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[AMPS] Transceivers high 3rd order IMD

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Subject: [AMPS] Transceivers high 3rd order IMD
From: (
Date: Sat, 20 Feb 1999 13:56:43 -0500
>I used to work on HF transmitters for the Navy. Military transmitters 
>to meet the following standards:
>You test the transmitter by injecting two tones on ssb - 1000 and 1625 
>3rd order IMD -  -38 dB below the two primary tones.
>Carrier suppression has to be -50 dB below the two tones.
>Opposite sideband suppression has to be -50 dB below the two tones.
>Military transmitters are very clean but they waste a lot of power. 
>The amps
>are usually operated class A.
>The transmitters that I worked on had two 8122's driving two 
>4cx1500a's. The
>8122's ran at 320 ma static plate current.
>I think the spec says that max plate current for that tube is 300 ma.  
>understood why they did that. 

The AB1 spec at 2KV is 335ma per tube. In AB2 at 2.5KV it is 400ma. 

Must have had to in order to keep the 
>order IMD below -38 dB...

The stock AB2 NCL-2000 ran -28dB.   With the G3SEK screen regulator and
biased closer to AB1 the amp is now -35dB.

Has anyone measured the optimum levels for an 8877? Absolute best IMD vs
voltage, bias, etc.

>Anyway, Its been ten years since I worked on them... I might have a 
>of details wrong...

Do you have any spare 8122's ?  

73  Carl  KM1H

>Martin - N3HRT
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