In an SSB rig, if the two signals in question are 1.7 dB apart, the AGC
voltage developed will be a combination of the two, with the
larger signal responsible for a slightly larger portion of the
total. The signals will still be 1.7dB apart after
detection, hardly a capture effect. Conversely, in an FM system, where detection
is highly non-linear with respect to amplitude, a small diference in
signal strength (on the order of several dB) will manifest itself
as one signal appearing at the output of the detector with the slightly
weaker signal being totally suppressed. You can hear this on the FM
broadcast band during a tropo-duct when one station which was clearly
audible will suddenly disappear as another more distant station "phpts"
in to replace it when its signal exceeds the capture threshold.
This having been said, I would agree with Pete's statement below
that although the 1.7dB advantage is probably hard to detect with
the ears, it should yield a slight statistical advantage over time.
As long as the 1.7dB advantage is obtained without violating the
rules, then more power to the louder guy (pun intended).
73 de Mike, W4EF........
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From: Pete Smith[SMTP:n4zr@contesting.com]
Sent: Saturday, August 08, 1998 10:21 PM
To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Re: Power Level?
At 02:55 PM 8/8/98 EDT, AD6E@aol.com wrote:
...
> Can you really notice (or will your RX
>"capture") a signal that is 1.7 dB stronger than another? Certainly in the
>realm of high tech digital communications thats significant and measurable.
>In FM communications, thats barely enough to "capure". But in the ear? Give
>me a break.
I don't think I buy Paul's argument about AGC differentiating between two
signals 1.7 dB apart, but I *am* convinced that averaged over the course of
a contest, 1.7 dB makes a significant difference, just as surely as you
can't argue in any single QSO, that 1.7 dB more power made THE difference.
But over 24 or 48 hours, X stations just above the noise floor that
wouldn't have been workable otherwise, Y minutes saved by getting out of
pileups just marginally quicker on the average, etc. Makes a bigger
difference in some contests than in others, but it's always there ...
73, Pete Smith N4ZR
n4zr@contesting.com
"That's WEST Virginia. Thanks and 73"
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