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Author Topic: RG8 for j-pole?  (Read 9819 times)

Posts: 12

« on: April 14, 2013, 03:45:34 AM »

I'm ordering the Arrow 2m/70cm J-pole and '25 feet of pre-asembled
coax to go with it. I believe RG8 is what I need. I just need some
confirmation before I order it.
Thanks, KK4MSE.

Posts: 6252

« Reply #1 on: April 14, 2013, 05:51:19 AM »

RG8 is a heavy cable, good for quite a few permanent installation types. It is hard to work with, though, not being very flexible.  To get around that, RG8X cable is used.  It is more flexible with just a bit more loss than RG8, but not as much as RG58.  You may even be able to get by (only 25 feet) with RG58, but its use on the UHF frequencies tends not to be as popular since the signal loss of RG58 is quite high at those frequencies.

For your j-pole and a 25 foot run, I would go with RG8X.  It's a compromise, but the signal loss difference between RG8 and RG8X is negligible, and you'll have a lot easier time using (running) the RG8X.

Posts: 17484

« Reply #2 on: April 14, 2013, 10:02:44 AM »

Just to avoid some confusion:

Hams have traditionally talked about "RG-8", but that military designator has been
discontinued and replaced by RG-213.  While there are reputable companies still
making "RG-8 type" cables, you can also find junk, as there is no longer an
enforceable standard for it.  There was also an RG-8A version, but most hams
ignored the last letter.  RG-213 (or a reputable RG-8 type) is a good choice for
low loss if you don't have to snake it around corners or in through a window.

RG-8X (or what Radio Shack called "RG-8M Minifoam") is a smaller diameter cable
(about the size of RG-59) that is a good compromise between flexibility and loss,
due to the foam dielectric.  (Authentic RG-213 has a solid polyethylene inner
insulation, though there are some "RG-8 type" foam cables around.)  Foam cables
have lower losses for the same diameter, but are more prone to damage due to
compression (being stepped on, tie wraps pulled too tight, sharp bends heating
up in the sun, etc.)  While losses are slightly higher than RG-213, it is easier to
route through holes in the wall or other tight spots where flexibility is useful.

One source of confusion of course, is the habit of ignoring the last letter, in which
case RG-8X becomes RG-8, which has a different diameter and uses different
connectors.  So generally I talk about RG-213 to avoid that confusion.

You can use VK1OD's handy transmission line loss calculator to compare cables:

For example, for 25' of matched coax on 445MHz, RG-8 or RG-213 is 1.3dB, or
about 1/4 of your power is lost in the coax.  Using RG-8x the loss is 1.8dB, so
1/3 of your power is lost.  If you are running 10 watts, that is the difference
between 7.5 watts and 6.7 watts, which you probably won't notice in practice.
With RG-58 (which is even thinner and more flexible) you lose 50%, so you'd
have 5 watts radiated.  In most cases, that probably won't be significant in
operation, either, and the mechanical properties of the cable may play a
bigger factor in your choice.

Sometimes the differences in losses ARE important, but if you a choosing a
J-pole and only need 25' of coax, they probably aren't.


Posts: 125


« Reply #3 on: April 14, 2013, 05:01:59 PM »


Check out the KB9VBR J-pole website. If you are going to get a j-pole,
I recommend Mike Martens copper j-poles, they work. Mike does quality
work at affordable prices. I'm not saying Arrow doesn't make a quality
product, but the copper ones work much better than the open stub Arrow.

For a 25' run, RG-8x will work fine.


on Facebook:

Posts: 12

« Reply #4 on: April 15, 2013, 03:21:11 AM »

What I'm looking at is Cable Experts 25' RG8U with PL-259s
at AES. The coax will run from the J-pole down then through
the garage wall, then down to the radio.

Posts: 3207


« Reply #5 on: April 15, 2013, 05:27:09 AM »

...... I'm not saying Arrow doesn't make a quality product, but the copper ones work much better than the open stub Arrow......

Can you point me to any test data that supports your claim?

Posts: 125


« Reply #6 on: April 15, 2013, 10:13:26 AM »

The short version is no, we didn't record or log signal strength readings in detail.

The longer version...One of the local hams purchased a 10 pack deal for the
discounted price of buying in bulk. Since we live in a hurricane prone area, a
majority of us tried them for use as an emergency backup, should we need
to take down our primary antennae systems. One ham, built his own copper
j-pole after trying the Arrow. We could quickly see the difference in base to
mobile coverage on simplex. While the 2m range was increased by about 25%
with the copper j-pole, the uhf coverage almost quadrupled. All of us replicated
the results after switching from the Arrow to the copper j-pole. At each location,
the Arrow was replaced with a cooper j-pole on the same mast, location, height
and using the same cable, with the same results.

So, even though we didn't plot coverage maps or take db per meter readings at
100' intervals, the results were quite apparent to those who participated. FWIW:
only one person has continued to use the j-pole on 2m/70cm in the group, while
everyone else went back to the Comet GP-9, Diamond X-510, Workman and Opek
UV-300's for regular use, which of course, far outperform the copper j-poles.

Again, this was on simplex, by a group that is on simplex on a daily basis, whether
base, mobile or portable. Repeater coverage would probably not be that noticeably
different between the two antenna, but we didn't focus on that aspect.     

Arrow does make a nicely machined product that is very durable.

Posts: 1555

« Reply #7 on: May 15, 2013, 09:29:56 AM »


Any chance we could talk you out of getting a J Pole, and instead getting a name brand vertical of some type (Diamond, Comet, etc).  They are much, much better designs, with coax decoupling and gain that are far better than a J Pole.

Some like J Poles due to simplicity and ruggedness, but have real issues with decoupling the feed line (eg. need coils of your RG-8 at the base), so why even mess with it unless you have a compelling need for a J Pole specifically?

Good luck.

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