A simple sine wave is called a tone, even when it is a radio frequency
sine wave. So CW and FSK both send a single RF tone. With FSK the tone
frequency changes, but at any given time it is just one tone. Yes a tone
IS being transmitted, and no it did not originate as an audio frequency
tone input to a phone transmitter. (although some rigs do generate CW
that way.)
With only one tone there can be no intermodulation distortion, at least
not that will pass through the bandpass filters in a normal transmitter.
Any intermodulation distortion products would be separated by an amount
equal to at least the operating frequency. For example there could be
intermod products of the fundamental and the second or other higher
harmonics.
Perfectly sinusoidal AFSK tones sent by a perfect SSB transmitter, with
perfect level settings would be indistinguishable from "real FSK." In
the real world that perfection is never achieved. The AFSK tones are not
perfectly sinusoidal, the SSB transmitter has some carrier and opposite
sideband leakage, so there can be some IMD.
DE N6KB
On 2014-09-22 14:39, Robert wrote:
> Real FSK is the carrier being shifted between two frequencies, thus Frequency
> Shift Keying. There is no tone being transmitted. AFSK is two audio tones
> being transmitted, thus Audio Frequency Shift Keying.
>
> Bob, K4TAX
>
> Sent from my iPhone
>
>> On Sep 22, 2014, at 6:42 PM, ken.d.brown@hawaiiantel.net wrote: If you use
>> what I call "real FSK" there is only one tone being sent at any one time.
>> There is no carrier that needs to be suppressed as in AFSK to a rig in SSB
>> mode. There is only one tone so there cannot be any intermodulation. Then
>> you can run your gain stages in class C and have class C efficiency. DE N6KB
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