[600MRG] FT Question Answered?

[John Andrews]

Bill,

What you say is correct for speech or any audio that has multiple tones 
<<at the same time>>. But FT8, WSPR, and the vast majority of sound-card 
generated modes only output one tone at a time. In that case, you can 
have non-linear amplifier stages after the SSB signal is generated.

Consider a properly run SSB generator in USB mode at 474.200 kHz. The 
carrier frequency and the LSB are suppressed by maybe 50 dB. If you 
apply a single 1500 Hz tone to the input, you will get a carrier at 
474.200 + 1.500 = 475.700 kHz and nothing else of significance. A 
non-linear amplifier will do no damage to a single frequency signal. No 
magic involved.

So, as long as you avoid the use of simultaneous multi-tone or PSK 
modes, linearity is not required after the SSB generator. FT8 and the 
other "K1JT" modes are all single-tone.

John, W1TAG

On 1/13/2018 1:47 PM, Bill Cromwell wrote:
> Hi Frank,
> 
> That is what I was going to say in reply to your latest query. If you 
> are using audio modulation in upper or lower sideband SSB non linear 
> amps will ruinate and splaterate it.
> 
> 73,
> 
> Bill  KU8H
> 
> On 01/13/2018 10:47 AM, Frank Lotito wrote:
>> I may have answered my question - We use AFSK not direct FSK to 
>> generate modulation modes such as FT8.  AFSK as I recall requires 
>> "linearity" in the audio processing stages.  But once in the RF domain 
>> we can use non-linear devices, such as heterodyne converters, Class E 
>> amps, etc.  Did I get that correct?  73 Frank K3DZ  / WH2XHA
>>
>> Get Outlook for Android<https://aka.ms/ghei36>
>>
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