antenna ground planes

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I just bought a fiberglass homebuilt project with a conventional com
antenna mounted inside the leading edge of the vertical stab but it
doesn't have a ground plane yet. The instructions call for a 24in by
24in ground plane but there isn't that much room right there at the
base of the tail. Any suggestions as to what would work well? I
imagine there is info out there somewhere but am not sure where to
start looking.

many thanks,
steve

[COLIN LAMB]

If you have the room, make a vertical dipole. The bottom of the ground
plane will replace the horizontal surface. For the bottom, use a 24"
aluminum pipe. Connect the shield to the bottom pipe and run the coax down
the center of the pipe. It is better if the coax is centered.

That is all you need to do. Total length will be 48" plus the spacing of
the center insulator.

Colin

[Philippe Vessaire]

COLIN LAMB wrote:

> If you have the room, make a vertical dipole. The bottom of the ground
> plane will replace the horizontal surface. For the bottom, use a 24"
> aluminum pipe. Connect the shield to the bottom pipe and run the coax
> down the center of the pipe. It is better if the coax is centered.

> That is all you need to do. Total length will be 48" plus the spacing of
> the center insulator.
In my Minicab i don't have the place for a full straight dipole. I just
bend the lower wire and all fit inside the fuselage.

I works fine with a Becker radio.


By
--
Pub: http://www.slowfood.fr/france
Philippe Vessaire ҿӬ

[Bill Daniels]

> wrote in message
ups.com...
> I just bought a fiberglass homebuilt project with a conventional com
> antenna mounted inside the leading edge of the vertical stab but it
> doesn't have a ground plane yet. The instructions call for a 24in by
> 24in ground plane but there isn't that much room right there at the
> base of the tail. Any suggestions as to what would work well? I
> imagine there is info out there somewhere but am not sure where to
> start looking.
>
> many thanks,
> steve
>

Take a look at the flexible dipole antennas here:
http://www.wingsandwheels.com/page14.htm

Composite sailplanes have the same problem of no ground planes and
restricted space.

Bill Daniels

[RST Engineering]

> wrote in message
ups.com...
>I just bought a fiberglass homebuilt project with a conventional com
> antenna

What is a "conventional com antenna"?



mounted inside the leading edge of the vertical stab but it
> doesn't have a ground plane yet.

If it is installed in the leading edge of the vertical stabilizer, how do
you intend to get a 24" length of conductor forward out into the slipstream?



The instructions call for a 24in by
> 24in ground plane but there isn't that much room right there at the
> base of the tail. Any suggestions as to what would work well?

Until you answer the above two questions, I can't offer suggestions.

Jim

[Stealth Pilot]

On Wed, 2 Nov 2005 08:59:35 -0800, "RST Engineering"
> wrote:

>
> wrote in message
ups.com...
>>I just bought a fiberglass homebuilt project with a conventional com
>> antenna
>
>What is a "conventional com antenna"?
>
>
>
>mounted inside the leading edge of the vertical stab but it
>> doesn't have a ground plane yet.
>
>If it is installed in the leading edge of the vertical stabilizer, how do
>you intend to get a 24" length of conductor forward out into the slipstream?
>
>
>
> The instructions call for a 24in by
>> 24in ground plane but there isn't that much room right there at the
>> base of the tail. Any suggestions as to what would work well?
>
>Until you answer the above two questions, I can't offer suggestions.
>
>Jim
>
read it again jim.

inside the leading edge of the vertical stab ...like up inside it.
probably radio transparent fibreglass construction

how do you build a groundplane inside of the tailcone below it?

seems a reasonable post to me.
Stealth Pilot

[RST Engineering]

I *did* read it again. A "conventional com antenna" could mean anything
from a store-bought white fiberglass whip to a store-bought dipole to a
store-bought damn near anything.

And how FAR up the leading edge of the vertical stabilizer? Base right at
the fuselage junction? Six inches up? A foot up?

I understand radio transparent fiberglass. I don't understand the
configuration, and to simply spout "supposes" isn't a real good way to get
decent performance.

Jim



> read it again jim.
>
> inside the leading edge of the vertical stab ...like up inside it.
> probably radio transparent fibreglass construction
>
> how do you build a groundplane inside of the tailcone below it?

[abripl]

> A "conventional com antenna" could mean anything ...

Come on Jim. Most of us understood it to mean a regular 1/4 wave that
is used for metal airplanes with their "ground plane". You are
technically too correct sometimes.

There are all sorts of conventions addapted from coloqua. For example
"conventionaly" you know who Americans are. But America is a continent
and not a country.

[raptor]

On Thu, 3 Nov 2005 08:27:50 -0800, "RST Engineering"
> wrote:

>I *did* read it again. A "conventional com antenna" could mean anything
>from a store-bought white fiberglass whip to a store-bought dipole to a
>store-bought damn near anything.
>
>And how FAR up the leading edge of the vertical stabilizer? Base right at
>the fuselage junction? Six inches up? A foot up?
>
>I understand radio transparent fiberglass. I don't understand the
>configuration, and to simply spout "supposes" isn't a real good way to get
>decent performance.
>
>Jim

I wonder about something else. How long would a "full wave" antenna
have to be for aviation comm radios? I've got some old walkie talkies
that have those very long pull out antenna's, they must be 5 or 6
feet. Are those full wave? And do full wave antenna's get the best
possible reception? Of course, in an airplane, the space limitation is
the problem. I use a di-pole in the vertical stab of my Glasair.
If you use a 1/4 wave antenna, and since it's 1/4 the size of the
radio wave, does that mean you will only get 1/4 of the strength that
is available in a certain location?

[COLIN LAMB]

A full wave antenna wound not be what you normally want. A 1/4 wave antenna
gives you a good omnidirectional pattern, with limited nulls off the end.
If you installed a full wave vertical ground plane on an aircraft, it would
have a bit of gain - up.

Remember that gain is not free. It is realized taking the energy from one
direction and increasing it in another. Which direction are you going to
take it from? Easy when you are at a fixed location. Not so easy when you
are flying around in an aircraft.

What you hope to accomplish in a good installation is th make sure all the
connectors are installed properly, the coax is good and the antenna is tuned
for the proper frequency.

Regarding the ground plane, sometimes you have to do the best you can. If
there is not enough vertical room for a dipole or a ground plane, you could
install a 24" wire vertically in the vertical tail and then install a single
24" wire in the horizontal axis, also in the vertical tail. That will not
be perfect, but sometimes you have to live with less. You could also have
one vertical wire and three horizontal wires, serving as the ground plane,
with one in the vertical tail and two in the horizontal tail.

Colin

[RST Engineering]

"abripl" > wrote in message
oups.com...
>> A "conventional com antenna" could mean anything ...
>
> Come on Jim. Most of us understood it to mean a regular 1/4 wave that
> is used for metal airplanes with their "ground plane". You are
> technically too correct sometimes.

"Come on" my ass. I answer these questions on a daily basis and you have
absolutely no idea what sorts of permutations and combinations can arise ...
and what people mean by "regular" and "normal" and what it means to give
wrong advice. I like to think that when I answer a question it is because
I've got a pretty good handle on the situation and can give something that
is technically and structurally defensible. If you want to hipshoot
answers, then hipshoot the results. So far I haven't given any bad advice
when I've been given the whole scenario. That's 35 years of antenna advice.
For free, you will note, and I'll be damned if I will give advice without
knowing for sure the parameters.

>
> There are all sorts of conventions addapted from coloqua. For example
> "conventionaly" you know who Americans are. But America is a continent
> and not a country.

First of all, that is "colloquia" (sp), which is not a word but a
*******ization (not an "addapted" misspelling either) of "colloquial" which
IS a word. America is not a continent, not even "conventionaly" which is
also spelled wrong. North America is a continent. South America is a
continent. Evidently you've never had to teach or make up exams where
people have to be correct to get the right answer.

Jim

[Rob Turk]

"raptor" > wrote in message
...
>
> I wonder about something else. How long would a "full wave" antenna
> have to be for aviation comm radios? I've got some old walkie talkies
> that have those very long pull out antenna's, they must be 5 or 6
> feet. Are those full wave?

The lenght of the antenna is proportional to the frequency used. Your
'walkie talkies' are most likely 27MHz CB type. A full wavelength would be
11 metres, which is a bit long to handle ;-)

On your plane, the comm frequencies are from 118MHz to 136MHz. The
wavelength in the middle of that range is about 2.35 metre. You can probably
hide a full wave antenna for that frequency in a fuselage but there's other
considerations like impedance and radiation pattern that influence the
decision. I'm sure Jim will be able to tell you the nitty gritty details, I
would have to look it up..

Rob

[RST Engineering]

118 to 137. Full wave antenna isn't going to buy you squat. Quarter wave
is about as good as it gets.

Jim



"Rob Turk" > wrote in message
news:cCDaf.416$zc1.177@amstwist00...
> "raptor" > wrote in message
> ...
>
> On your plane, the comm frequencies are from 118MHz to 136MHz.