This message is in MIME format. Since your mail reader does not understand
this format, some or all of this message may not be legible.
------_=_NextPart_001_01C05E0F.85965040
Content-Type: text/plain
Steve, what must be gaurded against is overheating of the transistor.
Overheating is related to load mismatch and thermal time constant of the
transistor. If you look at a typical transient thermal response graph for a
transistor you will see that the die has a typical response of 10ms or so.
So if you can react quicker than this (say in about 1ms) then you can
adequately protect the transistor. They do not instantaneously vaporize
under adverse load conditions. Therefore simultaneous detection of forward
and reflected power is unnecessary, and a single A/D converter is typically
used. What must be checked however, is that the ALC response time of the
amplifier is this quick if that's the method used for shutdown under high
SWR conditions. Severe load mismatches can cause the transistors to see
higher voltages, but typically not as high as the breakdown rating of the
device.
--Dave
K0QE
> -----Original Message-----
> From: Steve [SMTP:ve3tu@rac.ca]
> Sent: Sunday, December 03, 2000 8:15 PM
> 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
>
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
------_=_NextPart_001_01C05E0F.85965040
Content-Type: text/html
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Dus-ascii">
<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
5.5.2650.12">
<TITLE>RE: [AMPS] SWR Protection</TITLE>
</HEAD>
<BODY>
<P><FONT COLOR=3D"#0000FF" SIZE=3D2 FACE=3D"Arial">Steve, what must be =
gaurded against is overheating of the transistor. Overheating is =
related to load mismatch and thermal time constant of the transistor. =
If you look at a typical transient thermal response graph for a =
transistor you will see that the die has a typical response of 10ms or =
so. So if you can react quicker than this (say in about 1ms) then you =
can adequately protect the transistor. They do not instantaneously =
vaporize under adverse load conditions. Therefore simultaneous =
detection of forward and reflected power is unnecessary, and a single =
A/D converter is typically used. What must be checked however, is that =
the ALC response time of the amplifier is this quick if that's the =
method used for shutdown under high SWR conditions. Severe load =
mismatches can cause the transistors to see higher voltages, but =
typically not as high as the breakdown rating of the device. =
</FONT></P>
<BR>
<P><FONT COLOR=3D"#0000FF" SIZE=3D2 FACE=3D"Arial">--Dave</FONT>
<BR><FONT COLOR=3D"#0000FF" SIZE=3D2 FACE=3D"Arial">K0QE</FONT>
</P>
<BR>
<UL>
<P><FONT SIZE=3D1 FACE=3D"Arial">-----Original Message-----</FONT>
<BR><B><FONT SIZE=3D1 FACE=3D"Arial">From: </FONT></B> <FONT =
SIZE=3D1 FACE=3D"Arial">Steve [SMTP:ve3tu@rac.ca]</FONT>
<BR><B><FONT SIZE=3D1 FACE=3D"Arial">Sent: </FONT></B> <FONT =
SIZE=3D1 FACE=3D"Arial">Sunday, December 03, 2000 8:15 PM</FONT>
<BR><B><FONT SIZE=3D1 =
FACE=3D"Arial">To: </FONT></B> <FONT SIZE=3D1 =
FACE=3D"Arial">amps@contesting.com</FONT>
<BR><B><FONT SIZE=3D1 =
FACE=3D"Arial">Subject: </FONT>=
</B> <FONT SIZE=3D1 FACE=3D"Arial">[AMPS] SWR Protection</FONT>
</P>
<BR>
<P><FONT SIZE=3D2 FACE=3D"Arial">If anyone is interested visit this =
site</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"><A =
HREF=3D"http://www.ibelings.com/n4ip/sskw/"; =
TARGET=3D"_blank">http://www.ibelings.com/n4ip/sskw/</A> It =
describes the</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">problem of using a microprocessor =
with a single ad</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">converter to calculate swr. The 30 =
usec delay between</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">reads to too long to get a snapshot =
of pf and pr to</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">calculate swr correctly. I plan to =
shut down the amp if</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">the pf goes above a certain level =
which could be caused by</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">hi drive or high swr and I plan to =
shut down the amp if</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">the pr goes above a certain level and =
then the</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">microprocessor will calculate the swr =
and shut the amp</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">down if the calculated swr is too =
high. This routine</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">covers all the possibilities. My =
original question was if</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">anyone knows of an ad chip or =
microprocessor that has</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">separate ad converters in it to take =
simultaneous readings</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">of the pf and pr . If there is no =
such animal then the</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">next best thing is to use two ad =
converters triggered to</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">read at the same time. I didn't mean =
to stir up the pot</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">with such a simple question.</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">73 Steve</FONT>
</P>
<BR>
<P><FONT SIZE=3D2 FACE=3D"Arial">--</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">FAQ on =
WWW: &n=
bsp; <A HREF=3D"http://www.contesting.com/FAQ/amps"; =
TARGET=3D"_blank">http://www.contesting.com/FAQ/amps</A></FONT>
<BR><FONT SIZE=3D2 =
FACE=3D"Arial">Submissions: &nb=
sp; amps@contesting.com</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">Administrative requests: =
amps-REQUEST@contesting.com</FONT>
<BR><FONT SIZE=3D2 =
FACE=3D"Arial">Problems: =
=
owner-amps@contesting.com</FONT>
</P>
</UL>
</BODY>
</HTML>
------_=_NextPart_001_01C05E0F.85965040--
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|