The formulas - as stated - are simple ratios, and will determine delta dB
between two voltages or two power levels when they are the only variables.
There are no other variable in those equations. If you assume other
variables, then the equations must be modified to accomodate them
Al - K8EUR
----- Original Message -----
From: "Bill L. Fuqua" <wlfuqu00@uky.edu>
To: <al.dolgosh@hamradio.org>
Cc: <on4kj@skynet.be>; <david.kirkby@onetel.net>; <realex@flash.net>;
<amps@contesting.com>
Sent: Saturday, February 05, 2005 11:41 PM
Subject: Re: Re: [Amps] 10 DB increase
> They are only the same only if input and load resistances are the
same. When these resistances are not equal the 20log Vo/Vi is usually
used. An example would be the gain of an audio interstage amplifier or an
Audio power amplifier which would have perhaps 1k input resistance and
perhaps 4 or 8 ohm load resistance.
>
> 73
> Bill wa4lav
>
>
> -----Original Message-----
> From: "Radioal" <al.dolgosh@hamradio.org>
> To: "hermans" <on4kj@skynet.be>, "'David Kirkby'"
<david.kirkby@onetel.net>, "'Bob Alexander'" <realex@flash.net>
> Date: Sat, 5 Feb 2005 18:33:33 -0500
> Subject: Re: [Amps] 10 DB increase
>
> 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
> > Envoyà : samedi 5 fÃvrier 2005 14:34
> > Ã : 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/
> >
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|