[GreenKeys] True FSK vs AFSK

[Paul Kasley]

And then there is my 60's vintage Collins KWM2 which makes CW by keying 
an internal audio oscillator...

-w9ts

On 2/4/2022 13:13, Bruce Gentry via GreenKeys wrote:
>
> Do AFSK exciters key between two steadily running oscillators, with 
> some sort of dead space between tones, or do they shift one 
> oscillator? Because of the narrow audio bandwidth of SSB,  many people 
> do not realize the need for the audio to be as distortion free as 
> possible when it reaches the balanced modulator(s). A major advantage 
> of true FSK is that it can be amplified by  class "C", a lot more 
> efficient.
>
>    Bruce Gentry, KA2IVY
>
> On 2/4/22 13:24, Paul Kasley wrote:
>>
>> Distortion products. Feeding audio tones into the mic jack of an SSB 
>> tx can result in splatter due to overdrive, and there will normally 
>> be some level of spurs generated by non-linearities in the signal 
>> chain. Plus any junk on the input signal itself gets translated to 
>> the RF.
>>
>> Directly shifting a carrier oscillator eliminates the audio chain and 
>> is essentially CW.
>>
>> -w9ts
>>
>> On 2/4/2022 10:55, Ralph Mowery wrote:
>>>
>>> The only thing I can think of is that AFSK is usually easily to hook up.
>>>
>>> I really hate the term AFSK unless used in an AM or FM transmitter.  
>>> The results of feeding a single audio tone one at a time as in RTTY 
>>> into the SSB transmitter is still FSK .
>>>
>>> I have not checked the FCC rules lately, but below 10 meters true 
>>> AFSK (as in AM of FM) is not legal.
>>>
>>> Ralph ku4pt
>>>
>>> *From:*greenkeys-bounces at mailman.qth.net 
>>> [mailto:greenkeys-bounces at mailman.qth.net] *On Behalf Of *Jeff G
>>> *Sent:* Friday, February 04, 2022 11:36 AM
>>> *To:* GreenKeys at mailman.qth.net
>>> *Subject:* [GreenKeys] True FSK vs AFSK
>>>
>>> Me and a ham club buddy were discussing this yesterday, so I'll 
>>> throw the question to the wolves; in regards to RTTY, is there any 
>>> benefit to doing true FSK on a modern radio vs AFSK?
>>>
>>> Jeff KC3GJX
>>>
>>>
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