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Thanks for the response Dave. The primary reason is to shut down the amp
as fast as possible and second is to calculate true swr instantaneously.
Like you say you can do it with software but I have a LDG antenna tuner
for mobile use that uses the 68hc11 chip and it cannot tune up on a ssb
signal just a cw tx signal only because the processor cannot follow the
ssb signal and the transmitter changes the output as the tuner tries to
find a match. As in this case fast is not fast enough. I guess the moral
of the story is to use cheap fets instead of expensive ones hi hi.
tu es 73 Steve
Dave D'Epagnier wrote:
>
>
> 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
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
>
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Thanks for the response Dave. The primary reason is to shut down the amp
as fast as possible and second is to calculate true swr instantaneously.
Like you say you can do it with software but I have a LDG antenna tuner
for mobile use that uses the 68hc11 chip and it cannot tune up on a ssb
signal just a cw tx signal only because the processor cannot follow the
ssb signal and the transmitter changes the output as the tuner tries to
find a match. As in this case fast is not fast enough. I guess the moral
of the story is to use cheap fets instead of expensive ones hi hi.
<p> tu es 73 Steve
<p>Dave D'Epagnier wrote:
<blockquote TYPE=CITE>
<p><font face="Arial"><font color="#0000FF"><font size=-1>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:</font></font></font>
<p><font face="Arial"><font color="#0000FF"><font size=-1>SWR =
(1+SQRT(Pr/Rf))/(1-SQRT(pR/pF))</font></font></font>
<p><font face="Arial"><font color="#0000FF"><font size=-1>Trip the relay
if the SWR is too high.</font></font></font>
<p><font face="Arial"><font color="#0000FF"><font size=-1>The whole operation
could be performed in less than 1ms.</font></font></font>
<p><font face="Arial"><font color="#0000FF"><font
size=-1>--Dave</font></font></font>
<br><font face="Arial"><font color="#0000FF"><font
size=-1>K0QE</font></font></font>
<ul><font face="Arial"><font size=-2>-----Original Message-----</font></font>
<br><b><font face="Arial"><font size=-2>From: </font></font></b>
<font face="Arial"><font size=-2>Steve [SMTP:ve3tu@rac.ca]</font></font>
<br><b><font face="Arial"><font size=-2>Sent: </font></font></b>
<font face="Arial"><font size=-2>Friday, December 01, 2000 10:03
AM</font></font>
<br><b><font face="Arial"><font
size=-2>To: </font></font></b>
<font face="Arial"><font size=-2>amps@contesting.com</font></font>
<br><b><font face="Arial"><font
size=-2>Subject: </font></font></b>
<font face="Arial"><font size=-2>[AMPS] SWR Protection</font></font>
<p><font face="Arial"><font size=-1>Talking about more interesting aspects
of amps, I was wondering if</font></font>
<br><font face="Arial"><font size=-1>anyone knows of a single chip
microprocessor
or pic that has 4 or 8 A/D</font></font>
<br><font face="Arial"><font size=-1>converters in the chip that can monitor
4 input simultaneously. I am</font></font>
<br><font face="Arial"><font size=-1>planning on building a swr protection
board for a solid state amp using</font></font>
<br><font face="Arial"><font size=-1>a 68hc11 chip that has a single A/D
converter that has selected inputs.</font></font>
<br><font face="Arial"><font size=-1>It takes 32 micro seconds to do each
conversion so you don't really get</font></font>
<br><font face="Arial"><font size=-1>a snapshot of the forward and reflected
power at the same time. I know</font></font>
<br><font face="Arial"><font size=-1>the you can fudge it with software
and get it close but I an interest in</font></font>
<br><font face="Arial"><font size=-1>simultaneous reading on the A/D input
or a simple outboard A/D chip</font></font>
<br><font face="Arial"><font size=-1>would do.</font></font>
<p><font face="Arial"><font size=-1>tu es 73 Steve VE3TU</font></font>
<p><font face="Arial"><font size=-1>--</font></font>
<br><font face="Arial"><font size=-1>FAQ on
WWW:
<a href="http://www.contesting.com/FAQ/amps";
TARGET="_blank">http://www.contesting.com/FAQ/amps</a></font></font>
<br><font face="Arial"><font
size=-1>Submissions:
amps@contesting.com</font></font>
<br><font face="Arial"><font size=-1>Administrative requests:
amps-REQUEST@contesting.com</font></font>
<br><font face="Arial"><font
size=-1>Problems:
owner-amps@contesting.com</font></font></ul>
</blockquote>
</html>
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FAQ on WWW: http://www.contesting.com/FAQ/amps
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Administrative requests: amps-REQUEST@contesting.com
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