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Dave:
If you have the new AEA CIA-HF, you don't need to do ANY computation, it is
all done for you automatically using its RL measurement capability. I
apologize, you do need to divide by two and subtract a residual reading in
your head.
It also has an outomatic distance to first fault measurement that is easy to
use and interpret.
73/Mike, N7ML
Mktg. Dir.
AEA div. Tempo Research Corp.
k6ll@juno.com wrote:
> This is a repost with a more relevant subject line. Recent
> discussions of feedline losses on a kt34 and recurring
> threads reminded me of this oldie, which I first posted
> about four years ago.
>
> A good thing to do every year or so is to measure your
> feedline losses. If you have an antenna analyzer that reads
> high values of swr with reasonable accuracy, the measurement
> can be done from the comfort of your radio room, without
> disconnecting the antenna.
>
> Attach the analyzer to the feedline in question, with the antenna
> still connected. Tune the analyzer's frequency until you see the
> highest peak in indicated swr on the meter. There will usually
> be several high peaks. Pick the highest one near the high end of
> the analyzer's range.
>
> Plug the peak observed swr into the following equation:
>
> LOSS = 10LOG((SWR+1)/(SWR-1))
>
> For example, if you see a peak swr of 8 at 24 mhz
>
> LOSS = 10LOG(9/7) = 1.09 dB at 24 MHz
>
> Then all you have to do is consult a coax loss chart to see if
> the measured loss is reasonable for the type and length of
> coax being used, and whether it would be cost effective to put up
> new/different coax.
>
> The reason this method works is that almost all antennas present
> a high value of impedance when operated outside their design
> range. This high impedance is a close approximation of an open
> circuit, and the equation above is valid. This idea was
> presented in QST a few years ago, but the author presented a
> graphical, rather than mathematical, solution. I like the mathematical
> solution better, because you don't have to go back and dig up the QST
> article to find the graph.
>
> Some people distrust the accuracy of high value swr readings
> obtained on inexpensive analyzers, and prefer to take
> repeated measurements over several years to detect trends,
> rather than believing the absolute numbers. That's ok too.
> Whenever I have used the above method to measure brand-new coax,
> the results have always agreed closely with expected losses.
>
> Dave Hachadorian, K6LL
> Yuma, AZ
> K6LL@juno.com
>
> ___________________________________________________________________
> You don't need to buy Internet access to use free Internet e-mail.
> Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
> or call Juno at (800) 654-JUNO [654-5866]
>
> --
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Dave:
<P>If you have the new AEA CIA-HF, you don't need to do ANY computation,
it is all done for you automatically using its R<FONT SIZE=-2>L</FONT>
measurement capability. I apologize, you do need to divide by two
and subtract a residual reading in your head.
<P>It also has an outomatic distance to first fault measurement that is
easy to use and interpret.
<P>73/Mike, N7ML
<BR>Mktg. Dir.
<BR>AEA div. Tempo Research Corp.
<P>k6ll@juno.com wrote:
<BLOCKQUOTE TYPE=CITE>This is a repost with a more relevant subject line.
Recent
<BR>discussions of feedline losses on a kt34 and recurring
<BR>threads reminded me of this oldie, which I first posted
<BR>about four years ago.
<P>A good thing to do every year or so is to measure your
<BR>feedline losses. If you have an antenna analyzer that reads
<BR>high values of swr with reasonable accuracy, the measurement
<BR>can be done from the comfort of your radio room, without
<BR>disconnecting the antenna.
<P>Attach the analyzer to the feedline in question, with the antenna
<BR>still connected. Tune the analyzer's frequency until you see the
<BR>highest peak in indicated swr on the meter. There will usually
<BR>be several high peaks. Pick the highest one near the high end of
<BR>the analyzer's range.
<P>Plug the peak observed swr into the following equation:
<P>LOSS = 10LOG((SWR+1)/(SWR-1))
<P>For example, if you see a peak swr of 8 at 24 mhz
<P>LOSS = 10LOG(9/7) = 1.09 dB at 24 MHz
<P>Then all you have to do is consult a coax loss chart to see if
<BR>the measured loss is reasonable for the type and length of
<BR>coax being used, and whether it would be cost effective to put up
<BR>new/different coax.
<P>The reason this method works is that almost all antennas present
<BR>a high value of impedance when operated outside their design
<BR>range. This high impedance is a close approximation of an open
<BR>circuit, and the equation above is valid. This idea was
<BR>presented in QST a few years ago, but the author presented a
<BR>graphical, rather than mathematical, solution. I like the mathematical
<BR>solution better, because you don't have to go back and dig up the QST
<BR>article to find the graph.
<P>Some people distrust the accuracy of high value swr readings
<BR>obtained on inexpensive analyzers, and prefer to take
<BR>repeated measurements over several years to detect trends,
<BR>rather than believing the absolute numbers. That's ok too.
<BR>Whenever I have used the above method to measure brand-new coax,
<BR>the results have always agreed closely with expected losses.
<P>Dave Hachadorian, K6LL
<BR>Yuma, AZ
<BR>K6LL@juno.com
<P>___________________________________________________________________
<BR>You don't need to buy Internet access to use free Internet e-mail.
<BR>Get completely free e-mail from Juno at <A
HREF="http://www.juno.com/getjuno.html";>http://www.juno.com/getjuno.html</A>
<BR>or call Juno at (800) 654-JUNO [654-5866]
<P>--
<BR>FAQ on
WWW:
<A
HREF="http://www.contesting.com/towertalkfaq.html";>http://www.contesting.com/towertalkfaq.html</A>
<BR>Submissions:
towertalk@contesting.com
<BR>Administrative requests: towertalk-REQUEST@contesting.com
<BR>Problems:
owner-towertalk@contesting.com
<BR>Search:
<A
HREF="http://www.contesting.com/km9p/search.htm";>http://www.contesting.com/km9p/search.htm</A></BLOCKQUOTE>
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FAQ on WWW: http://www.contesting.com/towertalkfaq.html
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