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[AMPS] Tube IMD/6146/4cx10000

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Subject: [AMPS] Tube IMD/6146/4cx10000
From: (
Date: Sat, 20 Feb 1999 13:17:48 -0500

On Fri, 19 Feb 1999 10:58:30 -0000 Peter Chadwick
<> writes:
>Further to Rich's comments, I believe you'll really need negative 
>whatever tube you use. However, you are getting down to looking at 
>levels in the whole exciter.

The TS-830 uses negative feedback Peter. The stock radio measures -35dB
on SSB voice. Driver and PA tube condx is important also.

>To get carrier rejection, the balanced modulator is normally run at a
>reasonably high level of drive, so the IMD can't be neglected there. 
>can the 3td order IMD of the audio stages. Then there's the 
>compressor, and
>all the subsequent signal processing in the tx. Usually, you make the 
>PA the
>dominant IM producer, but if your design spec is -25dB on tone (-31dB 
>PEP), then exciter IMP's of around -35dB to -40dB rel to 1 tone of a 2 
>signal are adequate. If you want -46dB relative to tone out of the 
>you probably will end up limited by the exciter portion before the 
>If signal levels into the SSB filter are around 0dBm, (220mV in 50 
>then you can typically expect about 60dB down IMD products from the 
>alone. Interestingly, my measurements (admittedly some years ago) 
>that you could expect 3rd order products between 60 and 70dB down at 
>rms per tone pretty much regardless of filter impedance - I went from 
>ohms to 2K ohms on a number of filters, and they all tended to turn 
>similar results.

The +10dBM signal out of the transverter port of the TS-830 measures
right around  -50dB IMD. That and the very low phase noise is the reason
I went with the TS-830 as a VHF/UHF IF platform. 

>So there's a real question of how far it's worth going on PA
> any case, IMP's of around 60 dB down could get 
>in the phase noise, as well as the 'wide band' noise of the low level

Is it worth going beyond -40dB on HF ?  Or even -20 during a contest !

73  Carl  KM1H

>Peter G3RZP
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