[600MRG] FT Question Answered?

[Ben Gelb]

I think what you are describing is distortion in the audio chain. That
seems like a problem even with linear amplification (though maybe nonlinear
would make it worse) ... I don't know that your comments really apply to
modern equipment and AFSK techniques, though... audio should be pretty
clean (and needs to be in order to control occupied bandwidth).

73 de N1VF

On Jan 14, 2018 7:07 AM, "Bill Cromwell" <wrcromwell at gmail.com> wrote:

> Hi John,
>
> Consider that Collins and others used a single audio tone to generate a CW
> signal in some of their SSB transmitters. In theory it is wonderful. It is
> less expensive. It actually seems to work as *theory* says it should. They
> dropped it because it did not *reliably* give a clean signal..even with
> 'linear' amplifier chains.
>
> I understand that the shift is small for the newfangled digital modes but
> shift they do. It is not a single tone and then later another single tone.
> Use caution if you are going to add nonlinear amplifiers into the mix.
>
> 73,
>
> Bill  KU8H
>
> On 01/13/2018 03:45 PM, John Andrews wrote:
>
>> 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>
>>>>
>>>> _______________________________________________
>>>> 600MRG mailing list
>>>> 600MRG at w7ekb.com
>>>> http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
>>>>
>>>>
>>>
>> _______________________________________________
>> 600MRG mailing list
>> 600MRG at w7ekb.com
>> http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
>>
>
> --
> bark less - wag more
>
> _______________________________________________
> 600MRG mailing list
> 600MRG at w7ekb.com
> http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
>