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I have a 40' section of RG-8 that is about 35 years old. One end was terminated with a standard PL-259 and the other was soldered directly to an antenna.

When I removed the connector from the one end, the cable itself appeared pristine. The other end needed a few inches removed but also appeared pristine when the obviously weathered part was removed.

Is there any reason not to reuse this cable? I'll be using it on a dual band, 2m/440 ground plane.

Edited to add: This cable has been indoors for most of its life.

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Yes.

Left alone in a warehouse, undisturbed, it probably degrades in some fashion, though any time I have ever seen a find like that there is usually a feeding frenzy as people take it in part or in whole for use. So I don't have any personal knowledge about that kind of degredation.

In your Q, you hit the nail on the head. Often the coax will be fine and the connectors are of the most concern, usually due to water intrusion.

But consider the effects of the elements to the coax, particularly sun exposure. Any coax exposed to the elements will definitely degrade over time due to heat cycling and perhaps mechanical wear.

Typically the outer cladding is likely to become brittle and thus be more likely to crack if you bend it. Then water intrusion will cause eventual degradation of the shield.

To the point of your question, RG-8 is pretty rugged, and if it is still working after 35 years I can't think of any reason not to repurpose it. I would definitely suggest cutting the ends and installing new connectors.

Particularly with THAT Antenna. When I saw the first pictures of it, the end that was soldered to the antenna was definitely weathered. My very first thought was that the antenna end needed to be reterminated. And weather sealed.

But I didn't notice any problems with the cable away from that end.

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  • $\begingroup$ Thanks for the good information. I've edited the question to mention that this cable has been indoors for most of its life. When in use, the antenna was mounted in an attic. $\endgroup$ – Lance Aug 16 '17 at 22:13
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    $\begingroup$ Non-contaminating coax does not have the plasticizers in the jacket, and lasts much longer. Whichever type you have, at 440 MHz we would do better with something like LMR-400. But since you have it, why not try it? $\endgroup$ – Mike Waters Aug 16 '17 at 22:40
  • $\begingroup$ Yes, I know LMR-400 would be a lot better but right now I have old RG-58. The RG-8 will probably be an improvement over that. I'm poor, so I can't afford the luxuries of things like cables that, if people, would be too young to drink. $\endgroup$ – Lance Aug 18 '17 at 1:10
  • $\begingroup$ There are multiple grades of RG-58 Like /U and such, that describe the dielectric and the shield. A lot of hams will twll you that if you want to use RG-58 that instead you should use RG-8 (which is what PL-259 connectors are designed for. But hey, if that's what you have on hand, by all means use it. BUT you probably will want new connectors. To use RG-58 or rg-59 in the PL-259 connectors, there are screw-in adapters to make it fit better, but I have gone without those and had things work fine. Just don't put too much solder down the center part ot you will short it out. $\endgroup$ – SDsolar Aug 18 '17 at 6:45
  • $\begingroup$ RG-8 and RG-58 are 50-ohm, and that is probably fine for your antenna. RG-11 and RG-59 are for 75 (really 72) ohms and are good for dipoles. If you have a 1:1 balun that would be good, for dipoles. But you don't need that for groundplane antennas. Anyway, all I would add is don't pump 100 watts into it until you know the connections are secure. And don't worry about specs and numbers. Just try it and see what results you get. Begin by receiving, of course. Most of all, have fun with the project. No matter what happens you will learn something. At schools that is expensive - valuable. $\endgroup$ – SDsolar Aug 18 '17 at 6:49
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With old coax the things you're most likely to see are UV degradation of the insulation and water ingress.

Visually inspect the insulation, looking for cracks when bent. If this cable was not exposed to the sun, it's probably fine in this regard.

Water ingress will show as corrosion on the conductors, an increase in loss, or a change in characteristic impedance. The ends are most susceptible, so remove them if the shield appears corroded. For the outdoor end you might consider removing a couple feet more to be safe. There may also be nicks or fine cracks in the insulation that allowed water to enter which you may not be able to see.

Put a dummy load on the far end of the cable, and check with an antenna analyzer. The SWR should be flat over the entire range of the analyzer. If you don't have an analyzer, a directional coupler in conjunction with a signal generator or low power transmitter works also.

To check for loss, you can make a simple RF detector to measure the peak voltage:

schematic

simulate this circuit – Schematic created using CircuitLab

Use a Schottky diode for best sensitivity, though an ordinary silicon diode like 1N4148 may work well enough. Keep the leads between the resistors, diode, and capacitor as short as possible. The voltmeter can have long leads since it's measuring DC. Ordinary 1/4W resistors are fine as long as testing is limited to low-ish powers (<10W) and brief (a couple seconds) periods.

I build it into a BNC connector. This one worked fine at 440 MHz:

enter image description here

Measure the power directly from your antenna analyzer / signal generator / low power transmitter. Then put it on the end of the coax, and measure that. Power is proportional to the square of voltage.

$$ \text{loss (dB)} = 20 \log_{10} \left(V_\text{in} \over V_\text{out}\right) $$

If the cable passes visual inspection, SWR test, and loss test, it's fine to be reused. And you'll also know the loss, so you can decide if it's worth getting some better coax.

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Cables come in different classes. I do not remember the details, but there is for example RG8/U, RG8A/U, RG8B/U, RG223 and probably more. All those are pretty equivalent, but some have a short life time because the cheap PVC outside the screen will migrate into the polyethylene dielectric and cause (severely) increased losses. Read here: http://www.smeter.net/daily-facts/4/fact29.php

A cable with a polyethylene jacket is safe for ageing, but less so for fire. I think you can find specifications for the lifetime of different cable types if you look carefully at manufacturer data.

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