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Re: [Amps] Solid State Amps

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Subject: Re: [Amps] Solid State Amps
From: "Paul Christensen" <>
Date: Fri, 17 Oct 2014 14:56:17 -0400
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- A good active linearization circuit can produce far better linearity than class AB with 10dB of negative feedback, and even better than that of tetrodes.

With a linearizer running as an adaptive predistorter, we can largely dispense with amp class type at least within reasonable limits. Warren Pratt has shown that with APD active in the RF exciter, even class B amplification can produce better linearity than class AB amps, and many class A amplifiers. A linearizer in the exciter with power sampling fed back from the external amp produces maximum linearity as a complete system.

We have this available today, at least with the Apache ANAN series of transceivers. The Zeus ZS-1 uses a manual linearizer but the end result is the same. IMD reduction is not improved by some trivial amount. The improvement is in the order of 30 dB for third-order products.

Under strong signal conditions, I've observed AC2IQ and WA1OXT with completely vertical transmit passband edges. AC2IQ uses an analog linearizer (see his QRZ page) while WA1OXT uses a firmware-based linearizer in his ANAN 100D transceiver. Maximum improvement typically occurs near Fc then gently degrades evenly on both sides of Fc. But maximum reduction occurs where it's needed most: within +/- 10 kHz of Fc. Warren Pratt is working on methods to minimize IMD spectra well away from Fc.

I own a SPE 1KFA SS amp and do not foresee adding another SS amp until: (1) better cooling + noise reduction solutions are developed; and (2) we see better output power regulation with changes in PA deck temperature. This should be something easily managed with internal gain control, but yet I see this power/heat variation with several SS amps.

Paul, W9AC

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