[TowerTalk] Marine Grade Coax -- NOT!

Tue Sep 26 00:03:26 EDT 2017

I think "marine grade coax" is another specialty, or niche market that 
has a percentage of cheap knock offs like the so called "digital" TV 
antennas for which I'm seeing a new round of advertisements. The audio 
industry with super high price wire and tubes for the unknowing was 
another place for cheap stuff at high prices.

There is junk coax advertised to us too, so when a knock off shows up, I 
wait for others to try it out.  Not all that inexpensive coax is junk, 
some of it has proven to be as good as the original and some hasn't.  I 
suspect the marine environment is much the same.

The words, "marine and aviation" carry with them the insinuation that 
those cables are every bit as good as the high priced spread, but there 
is no guarantee that they are as good as the real thing.  If it's really 
good enough for a certified airplane, it WILL be expensive.  When we 
purchase a new name coax it rarely comes with a warranty that it meets 
the demands of the marine, or aviation industry.

Quite some years ago (over 30) some of the local hams made connections 
that allowed them to purchase coax at substantially reduced priced.  
Some of the first was of outstanding quality. It was a quasi air core, 
similar to what we think of as the old 9913.   OTOH a batch of the most 
flexible RG-8 size cable I've ever seen came through. It would put 
today's LMR-400UF to shame. It had substantial braid coverage too, but 
it had an odor I didn't like. Since when did coax have an odor?  Color? 
IIRC It was a light gray.

I purchased enough to use for rotator loops on my 3 rowers at the time 
with enough extra for a planned 4th. IOW, not very much. Those loops 
were up through a summer back in the 70s... Hmmm...That's a lot more 
than 30 years, it's closer to 50.  At any rate, I noticed a buildup on 
the rotator loop while on one of the towers and that odor was strong 
from several feet away.  I decided to replace those loops. The buildup 
looked like disgusting scabs and the cable was sticky. That was the end 
of cheap coax.

73, Roger (K8RI)

On 9/24/2017 Sunday 4:58 PM, Jim Brown wrote:
> Several years ago, I did a friend a favor by providing guidance about 
> suppressing RFI to the HF installation on her sailboat. As you might 
> guess, I gave her a bunch of ferrite cores. In appreciation, she gave 
> me a short length (turned out to be 28 ft) of a so-called "Marine 
> Grade" coax with an Ankor brand. It had laid on a shelf outside the 
> shack until I picked it up a few days ago, put a connector on one end, 
> hooked it up to my VNWA, did a TDR sweep, made 5 MHz to 100 MHz 
> shorted and open impedance sweeps, and fed them to ZPlots to compute 
> Zo, VF, and attenuation.
>
> Results were unimpressive, but unsurprising given a physical 
> examination of the cable. It's labeled RG213, has a flimsy outer 
> jacket that is easily nicked, a tinned copper braid that's also easily 
> nicked, and what appears to be a stranded copper-clad steel center! 
> Loss was 0.77dB/100 ft at 10 MHz, VF was 0.669. The outer jacket came 
> to me nicked in one place (a slice about 0.5 in long), and there was 
> obvious staining from corrosion of shield that lay beneath it.
>
> The Ankor website describes their RG213 as having a "premium tinned 
> copper center conductor as well as a tinned copper outer braid for 
> corrosion resistance and easy soldering. It features signal loss 
> ratios of up to 50 percent less than other coaxial cables. 96 percent 
> braid provides best signal strength and least interference with UV 
> inhibited white jacket for longest life." The website contains no specs.
>
> In fact, loss is significantly greater than ordinary good quality RG8 
> and RG213 from companies like Belden, Times, and Davis RF, and 
> physical properties are significantly worse. Amazon sells a 100 ft 
> length for $95. And they'll sell you Shakespeare-branded gold 
> PL259-knockoffs for $12.87 EACH!  A gold plated barrel (also a 
> knock-off) will set you back $11.74. Compare with great coax like 
> Buryflex with AWG 9.5 stranded copper shield, foil plus tinned copper 
> braid shield, and really nice UV-resistant PE jacket. 100 ft costs you 
> $0.89/ft.
>
> This marine stuff is on the level of the ultra-expensive but useless 
> stuff sold to high-futility folks!
>
> 73, Jim K9YC
>
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-- 

73

Roger (K8RI)

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