSK than you can with FSK since it  
is much easier for you and I to implement proper wave shaping in AFSK  
than we can do in FSK -- in most cases, you have zero control over how  
the manufacturer has implemented FSK.

AFSK just means that you are generating a frequency shifted signal at  
a frequency that is in the "audio" range and then shifting  
(modulating) it through a balanced modulator.  In the modern world, a  
quadrature base band signal is shifted using using a quadrature  
sampling exciter -- in fact, the "A" in AFSK can be anywhere from DC  
to a couple of hundred kiloHertz.

73
Chen, W7AY

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