[GreenKeys] True FSK vs AFSK

[Bob kb8tq]

Hi

AFSK = Audio modulation of a carrier with all the sidebands present. 

FSK = One of only two tones with no carrier and no opposite sidebands. 

You can generate this or that a number of ways. What counts in terms of 
calling it this or that sort of modulation is the signal that hits the antenna. 
Unless it has a carrier with tones spaced off of it (either as FM or AM) it
technically isn’t AFSK. 

This is nice because you can’t use AFSK on some pretty important chunks
of the spectrum ….

If you want to go a bit nuts, you can look at FSK as a pair of 100% modulated
ASK (amplitude shift key) signals, each chugging along. No ASK is not 
the same as AFSK.

Bob

> On Feb 4, 2022, at 1:54 PM, Paul Kasley <w9ts at comcast.net> wrote:
> 
> Don't know. I feed audio from my compy into my K3. DDS chips are easily shifted. And way back, I switched a cap in and out of the VFO of my AM-only DX100.
> 
> Agreed, more sophisticated digital modes require audio generation and processing.
> 
> Simply responding to the original question as posed - yes, there can be a benefit to FSK v AFSK.
> 
> -w9ts
> 
> On 2/4/2022 12:42, Jim Haynes wrote:
>> On Fri, 4 Feb 2022, Paul Kasley wrote:
>>> 
>>> Directly shifting a carrier oscillator eliminates the audio chain and is
>>> essentially CW.
>> 
>> However, is that the way modern radios actually generate FSK?  and CW?
>> Or do they actually generate AFSK internally and put it into the audio
>> chain?
>> 
>> And, given that we have dozens of digital modes these days that all begin
>> by generating audio frequency signals, is AFSK for FSK any worse than
>> any other digital mode?
>> 
>> Granted that it's possible, easy in fact, to generate crud on the air by
>> feeding audio into the SSB transmitter.
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