Equipment Reviews, January 2000
RF Systems P-3 Preselector
I jumped at the chance to review this unit when Fred Osterman of Universal Radio gave me the opportunity, having been alerted by a mention on Radio Nederland’s website that the P-3 was on the way. Why all the excitement about another black box? Because the one fault of modern receivers is their lack of front-end selectivity.
Back in the old days before digital frequency synthesizers, most quality radios had a tunable radio frequency amplifier as the first stage after the antenna input. This amplifier was tuned either in conjunction with the main tuning or, in some radios, the stage was tuned with a separate “preselector” control. The main reason that this stage was required was to reduce the problem of “images”-signals that were twice the intermediate frequency away from the desired signal. With the advent of high (>30 MHz) first IFs, image rejection could be accomplished by a simple low pass filter at the front end of the receiver. Along with the switch to digital frequency synthesis and equipment minaturization, mechanical parts such as variable capacitors, wafer switches and slug-tuned inductors became expensive and difficult to obtain. As a result, the tuned front-ends of yore were replaced with fixed bandpass filters covering an octave or more, or no filtering at all.
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