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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