[RTTY] Fw: ARLB006 NTIA: No Objection to Additional Data Modes on60 Meters [now another FSK/AFSK thread]

[Kok Chen]

On Mar 30, 2012, at 9:56 AM, Ed Muns wrote:

>  FSK requires a homebrew or commercial
> interface and AFSK (with respects to Uncle Bill's history lesson!) requires
> proper adjustments of drive level, compression off, etc.

I have clarified the AFSK nomenclature with Uncle Bill in private e-mail last night.

What most of us today call "AFSK" can rightly be called SSB-AFSK.

Basically, if you take what Bill calls AM-AFSK, remove the AM carrier and one of the AM sidebands, you get precisely what we call an RTTY signal (i.e., two alternating FSK carries in the RF spectrum).  The removal of the carrier and one of the AM sidebands from the spectrum is what an SSB transmitter does.

When you plug an audio FSK signal (i.e., two tones in the audio range, for example 2125 Hz for Mark and 2295 Hz for space) into an FM transmitter, you get what Bill calls FM-AFSK (yes, that nomenclature is quite common).  When you plug the same audio signal into an AM transmitter and you get AM-AFSK.  And finally, when you plug the same audio signal into an SSB transmitter and you get good old steam RTTY.  (It is all in the Convolution Theorem.)

The FM-AFSK and AM-AFSK modes are sub-carrier systems (probably designated as F2D emission mode; but I am not 100% certain and I don't *think* that they are ham legal in the US below 28 MHz), but "SSB-AFSK" is nothing more or less than an F1B emission mode signal.

So folks, at least in my opinion, it is OK to use the term AFSK to describe the process of injecting an audio FSK ("AFSK") signal into an SSB transmitter to produce RTTY.  The pedant might want to call it SSB-AFSK, but it is mathematically an AFSK process.  I don't mind calling "FM-AFSK" as simply "AFSK" either; because it is.

73
Chen, W7AY