[SECC] Coax replacement

Thu Nov 12 18:06:53 EST 2020

Cats will tend to catch critters even if they are well-fed. They just won’t eat them. I speak from experience….

Good info on the coax. My coax run to the A3S is 19 years old, and I replaced the rotator loop as part of my rebuild, but I haven’t yet decided to replace the run up the tower. It wasn’t as exposed as the rotator loop.

I’m adding a grounding block at the top of the tower, so I can replace the run to the shack at any time.

How do you go about measuring the loss of the coax? What’s the technique? 

> On Nov 12, 2020, at 9:38 AM, Jeff (W4DD) <w4dd09 at gmail.com> wrote:
> 
> OH no, Kevan hit on one of my hot topics, so I can’t resist adding to his info.
>  
> I too had read that coax should be replaced every 20 years.  I’ve had a 100ft piece of RG-213 in a black 4 inch drainage pipe to the tower for 20 years.  I test the loss every few years, but it actually has not gone up much, many half a dB at 28MHz.
>  
> What I have found is coax goes bad primarily because various varmints like to chew on it.  The biggest offenders, at least here north of Atlanta, are squirrels.  It seems they like chewing on it right down to the braid.  Once that happens, water infiltrates the braid and wicks along 10 to 30 ft.  The copper braid corrodes and the coax gets real stiff.  Losses seem to go up then.  The squirrels not only like coax, but also like rotor cables and control cables.
>  
> I’ve found two solutions:
> My wife has kinda adopted a feral cat (now spayed and living a good life).  That cat is she still is working some.  My wife says I owe her for the good job she did.
> Second solution, where critters are likely to chew on the cables (like near the base of the tower) I cover the coax with .5 inch split loom tubing.  You can get 100ft very
>  
> I went to the Orlando hamfest this year and did run across a hundred ft of almost new 50 ohm ½ inch Superflex (like corrugated hardline but more flexible).  The commercial vendor didn’t seem to want to haul it to another hamfest, so offered me both a 75ft piece and a 100ft piece for the price of a 75.  One of those deals that you are not looking for but can’t pass up.  I installed the 75ft piece to the tower base with a short flexible jumper at the house end and saw about a 1dB decrease in loss at 28MHz over the old coax.  In addition, it is a solid outside conductor so even it the critters chew through the jacket, no water will wick along the shield.  The other piece of Superflex may be used to feed a 6M beam one of these days, with an appropriate flexible jumper near the rotor.
>  
> My other project is to get a Tic Ring Rotor working and mount it on the tower at 50ft to turn the A-4 tribander.  That will allow me to rotate something for 15 and 20M.  but as Kevin said, we don’t move as fast as we used to.
>  
> And am working on several power line noise issues to the NE and SE.  I’ve identified the defective hardware on 5 of the 7 poles, and am awaiting the engineer and line crew.  Those noise sources killed me during the CQWW a few weeks ago.  Hard to hear weak EU through S-4 noise.
>  
> Jeff
>  
>  
> From: SECC <secc-bounces at contesting.com> On Behalf Of Kevan Nason
> Sent: Thursday, November 12, 2020 7:36 AM
> To: secc <secc at contesting.com>
> Subject: [SECC] Coax replacement
>  
> I like Jeff's, W4DD comment about posting at least once a month.
>  
> Here's something I put in another clubs newsletter about current activity at N4XL:
>  
> ·         Truth or fiction?  It came to my attention while preparing a presentation on different types of feedlines for our local club that most coax cables, including the non-contaminating type, have a finite lifetime of between 15 and 25 years. After that, the loss begins to creep up. I didn’t care enough when I first set up this station to record station data so have no idea what SWR or reflected loss changes have occurred over the years. It seems likely any changes due to aging coax would be waaayyy to slow for me to notice over the 20 years that have passed since I installed my coax runs; and to that point I can’t say I actually do have excessive loss. So, I started looking on the internet. Most posts say it should be replaced.  I ran across a discussion about this on the TowerTalk reflector (at least I think it was that one) where K3LR (I think) said he doesn’t replace his unless he sees a problem. He has quite a station so maybe it doesn’t need to be replaced.
>  
> 
> Looking at my exposed coax it is rough feeling and no longer shiny and black. For the most part, it is Davis Buryflex. I bought some new Buryflex for a doublet I installed a couple years ago. The 20-year-old cable seems to be more flexible than the new. Also, when I put the Rigexpert antenna analyzer on the 175 ft run out to the elevated vertical it says the 7 MHz return loss is a bit over 1 dB (one way) higher than the specifications say it should be. Since most coax runs were installed at the same time I assume they all would read similar loss.
> 
>  
> 
> It is getting harder to work as these bones get older. About 200 ft of my coax is
> 
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Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901