[Amps] 10 DB increase

[hermans]

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 at contesting.com [mailto:amps-bounces at contesting.com] De
la part de David Kirkby
Envoyé : samedi 5 février 2005 14:34
À : Bob Alexander
Cc : amps at 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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