[TenTec] Argo V and digital modes

[Carl Moreschi]

The issue is not IMD, it is sidebands from the transition between the 
two frequencies.  If that is not done carefully, the sidebands can cause 
a wide signal.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 9/23/2014 2:48 PM, ken.d.brown at hawaiiantel.net wrote:
>
>
> There could only be intermodulation distortion caused by the combination
> of those spectral components (the mark tone, the space tone and the
> sidebands) if they were being generated simultaneously. I'm not so sure
> that is the case. The mark tone is only there during mark, the space
> tone is only there during space, and I'm pretty sure the sidebands are
> only there during the transitions. The upper sideband tone occurs in the
> transition when the FSK tone is shifting from the low frequency to the
> high frequency, and the lower sideband tone occurs during the transition
> when the FSK tone is shifting from the higher frequency to the lower
> frequency. Yes there are multiple tones, more than just the mark and
> space tones, but at any instant there is only one. I'd have to be a lot
> better at the math of Fourier transforms to know this for sure, but that
> is the way I think it is.
>
> DE N6KB
>
> On 2014-09-22 18:49, Jim Brown wrote:
>
>> On Mon,9/22/2014 8:38 PM, ken.d.brown at hawaiiantel.net wrote:
>>
>>> You're right about the transients and the sidebands they create. Keyed CW creates sidebands too. I don't think those sideband components could be accurately called intermodulation products though.
>>
>> Hi Ken,
>>
>> I'm not calling the sidebands produced by the transientsIM products. What I'm pointing out is that those sideband components are amplified by the output stage and linear amp, if there is one, and those amp stages generate IM from the combination of those sidebands and the carrier. It's exactly the same mechanism as with CW keying, and with SSB.
>>
>> Those CW spectra in the ARRL reports are the result of the combination of the sidebands, the IM produced by the amplifiers excited by the combination of carrier and sidebands, and the phase noise. Indeed, I've been urging ARRL to use pink noise to drive the mic preamp to produce SSB modulation spectra comparable to the CW spectra, because they combine all three mechanisms.
>>
>> 73, Jim K9YC
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