Antenna ground plane and coax grounding

"Bill French" wrote in message
...
I have been having some transmission problems in my rag wing airplane -
not getting the transmission distance I should be getting.

On the way to the radio shop for a SWR check I could send and recieve at
2000' AGL for a distance of 40 miles behind me. Report of 5 square.

Returning over the same course I was at the same altitude but could only
get a 4 x4 at 30 miles.

SWR check showed between 2.5 and 2.9 - acceptable but just barely.

Changed antenna and had the same reading.

My ground plane is an aluminum plate about 12" by 8" and the antenna is
mounted at the extreme forward end - that is toward the cockpit.

This probably accounts for the differences in for and aft transmissions.

I've read that the ground plane or reinforcement plate that the antenna
is mounted should be grounded.

Is it sufficient to have it grounded through the coax shield and then
have the shield grounded to the airframe at the radio or should the
plate be grounded at the antenna?

Would I be better off trying to increase the size of this plate with
aluminum foil or something similar?

Any help greatly appreciated.

Bill French
The grounding should ideally be at both ends of the coax.
Make sure that it is a good solid ground to give the best results.
When grounded to the airframe, the airframe also becomes part of the ground
plane , so your signal will radiate best to the rear. if possible, try
moving the antenna toward the center of the fuselage.

"JLB" wrote in message ...


What frequency are you assuming? 22" is a quarter wavelength at 134 Mhz,
which is a bit too high for the aviation band.

Can you say velocity factor?

"JLB" wrote in message ...
Last time I checked the velocity factor of air is pretty close to
1.00000000.

Yeah, but the velocity factor of the material the ground counterpoise is being made out
of is the issue.