[GreenKeys] HAL ST-6 Manual needed

[Ralph Mowery]

In theory there is no difference in what comes out of the transmitter.  For all practical purposes there isn’t  any.  Depending on how much carrier suppression and how clean the audio tones are, there is a slight difference.  You do get a carrier (just like in ssb) but it is so far down it is lost in the noise.  I tend to think of this like putting another brick on a dump truck load of them.  You know it is there, but unless you spend the time to actually count the bricks you never know it.   That is the way with most electronics.   You know it is there, but for all practical purposes it is not.

 

The stages in a transmitter can be class C after the afsk in the ssb transmitter, but it is not easy to do in most transmitters.

 

I think we are saying the same thing.

 

My question is how is the FSK being generated in most of the transceivers that have the rtty position on the mode switch.   Do they more or less go into the CW mode and actually switch the carrier or do they do something else ?

Along the same lines do they change the bias on the amplifier stages to go from linear to class C. when in rtty or CW ?

 

 

From: Nick England [mailto:navy.radio at gmail.com] 
Sent: Thursday, October 20, 2016 10:42 AM
To: Ralph Mowery
Cc: Greenkeys
Subject: Re: [GreenKeys] HAL ST-6 Manual needed

 

I know that Collins S-line transmitters (and I'm sure others) use a keyed audio tone to generate CW. In an SSB transmitter, any RF signals at the transmitting frequency must be generated by audio tones. Otherwise it isn't an SSB transmitter.

I may be dense, but I fail to see any difference between SSB AFSK and "true FSK" (assuming a single TTY signal). Isn't the output of the transmitter exactly the same? In either case, the output alternates between two signals 170 Hz apart. Using FSK vs AFSK might change the reading on your frequency dial, but that is trivial. 

With "true FSK" you can use class C amplifier stages in the transmitter chain vs linear amplifier stages found in an SSB rig, so the "true FSK" transmitter can be more efficient, but that means you need a separate transmitter for RTTY and another one for SSB voice.

 

AM transmitters with FSK have a separate FSK keyer that mixes the shift pair with the VFO/crystal to generate the transmitted signal - the audio modulator is turned off. Back in the olden days I think AFSK on AM was used mainly at UHF where equipment wasn't accurate/stable enough for FSK.

n.b. One advantage of AFSK SSB is that you can run multiple tone pairs for frequency-division multiplex of multiple TTY signals, but hams don't do that...

 

Cheers


Nick England K4NYW

www.navy-radio.com

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