Chris Peterson wrote:
>All,
>
>Many times I've read here that you can't hear the difference between 3DB.
>
>Many have used this argument to claim that an antenna with 3DB more gain is
>somehow not necessary, or that someone should only run 50 watts rather than
>100 watts because nobody will know the difference.
>
>I've been fighting with a weak Micor receiver for the past few months and
>have come up with some theories on why you can, or can't, hear 3DB depending
>on the circumstances. I'm curious to know if anyone agrees, or disagrees,
>with me.
>
>First, the receiver I'm using is about 7DB down from where it should be.
>I've noticed that it hears an HT fine from my home using 5 watts. However,
>it can not hear the same HT at 2.5 watts, a difference of 3DB.
>
>I think this must have something to do with the receiver's AGC. My thought
>is, that since the receiver is weak, the AGC is cranked all the way open,
>partially compensating for the receiver's weakness. However, since the AGC
>is cranked, there is no where for it to go when the signal gets weaker.
>
Micor? AGC? A Micor receiver doesn't have AGC. It might have AFC, and
for some of the reasons given the symptoms could be similar.
>This makes picket fencing more pronounced, and makes the system less usable
>for HT users with already weak signals.
>
>Now let's say I retune the receiver to correct the problem. I should be
>able to work the repeater on 2.5 watts, or 5 watts, without hearing a
>perceptible change in signal strength. Am I warm so far?
>
Not really. In FM, you wouldn't 'correct' for an over abundance of
signal. In fact, most FM receivers already have an over abundance of
gain in the latter stages. A limiter that is saturated usually produces
a quieting output, which is desired. The limiter limits all signals to
the same amplitude level to minimize (am) noise interference. While
receivers might exist that have a control for their gain, the Micor
isn't one of them. Most FM receivers have a set amount of gain to each
stage, and the net result is quiet a bit no matter the level of the
incoming signal.
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