Another antenna question

In article ,
"David Wilson" wrote:

Still looking for an external antenna for my handheld. I am now thinking
about putting it on the back side of the baggage compartment inside of the
fuselage. This is in a wood and fabric airplane. The back of the
compartment is approximately 8"x24" made out of 1/8" plywood. What I would
like to do is use a piece of sheet aluminum (8"x24") on the back inside of
the baggage compartment for the ground plane and putting the comm antenna
inside the fuselage behind the baggage compartment. The antenna I would
need to use would be one with the 45 degree bend in it.
Is this a big enough ground plane? If not could I bend the sheet at 90
degrees and extend the aluminum out horizontally to get more area. Also
does
it matter if the antenna is in the middle of the ground plane.
Thanks
Dave




The ground plane should, at a minimum, extend in all dierections from
the base of the antenna, at least one antenna length. Yes, it does make
a difference if the antenna is not at the center of tthe ground plane --
it will alter your radiation pattern.

What Orval says is true, theoretically. The ground plane should extend in all
directions from the base of the antenna a quarter-wave. For the com band this
is about 22", and the antenna should be in the dead center of this sheet of
metal.

Having said that, an airplane is a bunch of compromises flying in loose
formation. If you can't get this size, or the antenna needs to be off-center,
then it won't be perfect. But it will "work", whatever that means.

Jim





Orval Fairbairn
shared these priceless pearls of wisdom:

-
-The ground plane should, at a minimum, extend in all dierections from
-the base of the antenna, at least one antenna length. Yes, it does make
-a difference if the antenna is not at the center of tthe ground plane --
-it will alter your radiation pattern.

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

I built my own. I used a piece of 1/8" brass welding rod about 17
inches. I soldered it to the center pin of a male BNC connector (radio
shack) I then ran a piece of small wire insulation over the joint to
insulate it from the outer shell, then potted the whole thing with
epoxy. I then drilled a hole through the center of an inspection plate
on the belly of the fuse( cherokee) and mounted a female BNC and ran
the cable into the cabin. For ground clearance I bent back the antenna
about 45 deg. Its been on the belly for over 10 years, and still
working. It has the advantage of quick disconnecting for washing or
other servicing. Its probably not perfect, but it works. For wood and
fabric, you could add an internal metal sheet, or just a couple of 22"
wires to the connection point. Remember, your portable radio doesn't
have much of a ground plane when held in your hand, but it seems to work ok.
Pete

Orval Fairbairn wrote:

In article ,
"David Wilson" wrote:



Still looking for an external antenna for my handheld. I am now thinking
about putting it on the back side of the baggage compartment inside of the
fuselage. This is in a wood and fabric airplane. The back of the
compartment is approximately 8"x24" made out of 1/8" plywood. What I would
like to do is use a piece of sheet aluminum (8"x24") on the back inside of
the baggage compartment for the ground plane and putting the comm antenna
inside the fuselage behind the baggage compartment. The antenna I would
need to use would be one with the 45 degree bend in it.
Is this a big enough ground plane? If not could I bend the sheet at 90
degrees and extend the aluminum out horizontally to get more area. Also
does
it matter if the antenna is in the middle of the ground plane.
Thanks
Dave






The ground plane should, at a minimum, extend in all dierections from
the base of the antenna, at least one antenna length. Yes, it does make
a difference if the antenna is not at the center of tthe ground plane --
it will alter your radiation pattern.