From: rbono@necis.UUCP ( NM1D)
Newsgroups: rec.models.rc
Subject: Re: Carbon fibre and radio interferance
Date: 31 Aug 92 16:55:39 GMT
Organization: NEC Technologies, Inc., Boxborough, MA

In article <BUDD.92Aug28095613@drynix.dfrf.nasa.gov>, budd@elxsi.dfrf.nasa.gov (Gerry Budd) wrote:
> In article <steveg-240892093900@52.10.18.134.in-addr.arpa> steveg@resntl.bhp.com.au (steve garlick) writes:
> 
>    I've just finished a mould for producing glider fuselages. I'm planning
>    to use carbon fibre tows to reinforce critical areas on the fuse. I want
>    to run tows down either side of the fuse and some from the base of the
>    fin and up. Does anyone have experience with RF problems with an aerial
>    inside such a fuse. (Note, I dont plan to completely cover with CF, just
>    2 strips down either side for vertical stiffening).
> 
> I've got carbon fiber tow laminated into the interior sidewall of my
> Conquest 120 pattern plane.  I run the receiver antennae and three
> long servo extensions the full length of the fuselage.  I've been
> doing this for years with no problems.  However, I fly JR radios.  I
> know some people who will not do this with their 1024 Futaba's.  They
> have had some problems with their receivers and don't want to take any
> chances.
> 

  I don't know if this makes sense to me?  Is carbon fiber conductive in
anyway? Can it shield or absorb RF energy?  I don't know. I wouldn't think 
so except that there are electronic devices made of some sort of carbon.  

 There are "carbon composition resistors", is this the same type of carbon
that is used to make carbon fiber? Generally, carbon composition (or carbon
film) resistors can be used in an RF circuits because they will not react to
the RF energy in a way that impeads the RF part of the signal (so to speak).
They will only represent pure resistance (no reactance).   If the carbon
fiber that we use has similar properties, then this may mean that carbon fiber
is partially conductive but shouldn't shield RF energy (I am not sure about
this).

 There could be one way to find out.  Many ham's (amateur radio operators) use
the following test to determine if a certain material will absorb RF energy.
NOTE: There is a bit of controversy over this, but most think it makes sense.

  Place some amount of the material in question into a microwave oven.  "Cook"
the material for one to five minutes (start with one minute at low power,
if it passes this test, go gradually up to five minutes at high power).
If the material DOES NOT HEAT UP, then it should be transparent to RF energy.
Microwave ovens work by subjecting their contents to 2.6 GHz high power (600
watts or so) of RF energy.  If a material doesn't heat up under this, then
there is a good chance that it will not absorb lower frequency or lower power
RF energy.

Be warned that some microwave ovens don't like to be run empty.  In this case
you can place a cup of water in the oven.  Just be sure that your test material
is not near the cup of water so that it is not heated by the steam or heat
that is generated in the cup of water.

 Additionally, one could use an Ohm meter to try and determine if the carbon
fiber will conduct any electricity.  It may read in the MegOhm range.  This
could depend on the length and/or thickness of the carbon fiber (and whether
the measurement was taken across the thickness or across the length of the
carbon fiber).

 If someone has some carbon fiber and tries this test, please let us know.

 Of course the SAFEST thing to do (in ANY case) would be to have the receiver
antenna exit the fuse immediately after the receiver away from any other
wires, and run outside the fuse away from all surfaces.
 
-- 
 /**************************************************************************\
 * Rich Bono (NM1D)              IMRICH              rbono@necis.ma.nec.com * 
 * (508) 635-6300                                       nm1d@nm1d.nh.usa.na * 
 \**************************************************************************/
Newsgroups: rec.models.rc