[GreenKeys] True FSK vs AFSK

[Bruce Gentry]

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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