Dave Platt wrote:
In article ,
Highland Ham wrote:

My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the
best performance ,although I doubt that it will be measurable.

My recollection is that the basic difference between the various
grades is the thickness of the copper walls. The thicker-walled pipe
is what's preferred for outdoor/buried use and/or higher pressures
(e.g. use on the supply side of a house's water-pressure regulator).

RF current flows only through the skin of a conductor... it doesn't
penetrate very far into the body. One web calculator I found says
that the skin depth of a 144 MHz signal in copper is around 200
micro-inches, or 1/5000 of an inch. If the tubing wall is
much thicker than this, the additional thickness will have no
significant benefit in reducing resistive losses.

Since even the thinnest-walled (Schedule M) copper pipe has a wall
thickness which is about a hundred times more than the skin depth,
there's no electrical benefit to using thicker-walled tubing (Schedule
K or L).

Unless there's some mechanical reason to want to use the heavier-
schedule tubing, I'd just stick with Schedule M - it's lighter, less
expensive, and should be plenty stiff and strong for most
applications.


----------------

Go the cheapest way, as recommended above. You can't tell the difference
between the various grades without laboratory grade measuring equipment.
Surely no one receiving your signal could ever tell the difference.

Ed, NM2K

OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?

Thanks for all your advice and help.

Tom Corker wrote:
OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?

Thanks for all your advice and help.



-------------


To me, no, it isn't worth the difference in price, nor the hassle in
handling the thicker coax. Were I working weak signal modes, it might be
a different matter, but then I would use hardline or 9913 at the minimum.

Ed, NM2K

Tom Corker wrote:
Is the RG213 worth the difference on VHF?

Only you can answer that question. For 12 meters on a
flat line on 2m, RG213 has ~1dB loss and RG8x has
~1.5dB of loss. (LMR400 has ~0.6dB of loss.) Is
double the price worth 0.5dB to you?

http://www.vk1od.net/tl/tllc.php
--
73, Cecil http://www.w5dxp.com

"Tom Corker" wrote in message
oups.com...
OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?


Tom,

On VHF FM, a dB or two of signal will affect a marginal contact. In your
situation, however, the better cable provides only slightly more than half a
dB of signal, hardly worth the extra expense.

I used http://www.ocarc.ca/coax.htm for that comparison.

Other comparison tables and charts are widely available on the Internet with
a search for "Coaxial Cable" Loss. The sample table below will line up
nicely in a monospace font, like Courier.

Coax Cable Type Signal Loss per 100 ft
Loss* RG-174 RG-58 RG-8X RG-213 RG-6 RG-11 RF-9914 RF-9913
1MHz 1.9dB 0.4dB 0.5dB 0.2dB 0.2dB 0.2dB 0.3dB 0.2dB
10MHz 3.3dB 1.4dB 1.0dB 0.6dB 0.6dB 0.4dB 0.5dB 0.4dB
50MHz 6.6dB 3.3dB 2.5dB 1.6dB 1.4dB 1.0dB 1.1dB 0.9dB
100MHz 8.9dB 4.9dB 3.6dB 2.2dB 2.0dB 1.6dB 1.5dB 1.4dB
200MHz 11.9dB 7.3dB 5.4dB 3.3dB 2.8dB 2.3dB 2.0dB 1.8dB
400MHz 17.3dB 11.2dB 7.9dB 4.8dB 4.3dB 3.5dB 2.9dB 2.6dB
700MHz 26.0dB 16.9dB 11.0dB 6.6dB 5.6dB 4.7dB 3.8dB 3.6dB
900MHz 27.9dB 20.1dB 12.6dB 7.7dB 6.0dB 5.4dB 4.9dB 4.2dB
1GHz 32.0dB 21.5dB 13.5dB 8.3dB 6.1dB 5.6dB 5.3dB 4.5dB
Imped 50ohm 50ohm 50ohm 50ohm 75ohm 75ohm 50ohm 50ohm