I have just read an article regarding an AR Op using a carbon fibre fishing
rod to make a 12 foot mobile antenna for mobiling.

My question is, does carbon fibre absorb RF?

The operator has wound 5.2 metres (approx 17 feet) of insulated house wiring
in a helical fashion around the rod. He uses an SG-237 tuner as well.

If indeed that carbon fibre is conductive, and he claims he is getting
outstanding results whilst operating stationery mobile, then what is
happening?

I would appreciate comments.
73.
John
VK2KC

Put some in a microwave oven and see if it gets warm.
Don't tell the wife!

Cheers

Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm

"VK2KC" wrote in message
...
I have just read an article regarding an AR Op using a carbon fibre fishing
rod to make a 12 foot mobile antenna for mobiling.

My question is, does carbon fibre absorb RF?

The operator has wound 5.2 metres (approx 17 feet) of insulated house
wiring in a helical fashion around the rod. He uses an SG-237 tuner as
well.

If indeed that carbon fibre is conductive, and he claims he is getting
outstanding results whilst operating stationery mobile, then what is
happening?

I would appreciate comments.
73.
John
VK2KC

On Mon, 07 Jun 2010 07:44:17 GMT, "VK2KC" wrote:

I have just read an article regarding an AR Op using a carbon fibre fishing
rod to make a 12 foot mobile antenna for mobiling.

My question is, does carbon fibre absorb RF?

The operator has wound 5.2 metres (approx 17 feet) of insulated house wiring
in a helical fashion around the rod. He uses an SG-237 tuner as well.

If indeed that carbon fibre is conductive, and he claims he is getting
outstanding results whilst operating stationery mobile, then what is
happening?

I would appreciate comments.
73.
John
VK2KC

My experience with Radio Controlled Model Airplanes has led me to the
conclusion that Carbon Fiber and its relationship to RF is
unpredictable.
John Ferrell W8CCW

If indeed that carbon fibre is conductive, and he claims he is getting
outstanding results whilst operating stationery mobile, then what is
happening?

I would appreciate comments.
73.
John
VK2KC

I can tell you my experience with an about 7.5-meter carbon-fibre fishing rod,
that I was intending to use as support for a 10-MHz vertical (the rod was
secured to an insulated support, with some radials lying on the ground).

What is did is to run a bare copper wire along the rod, fixing it to the rod
every 30cm or so using scotch tape. So, the antenna was the wire, and the rod
was just a support.

After tuning the wire for perfect resonance at 10.1 MHz, I applied 1kW RF power
to the antenna. The result was that the rod (and the tape) got quickly burned at
most of the points where the wire was fixed to the rod (the high-voltage
points).

It can be easily concluded that:

- the carbon-fire rod is indeed conductive
- its resistance is however too high for plainly using it as a radiator
(i.e.without the copper wire)
- even though running low power one would probably not experience the problems I
had, the antenna loss (in dB) caused to the fairly high rod resistivity would
anyway be significant, independently of whether one runs low or high power.

73

Tony I0JX
Rome, Italy

I'm told that composite carbon materials have quite different
conductivities in different directions, like a laminated transformer
core. At least this should minimize eddy currents.

Roy Lewallen, W7EL

"Roy Lewallen" ha scritto nel messaggio
...
I'm told that composite carbon materials have quite different conductivities
in different directions, like a laminated transformer core. At least this
should minimize eddy currents.

Roy Lewallen, W7EL

It looks like the rod I have used was built by winding a narrow tape on a
tapered cylindrical support (in spiral fashion).

73

Tony I0JX

Hi John

As I remember too if you use plastic conduit (in VK) the orange stuff
has no carbon but the grey stuff does. ie it has carbon mixed in when it
is extruded.

I don't know how good that info is, it's comes from way back in
anecdotal land. I just assume grey stuff is not to be used for radio
antenna system!

Not directly on topic but may be related.

Cheers Bob VK2YQA

VK2KC wrote:

My question is, does carbon fibre absorb RF?

"Bob Bob" wrote in message
...
Hi John

As I remember too if you use plastic conduit (in VK) the orange stuff
has no carbon but the grey stuff does. ie it has carbon mixed in when it
is extruded.

I don't know how good that info is, it's comes from way back in
anecdotal land. I just assume grey stuff is not to be used for radio
antenna system!

I have heard the same thing, but have used the grey conduit for antenna
construction in the past. I noted that a 2mtr band slim jim (J pole variant)
antenna had the same low SWR with and with out being inside a length of 32mm
grey conduit. I would assume some affect on the SWR if there was any
interaction.

--
Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm

Bob,
Have just wound a coil on 4" grey UPVC, but before I did I whacked it into
the microwave, and it certainly didn't show any signs of warming.
Maybe they have removed the carbon?

73
John
VK2KC
"Bob Bob" wrote in message
...
Hi John

As I remember too if you use plastic conduit (in VK) the orange stuff
has no carbon but the grey stuff does. ie it has carbon mixed in when it
is extruded.

I don't know how good that info is, it's comes from way back in
anecdotal land. I just assume grey stuff is not to be used for radio
antenna system!

Not directly on topic but may be related.

Cheers Bob VK2YQA

VK2KC wrote:

My question is, does carbon fibre absorb RF?

VK2KC wrote:
Bob,
Have just wound a coil on 4" grey UPVC, but before I did I whacked it into
the microwave, and it certainly didn't show any signs of warming.
Maybe they have removed the carbon?



basically, RF loss is not a controlled parameter for manufacturing.
Sometimes it might be fine, other times not.

The Tesla Coil builders use lots of PVC pipe as coil forms (as well as
things like cardboard concrete forms: Sonotube(r)) and there is huge
variability in dielectric strength. I would imagine that RF loss also
varies substantially.

If you're really obsessing, the loss varies quite strongly with
humidity. PVC readily takes up and releases moisture from the atmosphere.