[Amps] 10 DB increase
David Kirkby
david.kirkby at onetel.net
Sat Feb 5 09:34:01 EST 2005
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/
More information about the Amps
mailing list