You are not able to measure the losses in a coax when you terminate it with a
matched load (such as a dummy). The 56 ohms you are reading is the total error
in the meter, the coax and the dummy load.
If you disconnect the dummy load and set the "259" in "loss" mode you are able
to measure the loss. If you set the 259 in "loss" mode and connect the dummy in
the other end you will get a very discouraging result as the meter will
indicate a very high loss in the cable.
A little warning: The MFJ-259B and all the other MFJ's SWR meters are very
useful instruments but are not any "Gold" standards. You always have to take
the results as an "indication" as the errors sometimes can be very large, 10 -
20 % are not unusual.
I use the MFJ-259B every time I set up antennas and if the adjustment withe
MFJ-259 looks good my transmitter usually likes it. ;-)
Best 73 and good luck with you loss measurement,
Hans - N2JFS
-----Original Message-----
From: Pete Smith N4ZR <n4zr@contesting.com>
To: TOWERTALK <TOWERTALK@contesting.com>
Sent: Fri, Apr 4, 2014 9:56 am
Subject: [TowerTalk] Elementary feedline loss question
If I terminate a long 50-ohm coaxial cable with a 50-ohm dummy load, and
put an MFJ-259B on the other end, and it reads R=56, X=0 at a given
frequency, what is the mathematical relationship between the measured R
(leaving calibration out of it, for now) and the loss in dB?
--
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
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