Mark what kind of antennas are you using? If tape was the coax
           connected in the center. I assume they and the coax are
   bonded in
           so there is little you can do about changing anything having
   to do
           with that.

           The other thing I am curious about is the new box that converts
           the fuel sensor value to a variable frequency pulse. Please look
       inside
           and tell me the numbers on the chips if they are readable of
   course.
           Some manufacturers mask the numbers sometimes so it makes it
           more difficult to copy the circuit.

           The diodes Aubrey mentions may be embedded in the chip or
   chips what
           ever the case may be. In that case the only thing I think
   you can
           do is put them in a shielded box and move it away from the coax.

           --
           Paul Lamar ...No rotor no motor.


       Paul (and others),
       I made a breakthrough this  weekend on the fuel probe problem.  I
       rewired the right probe with shielded wire from the probe all
   the way to
       the EFIS.  Power up the EFIS and Nav/Com, hit PTT, and the gauge is
       steady as a rock.  The left gauge (the one that I haven't
   changed) still
       acted up as always, but it will be next to fix.  But the right
   one with
       shielded wire appears to be working great.  It was too late in
   the day
       to fly it, but I feel 99% certain that this has corrected the
   problem.

       Thanks to everyone that shared their ideas and suggestions on
   how to fix
       this very annoying (and potentially dangerous) problem.

       Mark S.
       25.5 hrs

       Congratulations Mark. You had a real bear of a problem there for
   awhile.
       These kinds of problems usually require real expensive instruments
       to trouble shoot like field strength meters and VSWR meters.

       Probably a good plan of attack is shield everything in an airplane
       including all the engine computer wiring.
       --
       Paul Lamar ...No rotor no motor.

   Paul,

   I have heard of others having this same type of problem with capacitive
   fuel gauges.  You would think the manufacturer would provide some
   guidance/assistance on how to correct this problem.  Oh well, such is
   EXPERIMENTAL aviation.  Thanks for your help.

   Mark

   They mostly deal with metal airplanes and they provide a better ground
   and some shielding. Also RG400 is the correct coax for metal airplanes
   with quarter wave antennas.

   I am still curious about your antenna. Did you use a tape antenna?
   Send me private email if you want to keep it on the QT :)

   Here are a couple of shots from that SA mag composite plane antenna
   article.
   I think you can just barely see where the coax is connected to the
   half wave antenna in the detail photo.

   BTW I notice that Cessna bought Columbia so you and Tom Parkes now
   own Cessna's :)
   I also notice Cessna opened a plant in China for LSA aircraft.
   --
   Paul Lamar ...No rotor no motor.


Mark's using a Bob Archer - he said so in a message I received on 2/14:


"Matt,

I can be heard very well, or so I'm told.  My nav/com is an SL-30 with a
Bob Archer antenna in the tail.  It was tested by a ham prior to
installation and checked out very well (don't remember the numbers).
Coax is RG-400 and is one piece from the antenna all the way up to the
radio.  The fuel gauges are the only thing that seem to be affected by
the radio.

Mark"


Regards,

Matt-

Sorry! That got lost in my mind :)

http://home.hiwaay.net/~sbuc/journal/bob_archer.htm

Sounds like they are for metal airplanes only with composite wing and
rudder tips. Any RF on the outside of the coax would be shielded by
the metal wings or vertical tail. I'll cc this to Bob.

I suspect the VSWR and the radiation pattern are different
if installed in a totally composite airplane.