My apology to Jim and the reflector for my last posting. Guess I'm a little
grumpy today. Rigs for a long time have been designed for FSK RTTY, meaning
that a frequency-shifted carrier was transmitted and/or AFSK RTTY, meaning
a two-toned SSB signal was generated. Both imply very different transmit
processing. We're on a Ten-Tec reflector where what I've just stated is
true up through the Orion's. I can't vouch for some of the later rigs, but
suspect the same is true. As for other-branded semi- or full-SDR
implemented radios, your mileage may vary. If Jim wants to describe a
frequency-shifted carrier as modulation and treat it as an analog signal,
fine, then run a Class A amp with it if you like. However, my point was
that generating a clean signal via FSK is a lot easier, usually, than AFSK
where many more variables enter into the equation. Today, with SDR and
semi- or partial-SDR radios, it's anyone's guess on how the RTTY signal is
being generated, but it's still up to the operator to generate a clean
signal.
73, Duane
Duane Calvin, AC5AA
Austin, Texas
www.ac5aa.com
-----Original Message-----
From: Duane Calvin [mailto:ac5aa1@gmail.com]
Sent: Monday, September 22, 2014 1:12 PM
To: 'k9yc@arrl.net'; 'Discussion of Ten-Tec Equipment'
Subject: RE: [TenTec] Argo V and digital modes
Interesting - your response sounded as simple-minded as mine. But then, I
agree, I'm simple-minded.
73, Duane
Duane Calvin, AC5AA
Austin, Texas
www.ac5aa.com
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Monday, September 22, 2014 11:26 AM
To: tentec@contesting.com
Subject: Re: [TenTec] Argo V and digital modes
On Mon,9/22/2014 8:18 AM, Duane Calvin wrote:
> Well, strictly speaking, RTTY generated via FSK is a carrier mode,
however,
> RTTY generated via AFSK is an analog mode and still requires care to
> preserve linearity.
That's a simple-minded (and incorrect) view of AFSK and FSK. Regardless
of how RTTY is transmitted, there is modulation, and modulation produces
sidebands, both from the modulation waveform and from distortion
produced by that waveform due to distortion in the RF chain. The only
difference with AFSK is that it's possible to add distortion from the
audio chain, and that one must pay attention to setting audio levels.
Conventional wisdom is that FSK is cleaner. Until Elecraft worked on it
(in firmware), FSK had wider keying sidebands than AFSK in the K3. Don't
assume that your rig is better. :)
73, Jim K9YC
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