Hi Reggie,

As we say here .... BINGO !!!, you are right the fraction is proportional
and enough accurate for practical purpouses.
I need the calculation of the SQRT(REF / FWD) only to show it in the LCD at
end of the TUNE JOB.
In each iteration, I only read the FWD and REF looking for the Maximun FWD
Value and the Minimun REV Value, at this time the SQRT calculation is only
to show it in the LCD.

Regards,

Augusto

----- Original Message -----
From: "Reggie Berdin" <rberdin@MYREALBOX.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, August 24, 2003 11:43 PM
Subject: Re: [PIC:] Square root 16bit number


> Hi Augusto,
>
> I have previously made digital RF meters using Motorola 6805 mcu years
ago.
>
> SWR is easily calculated as:
>
> SWR = (FWD+REF)/(FWD-REF)
>
> FWD and REF are direct ADC voltage readings on the swr bridge.  The
readings
> are already proportional to the SQRT of the POWER.  So you don't need to
use
> a square root function.
>
> regards,
> Reggie
>
> ----- Original Message -----
> From: "CVT-SSS" <cvt@CVT-SSS.COM>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Monday, August 25, 2003 5:15 AM
> Subject: Re: [PIC:] Square root 16bit number
>
>
> > The original message was:
> >
> > Hi to all,
> >
> > I4m just making an RF sensor with a PIC16F877A, reading Forward RF
>  ( FWD )
> > in AN0 and Reverse RF ( REV) in AN1 ports.
> > I have a max value of 1024 * ( 4.5 Volts / 5 Vots Ref. ) in each port,
> > giving me a max value of  921 in each case.
> > I need to get the value of the following formula:
> >
> > SWR = 100 * (( 1 + C ) / ( 1 - C ))
> >
> > where
> >
> > C = SQRT( REV / FWD )
> >
> > Question is how to calculate the square root of  ( REV / FWD ) ?
> >
> > I was trying to develop a sum of series to get the SQRT but it is not
> enough
> > accurate and interpolation method is too slow.
> >
> > Some ideas ?
> >
> > Regards,
> >
> > Augusto
> >
>
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