[AMPS] SWR Protection

Fri, 01 Dec 2000 17:48:43 +0000

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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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<html>
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.
&nbsp;tu es 73 Steve
Dave D'Epagnier wrote:
<blockquote TYPE=CITE>&nbsp;
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
<ul>-----Original Message-----
 From:&nbsp;&nbsp;
Steve [SMTP:ve3tu@rac.ca]
 Sent:&nbsp;&nbsp;
Friday, December 01, 2000 10:03 AM
 To:&nbsp;&nbsp;&nbsp;&nbsp;
amps@contesting.com
 Subject:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
[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:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<a href="http://www.contesting.com/FAQ/amps" TARGET="_blank">http://www.contesting.com/FAQ/amps</a>
 Submissions:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
amps@contesting.com
 Administrative requests:&nbsp; amps-REQUEST@contesting.com
 Problems:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
owner-amps@contesting.com</ul>
</blockquote>
</html>

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--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com