Absolutely agreed, Dave.
For microprocessor coding using integers, there is an easier algorithm that
leaves out the square root (and makes it compute WAY faster):
((Forward A/D + Reflected A/D) * 100) / (Forward A/D - Reflected A/D) = VSWR *
100
so, for example, a VSWR of 2.3:1 would yield 230.
This is how our wattmeters do it.
Bruce R. Knox W8GN
RF Applications, Inc.
-----Original Message-----
From: Dave D'Epagnier [SMTP:DAVED@ctilidar.com]
Sent: Friday, December 01, 2000 12:17
To: Steve; amps@contesting.com
Subject: RE: [AMPS] SWR Protection
<< File: ATT00000.html >> Steve, why do you want to know the instantaneous
forward and reflected
power? You really wouldn't need this to implement an effective SWR
protection function, unless you expect that your SWR varies extremely
rapidly which probably is not the case. It should suffice to use one A/D
converter and measure the forward and reflected power at different times and
then do the math. For instance, measure the forward power 10 times at
32us/sample. Then measure the reflected power 10 times at 32uS per sample.
Then average all the forward samples, and the reflected samples for a solid
measurement. Now do the math:
SWR = (1+SQRT(Pr/Rf))/(1-SQRT(pR/pF))
Trip the relay if the SWR is too high.
The whole operation could be performed in less than 1ms.
--Dave
K0QE
> -----Original Message-----
> From: Steve [SMTP:ve3tu@rac.ca]
> Sent: Friday, December 01, 2000 10:03 AM
> To: amps@contesting.com
> Subject: [AMPS] SWR Protection
>
>
> Talking about more interesting aspects of amps, I was wondering if
> anyone knows of a single chip microprocessor or pic that has 4 or 8 A/D
> converters in the chip that can monitor 4 input simultaneously. I am
> planning on building a swr protection board for a solid state amp using
> a 68hc11 chip that has a single A/D converter that has selected inputs.
> It takes 32 micro seconds to do each conversion so you don't really get
> a snapshot of the forward and reflected power at the same time. I know
> the you can fudge it with software and get it close but I an interest in
> simultaneous reading on the A/D input or a simple outboard A/D chip
> would do.
>
> tu es 73 Steve VE3TU
>
>
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