Beware of Old Coax!

Don’t mess with old, untested coaxial cables! Really, it just isn’t worth the risk. It might seem like a good idea when you need another cable, but there are hidden gremlins in old coax as I recently discovered.

Corroded, blackened braid on old coax

I have a box full of old coax cables. Some of them don’t have a connector on one end, or no connectors at all. Before I use any of them I always test them first. Here is how I do it:

First step is a visual inspection to look for obvious signs of damage. If the outer insulation is cracked water may have gotten into the cable and caused corrosion. If everything looks good I connect one end of the cable to the dummy load in my MFJ-949E manual tuner. The other end is connected to my transceiver.

It is always to a safe idea to start with low power, maybe 10 watts, just in case the coax is faulty. After winding the power down I key up the radio in CW mode. Any mode that uses a carrier will work, for example, AM, FM – but not SSB.

We are looking for 1:1 SWR. If all is well at 10 watts, I crank the power up to 100 watts and key up again. If all looks good the cable may be okay, but you still can’t be sure. I tested one cable recently that had an intermittent fault. I narrowed it down to a bad connection between the cable and the PL-259 plug on one end. A good suggestion is to wiggle the ends of the cable while testing to check for things like that.

What to do with old cables that fail the dummy load test? I dispose of most of them. Some I keep so I can strip the braid to use as a ground strap or for some other purpose. Even the inner conductor can be re-used for hook-up wire. So, if you are a recycling advocate or (like me) a penny-pinching cheapskate you don’t have to send old coax to the landfill and can save money by storing scrap wire for re-use.

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