>
>I used to work on HF transmitters for the Navy. Military transmitters
>have
>to meet the following standards:
>
>You test the transmitter by injecting two tones on ssb - 1000 and 1625
>Hz.
>
>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.
>Never
>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
>3rd
>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
>couple
>of details wrong...
Do you have any spare 8122's ?
73 Carl KM1H
>
>
>Martin - N3HRT
>
>
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>
>
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