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Author Topic: Ultra Linear RF operation  (Read 1660 times)
G3RZP
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Posts: 983




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« on: August 25, 2015, 12:58:52 AM »

Needing to look something up in old (1963) copies of the RSGB Bulletin, one thing that caught my eye was a linear amplifier in 'Ultra linear' mode. It used a cathode driven, RF grounded grid, 813 with 1200 volts on the anode  and 450 volts on the screen. The unusual approach I have seen nowhere else is that there is an overwind on the anode feed choke, which is in series with screen grid such that instantaneous screen voltages is modulated by, and in phase with, the RF anode voltage, in the same way as the screen volts in an ultra linear audio amplifier is. The author (G3MHQ) claimed to get 250 or so watts PEP output with 50 to 75 watts of drive before flat topping occurred. He also used two 140pF caps ganged for the input tuning of the pi with the ten metre coil between them to keep the strays down on 10.

But  has anybody seen any articles or papers recommending the same thing, and any ideas and why how good (or otherwise) is it likely to be? Of course, back then, few people had spectrum analysers, and some then said the G2DAF circuit sounded good!
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