Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Carbon fiber: RF insulator? Or conductor?  (Read 4171 times)
AC4RD
Member

Posts: 1235




Ignore
« on: April 05, 2011, 09:12:05 AM »

I've got a handful of 13-foot carbon fiber fishing rods.  It occurred to me the other day that one of them might make a support for a piece of wire used as a vertical antenna ...  several of them might make any number of other antenna projects.  They're remarkably light.   But is carbon fiber safe to have near elements that are radiating RF?  Is CF an insulator at RF frequencies?   Or will the CF soak up the radiated energy and get warm?   TIA! 
Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #1 on: April 05, 2011, 09:37:19 AM »

Is CF an insulator at RF frequencies? 

Carbon fiber itself?  No way.  It's a conductor, but a lossy one.

I would certainly treat carbon fiber poles as being fairly unsuitable for vertical antenna supports unless I actually tested them.  Tests aren't too hard though.

Hang a wire from a tree or something and see what changes when you bring the pole right up to it.  Most importantly, can you detect a reduction in the received signal?  You can probably do a pretty sensitive measurement within a couple of dB if you use a steady local signal source and measure the audio voltage somehow (record with a sound card, maybe even measure with a good AC voltmeter)

You can also check to see if the pole affects the impedance of the antenna.. a simple SWR measurement might tell you something, but with something like a 1/4 wave vertical over a good radial system and a lossy pole, the SWR could even get a little BETTER. 

A purely insulating pole will shift the frequency of lowest SWR down a bit.  A lossy pole will probably shift the best SWR frequency and change the SWR at that frequency, maybe for the better, maybe for the worse. 
Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
Member

Posts: 13335




Ignore
« Reply #2 on: April 05, 2011, 12:46:08 PM »

Remember that a carbon fiber rod isn't just made of carbon.  Just like fiberglass, the
strands are encased in epoxy resin.  That's why you'll probably measure a high resistance
if you check it with an ohmmeter.

If each strand runs the whole length of the fishing rod, then you could couple power to
it (especially if it is a multiple of 1/2 wavelength.)  If the fibers are shorter, they might
not be making contact due to the epoxy they are encased in, and it shouldn't be a problem.
Clearly the answer depends on the specific rods that you  are using, as two that look
identical may behave differently.

How would you test it?  A 13' rod should be resonant around 36 MHz.  I'd put it parallel and
closer to a dipole cut perhaps for 10m, or somewhere over 40 MHz, and check it with a dip
meter to see if I see two resonances.  If so you know it is conductive.

Or just use it as part of an antenna at high power and have a long QSO, then feel it and
see if it is warm.  If not, it isn't absorbing enough of your power to worry about.
Logged
AC4RD
Member

Posts: 1235




Ignore
« Reply #3 on: April 06, 2011, 04:22:30 AM »

Gentlemen, thank you for the input.   I think I'll give the rods to a friend who might actually use them for fishing, and stick with my wire antennas a bit longer.  :-)  Thanks! 
Logged
AJ3O
Member

Posts: 124




Ignore
« Reply #4 on: April 06, 2011, 10:29:31 AM »

If they are the stronger carbon fiber rods, just use them as a vertical support with home brew insulated stand-offs. It would make for a quick support for a wire dipole or use stand-offs and hang a wire vertically. That should work for you. No?
Logged
AC4RD
Member

Posts: 1235




Ignore
« Reply #5 on: April 07, 2011, 04:26:30 AM »

KB3VIM, thanks; I've got trees for antenna supports.  I just happened to see these rods on sale, online, and ordered four of them, without giving it much thought.  ("Without much thought" is how I do most things.)  I think I had vague ideas of putting up a couple of phased quarter-wave verticals for 15 meters on my roof, or something like that.   And it didn't occur to me to consider whether carbon fiber was appropriate or not.  :-/  Anyway, right now I need time to play with the radio more than I need any new antennas.  :-)
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!