Steve:
Without reading that site in complete detail, I believe he's saying that he
used a MAX-186 12 channel a/d converter connected to a Basic Stamp. This
is an 8 channel multiplexed a/d converter. He converts 24 times per second
(same a/d, multiple channels) and builds up peak values for Pf and Pr. He
then computes the VSWR and trips things out if he gets above 1.7:1. My
guess is that this arrangement is able to shut things down before they get
too far out of control (or - before the smoke is let out of the
transistors.)
This method works well. It's true that you need to capture the two signals
together when you have a dynamically changing signal like SSB ("together"
being defined as faster than the two signals are changing!). The software
peak detectors take care of that problem nicely.
If you really want to use simultaneous readings, I would probably do it
with two a/d converters. This would achieve your goal. Analog Devices has
a wide range of suitable converters and they sample fairly liberally.
Or, use N4IP's approach - or (sorry for the shameless plug) get one of our
meters... we use a similar method using an 11 MHz PIC.
73
Bruce R. Knox
RF Applications, Inc.
-----Original Message-----
From: Steve [SMTP:ve3tu@rac.ca]
Sent: Sunday, December 03, 2000 22:15
To: amps@contesting.com
Subject: [AMPS] SWR Protection
If anyone is interested visit this site
http://www.ibelings.com/n4ip/sskw/ It describes the
problem of using a microprocessor with a single ad
converter to calculate swr. The 30 usec delay between
reads to too long to get a snapshot of pf and pr to
calculate swr correctly. I plan to shut down the amp if
the pf goes above a certain level which could be caused by
hi drive or high swr and I plan to shut down the amp if
the pr goes above a certain level and then the
microprocessor will calculate the swr and shut the amp
down if the calculated swr is too high. This routine
covers all the possibilities. My original question was if
anyone knows of an ad chip or microprocessor that has
separate ad converters in it to take simultaneous readings
of the pf and pr . If there is no such animal then the
next best thing is to use two ad converters triggered to
read at the same time. I didn't mean to stir up the pot
with such a simple question.
73 Steve
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