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Author Topic: RG8U vs RG213  (Read 14389 times)
KC5AOS
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Posts: 54




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« on: December 16, 2010, 01:49:10 PM »

Research shows RG-8U has less loss.  But, some comments were found about RG-213 being quieter (whatever that means).

What do you guys think is the best for an HF installation?
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WB2WIK
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« Reply #1 on: December 16, 2010, 03:40:49 PM »

Research shows RG-8U has less loss.  But, some comments were found about RG-213 being quieter (whatever that means).

What do you guys think is the best for an HF installation?

I don't know what research you've been looking at, but this is nonsense.

RG8/U and RG8A/U by definition are very long obsolete and no longer in production nor available from anyone.  RG213/U is still current, and is the direct replacement for RG8A/U, but to a newer slash sheet of the military specification MIL-C-17.

A lot of "hobbyist" cables sold to hams, CBers, the commercial 2-way market, etc. are sold as RG8 "types" but aren't RG8/U.  RG8X "mini-8" is a .240" O.D. "type," which really is nothing at all like RG8/U ever was.  8214, 9913, LMR400, 9086, 9096, 9913F7, LMR400UF and a zillion other lower-loss .405" O.D. cables are "RG8 types" simply because they are .0405" diameter (like RG8 or RG213) and are 50 Ohms nominal impedance.  Other than those two similarities, none of them are anything like RG8/U, either. Smiley

If you want "mil spec" type stuff of this diameter, RG213/U or RG214/U are the current products.  For "commercial/hobbyist" cables there are lower loss stuff, none of which is as rugged as RG213/U, but is perfectly suitable for our use.  The lower-loss cables have air cell or "foam" dielectrics and fatter center conductors than RG8/U ever had, and as a result have lower loss, but they're still the same O.D.

Don't know what "quiet" means, but most of the low loss cables are double shielded, so they might have less radiation leakage than single shielded cables.  It would take a very unique environment to notice that difference.
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N3OX
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« Reply #2 on: December 16, 2010, 07:05:05 PM »

Don't know what "quiet" means

One thing it means is that you should never seek technical advice, even for the simplest stuff, from people who made those comments.

Here's one I found:

http://www.livecbradio.com/coax-cable.htm

It's absolute nonsense.  It's like people who think they can hear the difference between brands of speaker cables, but when put to a real test, they can't tell the difference between a fancy $40 cable and coat hangers.

http://consumerist.com/2008/03/do-coat-hangers-sound-as-good-monster-cables.html

===============

Frankly and honestly, if someone tells you something is "quiet"  and can't explain it differently they're blowing smoke up your a**.  They don't really know what they're talking about and they're just making stuff up.    It's not a technical term at all and if they're trying to make a real technical point, they'll have a back up explanation.  Someone who says "this coax is quieter" really should be saying "this coax is better shielded and picks up less noise if routed past a very strong RF noise source."  Someone who says an antenna or a radio is "quieter" should really be able to point to better signal to noise ratio or something else more objective.  Otherwise, at best, they're telling you about their feelings, and who knows if you'll feel all warm and fuzzy about reception using the same device? 

For 90% of ham radio uses, there's not going to be a noticeable difference on reception between the most poorly shielded junk cable and the best shielded cable out there (which is probably rigid outer conductor hardline).  Loss is an important issue.  Sometimes poor cable isn't actually the impedance it says it is (I had some "50 ohm" coax that was 60 ohms once).  But "quieter?"  No way.

There are a couple of things that might happen in ham radio where cable leakage, etc, was a problem, but you'd have to be building a really big contest station or a repeater to run into those.

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KC5AOS
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Posts: 54




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« Reply #3 on: December 16, 2010, 07:47:38 PM »

Alright, alright, 213 it is.  Gees, being out of the hobby for ten years I have really gotten rusty.  Thanks for the advice, I think I' just chuck the spool of RG8U I have had for years (it's kind of stiff any way) and purchase some 213.
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K7UNZ
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« Reply #4 on: December 17, 2010, 07:57:21 AM »

While I agree RG-213/mil spec is great (I have a load of the stuff in my garage), there is no good reason to dump what you already have on hand.  Use it!

Being stiff doesn't really mean anything, RG-213 is the same after sitting a while.  Just stretch it out in the sunshine and it will soften-up for easy handling.  RG-213 is the same in that regard.

To me, the big advantage to RG-213 has always been that it's direct burial stuff with a tuff hide.  Here in Arizona I just throw it on the ground, run it thru the scrub, and it seems to last forever.  I do usually change it out every 10 years, or so, just 'cos I have so much on hand (hi).

Anyway, waste not-want not, eh?

73, Jim/k7unz
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N3OX
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« Reply #5 on: December 17, 2010, 08:16:11 AM »

I never throw out cable without testing it first unless it has cracks and stuff.  A lot of it will stay good for a very long time.

A wattmeter and dummy load will show you if there's a serious problem.  RG-8 style (including RG-213) mostly has about 1db loss per 100ft at 28MHz.  You can measure at the radio and at the dummy load and calculate dB = 10*log(Pdummy/Pradio). 

You should get about 80W out the dummy load end of 100 feet of RG-8 style coax with 100W applied on the 10m band.  Whether or not you can detect small problems with your coax this way depends on how accurate your power meter is, and many aren't super accurate.

But chances are most meters agree with *themselves* pretty well up near the top end of the scale... and that's all that really matters for checking the loss of a line that doesn't have a ton of loss.  I've made a habit of checking brand new cable just as a reference point for testing later on.  I use an old Bird thruline section with a slug that's probably seen better days.  But measuring with it (or really any wattmeter I've ever tried) tends to agree very well with the published specifications for the cables.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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