[VHFcontesting] Expected life of coax
k7wwa at saber.net
Tue Jun 28 01:12:29 EDT 2005
There are many things that will affect the usable life of coax so I will try
to answer the second part of your question since that will help you decide
when or if you need to replace it.
You need to measure and RECORD the loss in the cable when you install it or
if you did not do it then, do it now. You need to know the length of the
cable and need to consider the frequency of interest. If it is feeding an HF
antenna, there is no need to do your measurements at 500MHz. On the other
hand if it is used with your 1296 antenna, you need to perform the loss
measurements at 1296. You need to use a "good" wattmeter or if you can get
them, two wattmeter's. I prefer the Bird 43 with the proper elements. Use a
good dummy load instead of an antenna to remove any possible effect from the
antenna. Using the attenuation charts that are available for most types of
coax, determine what your cable loss should be for that length of cable.
Compare that number to the loss that you measured with the wattmeter's.
Don't be concerned if your measured loss and the chart loss differs by 5% or
so because most good wattmeter's are rated at +/- 5%.
Every year(you pick the time frame) repeat your measurements, be sure to use
about the same frequency. If you see the loss increasing there is something
going on. Age, water, physical damage to the cable. My advice is if you see
a 3db increase in the loss you might consider replacing the cable run but
only after you check the connectors. Only you can decide if it is worth the
cost to replace the cable or put up with the loss.
There are other measurement tools that can be used to measure cable loss. I
have used several of them but most of them cost a lot more than one or two
Bird 43 wattmeter's.
Just my $0.02
From: vhfcontesting-bounces at contesting.com
[mailto:vhfcontesting-bounces at contesting.com]On Behalf Of John Geiger
Sent: Monday, June 27, 2005 5:51 PM
To: vhf at w6yx.stanford.edu; wsvhf at mailman.qth.net;
vhfcontesting at contesting.com; dx-list at yahoogroups.com;
cq-contest at contesting.com
Subject: [VHFcontesting] Expected life of coax
What is the life expectancy of Coax (type 9913 superflex and RG-213) in a
high UV environment like Oklahoma? And how can I tell when it is time to
73s John NE0P
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