Another antenna question

[David Wilson]

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

[Orval Fairbairn]

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.

[Jim Weir]

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

[pete365]

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.
>
>

[Jim Weir]

Here's the theory...all antennas are "dipoles". You know, those rabbit ear
things we used to have on top of our TVs when we watched Eisenhower take the
oath of office. Di (two) pole (rod). Two rods. Remember the Frankenstein
(That's Franken SCHTIEN to you, bozo) movies where the Jacob's ladder started in
the middle and slowly progressed to the end, where it disappeared. Did it
really disappear? No, it transformed itself from one form of energy to radiated
energy. Don't believe me? Try and receive an AM radio station with one of
those suckers in the same room.

Now, it comes to pass that almost all of the energy that we put into the rods
where they come close at the center will be transformed to radiated energy when
the rods are an odd multiple of a half-wavelength long. The rods, being equal,
are therefore an odd multiple of a quarter-wavelength long each (with a finagle
factor shortening them up about 5% for such esoterics as velocity factor and end
effect). The shortest dipole is with the odd number 1 as the multiplier, which
is why we usually just say that the dipole ears are a quarter-wave long.

Just like we can trick somebody into thinking we are where we ain't with
mirrors, we can trick one of the dipole ears to think that it has the requisite
other ear by putting a metal "mirror" underneath it. That is, the dipole looks
into the mirror and "sees" what it thinks is the other dipole ear (really just
an image of itself) and is quite happy to radiate...IF the mirror is an odd
multiple of a quarter wave from rod to edge.

Fortunately for us, the mirror doesn't have to be one continuous sheet of
metal...it can be broken up into smaller sheets, rods, tubes, wires, and other
metalmongery. If it is the metal fuselage of a metal aircraft or the metal
framework of a tube'n'rag aircraft, the theory is that SOMEWHERE in that
conglomeration of metal, there will be SOMETHING that is an odd multiple of a
quarter-wave (about 22" at 127 MHz.).

That's the long answer. The short answer is that your mounting plate should be
electrically tied to the metal framework of the airplane at every opportunity...

Jim




Bill French >
shared these priceless pearls of wisdom:

->The antenna base plate on my ragwing ( Bellanca Decathlon) is
->approximately 12" long by 8" wide and sits on wooden formers on the
->turtle deck that are centered on the main longeron - Decathlon /
->Citabria triangular fuselage structure - and about 2" above it.
->
->The front and rear ends are flanged downward and there is a metal tab on
->the longeron at each end of the plate. The tabs are about 2" from the
->flange.
->
->Is it necessary to bond both ends of the plate to the fuselage tabs to
->use the steel frame as an adequate ground plane or is just bonding one
->end sufficient?
->
->I'm bonding the plate with a piece of aluminum the same width as the
->plate and then tapering to approximately 3/4" where it joins the tab.
->
->I'm concerned about setting up improper radio signals by having the
->plate just grounded at one end.
->
->Also crawling into the fuselage rear section when you're 5' 11" and 220
->lbs is a real pain so would just like to do this job just once.
->
->Any help greatly appreciated and thanks in advance.



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

[Jim Carriere]

Fitzair4 wrote:
> CELL PHONE ANTENNAS//??????
>
> Some of use have a office in our metal hangers. Using a cell phone is not
> always the best to Rec/Transmit.
> Anone know of what size and type of antennas to put on the roofs of our hangers
> for the Cell phones?
> A good article, for Jim to write for the "Aero Lectrics" Magazine information
> story.

Larry, look around in marine supply shops. Boaters sometimes use aux
antennas for cellphones, with and without boosters. I remember
reading this on one of the cellular newsgroups. Once you find what
you're looking for, I suppose you can find it cheaper on Ebay.

And, uh, did you mean "hangar?" :) Sorry, couldn't resist.

[Blueskies]

Seems pretty funny; hook a cell up to a wire so it will work...Any such thing as a wireless repeater for those babies?

--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html


..
"Jim Carriere" > wrote in message ...
> Fitzair4 wrote:
> > CELL PHONE ANTENNAS//??????
> >
> > Some of use have a office in our metal hangers. Using a cell phone is not
> > always the best to Rec/Transmit.
> > Anone know of what size and type of antennas to put on the roofs of our hangers
> > for the Cell phones?
> > A good article, for Jim to write for the "Aero Lectrics" Magazine information
> > story.
>
> Larry, look around in marine supply shops. Boaters sometimes use aux
> antennas for cellphones, with and without boosters. I remember
> reading this on one of the cellular newsgroups. Once you find what
> you're looking for, I suppose you can find it cheaper on Ebay.
>
> And, uh, did you mean "hangar?" :) Sorry, couldn't resist.
>

[Blueskies]

Thanks, Jim, for a short and sweet explanation!

--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html


..
"Jim Weir" > wrote in message ...
> Here's the theory...all antennas are "dipoles". You know, those rabbit ear
> things we used to have on top of our TVs when we watched Eisenhower take the
> oath of office. Di (two) pole (rod). Two rods. Remember the Frankenstein
> (That's Franken SCHTIEN to you, bozo) movies where the Jacob's ladder started in
> the middle and slowly progressed to the end, where it disappeared. Did it
> really disappear? No, it transformed itself from one form of energy to radiated
> energy. Don't believe me? Try and receive an AM radio station with one of
> those suckers in the same room.
>
> Now, it comes to pass that almost all of the energy that we put into the rods
> where they come close at the center will be transformed to radiated energy when
> the rods are an odd multiple of a half-wavelength long. The rods, being equal,
> are therefore an odd multiple of a quarter-wavelength long each (with a finagle
> factor shortening them up about 5% for such esoterics as velocity factor and end
> effect). The shortest dipole is with the odd number 1 as the multiplier, which
> is why we usually just say that the dipole ears are a quarter-wave long.
>
> Just like we can trick somebody into thinking we are where we ain't with
> mirrors, we can trick one of the dipole ears to think that it has the requisite
> other ear by putting a metal "mirror" underneath it. That is, the dipole looks
> into the mirror and "sees" what it thinks is the other dipole ear (really just
> an image of itself) and is quite happy to radiate...IF the mirror is an odd
> multiple of a quarter wave from rod to edge.
>
> Fortunately for us, the mirror doesn't have to be one continuous sheet of
> metal...it can be broken up into smaller sheets, rods, tubes, wires, and other
> metalmongery. If it is the metal fuselage of a metal aircraft or the metal
> framework of a tube'n'rag aircraft, the theory is that SOMEWHERE in that
> conglomeration of metal, there will be SOMETHING that is an odd multiple of a
> quarter-wave (about 22" at 127 MHz.).
>
> That's the long answer. The short answer is that your mounting plate should be
> electrically tied to the metal framework of the airplane at every opportunity...
>
> Jim
>
>
>
>
> Bill French >
> shared these priceless pearls of wisdom:
>
> ->The antenna base plate on my ragwing ( Bellanca Decathlon) is
> ->approximately 12" long by 8" wide and sits on wooden formers on the
> ->turtle deck that are centered on the main longeron - Decathlon /
> ->Citabria triangular fuselage structure - and about 2" above it.
> ->
> ->The front and rear ends are flanged downward and there is a metal tab on
> ->the longeron at each end of the plate. The tabs are about 2" from the
> ->flange.
> ->
> ->Is it necessary to bond both ends of the plate to the fuselage tabs to
> ->use the steel frame as an adequate ground plane or is just bonding one
> ->end sufficient?
> ->
> ->I'm bonding the plate with a piece of aluminum the same width as the
> ->plate and then tapering to approximately 3/4" where it joins the tab.
> ->
> ->I'm concerned about setting up improper radio signals by having the
> ->plate just grounded at one end.
> ->
> ->Also crawling into the fuselage rear section when you're 5' 11" and 220
> ->lbs is a real pain so would just like to do this job just once.
> ->
> ->Any help greatly appreciated and thanks in advance.
>
>
>
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com