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Re: [Amps] 10 DB increase

To: "hermans" <on4kj@skynet.be>,"'David Kirkby'" <david.kirkby@onetel.net>,"'Bob Alexander'" <realex@flash.net>
Subject: Re: [Amps] 10 DB increase
From: "Radioal" <al.dolgosh@hamradio.org>
Date: Sat, 5 Feb 2005 18:33:33 -0500
List-post: <mailto:amps@contesting.com>
Thse are the same formulas - one stated in terms of power and one in terms of voltage.

Al - K8EUR
----- Original Message ----- From: "hermans" <on4kj@skynet.be>
To: "'David Kirkby'" <david.kirkby@onetel.net>; "'Bob Alexander'" <realex@flash.net>
Cc: <amps@contesting.com>
Sent: Saturday, February 05, 2005 5:51 PM
Subject: RE : [Amps] 10 DB increase



Any relation between  (G)db = 10.log Po/Pi  and (G)db = 20.log Vo/Vi to
explain the difference between Tx power and Rx S points .....!?

Jos on4kj

-----Message d'origine-----
De : amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] De
la part de David Kirkby
Envoyé : samedi 5 février 2005 14:34
À : Bob Alexander
Cc : amps@contesting.com
Objet : Re: [Amps] 10 DB increase

Bob Alexander wrote:

I went back to the archive to find the original question.
S-meters do not measure received signal level accurately because they
do not
measure the signal but rather the level of the AGC voltage required to
maintain
a constant audio level output.

Most S-neters are adjusted to provide an S9 indication with a specific
input
signal
level at the antenna terminals...usually around 50 uV.  A 10 dB
decrease in
this signal
leaves 15.8 uV at the antenna while a 10 dB increase results in 158 uV
at
the antenna.
Remember we are talking voltage not power.

The AGC/ S-meter system is different in every receiver. Even two
identical
receivers may require a slightly different change in voltage to provide
the
same
degree of AGC action.

With a modern receiver, it would be relatively easy for the manfacturer
to correct for this. An A/D to measure the AGC voltage and a D/A to
drive the meter, with a trivual bit of processing in between. In fact,
it would not even need a processor, as an EPROM or other non-volatile
bit of memory could do it using a lookup table.

Whether you would consider it worth while is another matter, but given
all the bells and whistles on modern equipment, perhaps a calibrated
S-meter would be less useless than some of the other things.



G8WRB

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/



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