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October 17th 13, 09:05 PM
posted to uk.radio.amateur,rec.radio.amateur.boatanchors
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Antenna Trim?
"Ian Jackson" wrote in message
... In message , gareth writes Whilst a common feature of the communications receiver in the past, the antenna trim control no longer appears. Would this be because modern gear expects a 50 ohm pre-matched feed whilst in former times a long wire might come directly to the antenna socket? "Antenna trim" was usually simply a variable shunt capacitor to chassis/earth, and only served to attempt to tune out any inherent antenna inductive reactance (or maybe to provide a bit of independent fine tuning of the input of the RF stage). It was usually associated with a receiver high(ish) impedance antenna input. When the input impedance is low, an antenna trim capacitor will have very little effect. True, but as a trimmer across the RF stage tuning capacitor? |
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