On 5/29/2013 10:36 PM, Jim Brown wrote:
On 5/29/2013 9:32 AM, William Hein wrote:
I have some 1-5/8 inch Andrew Hardline (LDF7-50A) which has been
stored outside in New England for 5 years - is it still good and if
not can it be rehabilitated?
I'd say it depends on whether water has penetrated it, which in turn
depends on whether the ends were weatherproofed before that 5 years
began. It also depends, of course, on whether it might have taken
lightning hits.
I can thinl of two problem with water. If it gets inside the hollow
center conductor and freezes it could rupture the conductor, possibly
introducing a discontinuity which would probably be OK for our power
levels on HF, but it should be thoroughly dried out. OTOH it could be
quite a problem at UHF and up
The other is end penetration between the dielectric and shield and
between the dielectric. As the foam is closed cell it probably wouldn't
be a serious problem on HF although I think it could create a layer of
oxide. It's unlikely the water would penetrate more than a foot or two
, but not impossible. In most cases removing a foot or two off the end
should be sufficient and allow a visual check.
However Jim's suggestion of the VNA is a good one and an important check
of any old or unknown coax. It can give you loss at any frequency, a
profile of the coax for discontinuities within a foot or two, and a
check of the velocity factor when used as a TDR.
If you know the impedance and velocity factor it can tell you how much
is in a coil or left on a reel.
This is a great application for using a VNA (vector network analyzer) to
measure loss and do a TDR sweep (Time Delay Reflectrometry) to look for
damage. To do TDR, you'll need connectors on at least one end, and to do
loss, you'll need connectors on both ends.
It might take adapters, but some VNAs come with calibration resistors.
There are some very good ones
If you don't own a VNA, ask around your neighbors -- there's a good
chance that someone you know owns one and will volunteer to sweep it for
you.
VNAs like the AIM 4170 cover up through 2 meters and run just shy of 600
with all accessories including a nice protective carrying case.
If you really want UHF coverage it'll run close to a grand, but a great
idea for a club purchase.
I use the less expensive 4170C and not only check the antennas and feed
lines from the operating position, but by switching it to the tuner I
can tune far faster and to an SWR beloe 1.0X. Often to less than
1.00X:1 and see the return loss at the same time. Record the traces
from the VNA and TDR showing the antenna characteristics, write protect
the files and you can then call up the files and hit retrace which will
give you a display of the original characteristics withe current ones as
an overlay to instantly see any changer in the feed lines, switching,
and antennas.
The device is far more versatile than an SWR meter.
This becomes evident the first time you use a tuner and see what happens
to the return loss, or the 2:1 points in frequency.
I have a 3 position Alpha delta switch on the input to the tuner. One
position goes to the rig and the other goes to the VNA. I can tune the
amp into the dummy load and the antenna with the VNA, switch back to the
rig and it's ready to go.
73,
Roger (K8RI)
73, Jim K9YC
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