Groundplane for transponder

Anyone with depth knowledge of groundplanes for transponders?

- their mission (any theory would be appreciated)?
- required dimension
- required shape (is a cross OK or does it have to circular)
- material (is aluminium tape OK?)
- installation - follow the a/c body, or flat
- how critical is the above (loss of signal strength?)


regards


Jan Ivar

In article , "Mads"
wrote:

Anyone with depth knowledge of groundplanes for transponders?

- their mission (any theory would be appreciated)?

They complete the electronic circuit for the antenna.


- required dimension

1.5 feet from the center of the antenna should work fine. (1/4 wave)


- required shape (is a cross OK or does it have to circular)

Eight crossing strips of aluminum tape, about 3 feet long, should do
quite nicely.


- material (is aluminium tape OK?)

Yes -- as long as you have electrical contact with the antenna base.
Remove the adhesive at the center so that the aluminum tapes all contact
each other.


- installation - follow the a/c body, or flat


Doesn't matter too much.



- how critical is the above (loss of signal strength?)


Keep it away from other antennae.

A transponder antenna is only 2-3/4 inches long. That is a quarter wave
length at the transponder operating frequency. A disk as small 5-1/2 inches
in diameter will provide an adequate groundplane.

Wayne
http://www.soaridaho.com/Schreder

"Orval Fairbairn" wrote in message
news
In article , "Mads"
wrote:

Anyone with depth knowledge of groundplanes for transponders?

- their mission (any theory would be appreciated)?

They complete the electronic circuit for the antenna.


- required dimension

1.5 feet from the center of the antenna should work fine. (1/4 wave)


- required shape (is a cross OK or does it have to circular)

Eight crossing strips of aluminum tape, about 3 feet long, should do
quite nicely.


- material (is aluminium tape OK?)

Yes -- as long as you have electrical contact with the antenna base.
Remove the adhesive at the center so that the aluminum tapes all contact
each other.


- installation - follow the a/c body, or flat


Doesn't matter too much.



- how critical is the above (loss of signal strength?)


Keep it away from other antennae.

From: Orval Fairbairn


Keep it away from other antennae.


Just as a matter of curiosity is there a chart somewhere that lists minimum
distances between various types of antennae?

Dan, U.S. Air Force, retired

"Orval Fairbairn" wrote in message newsrfairbairn_spam_sucks-
1.5 feet from the center of the antenna should work fine. (1/4 wave)

A quarter wave is only on the order of a few inches for a transponder.

I'll throw in my 2 cents...
"Mads" wrote in message ...
Anyone with depth knowledge of groundplanes for transponders?

- their mission (any theory would be appreciated)?

To make an analogy, trying to use an antenna without a ground plane is
like trying to punch someone in the face whilst wearing ice skates.
Ya, just aren't going to get very much power out there because every
time you swing forward, your body moves back.

- required dimension

Larger in radius than the wavelength you are working with.

- required shape (is a cross OK or does it have to circular)

Round or bigger (ya know what I mean?)

- material (is aluminium tape OK?)

Large difference in dielectric constant from the medium you are trying
to transmit into. Aluminium is great. My worry with tape is that the
adhesive will act as an insulator bewteen layers. The tape I'm
familiar with would seem to fatigue if its on anything that could flex
and might give an intermittant behaviour if it did. If you have to
use tape, maybe use copper tape and run a bead of solder along there
edge wherever one strip crosses the other.

- installation - follow the a/c body, or flat

Flat is best, but many parts of a metal airplane look flat at 1GHz.
Signal propogation at these frequencies is line of sight (much more so
than your VHF nav/com radio) so position the antenna such that it has
the fewest obstructions back to the surveillance radar.

- how critical is the above (loss of signal strength?)

The difference between a good and bad antenna installation can be
easily 6dB. You payed a lot of money for your 200W transmitter, don't
throw that power away on a bad antenna installation.

Regards!

Thanks for the responce.

Do you know of any good websites with more indepth info on this?

Regards

Jan Ivar


"Jay" wrote in message
om...
I'll throw in my 2 cents...
"Mads" wrote in message
...
Anyone with depth knowledge of groundplanes for transponders?

- their mission (any theory would be appreciated)?

To make an analogy, trying to use an antenna without a ground plane is
like trying to punch someone in the face whilst wearing ice skates.
Ya, just aren't going to get very much power out there because every
time you swing forward, your body moves back.

- required dimension

Larger in radius than the wavelength you are working with.

- required shape (is a cross OK or does it have to circular)

Round or bigger (ya know what I mean?)

- material (is aluminium tape OK?)

Large difference in dielectric constant from the medium you are trying
to transmit into. Aluminium is great. My worry with tape is that the
adhesive will act as an insulator bewteen layers. The tape I'm
familiar with would seem to fatigue if its on anything that could flex
and might give an intermittant behaviour if it did. If you have to
use tape, maybe use copper tape and run a bead of solder along there
edge wherever one strip crosses the other.

- installation - follow the a/c body, or flat

Flat is best, but many parts of a metal airplane look flat at 1GHz.
Signal propogation at these frequencies is line of sight (much more so
than your VHF nav/com radio) so position the antenna such that it has
the fewest obstructions back to the surveillance radar.

- how critical is the above (loss of signal strength?)

The difference between a good and bad antenna installation can be
easily 6dB. You payed a lot of money for your 200W transmitter, don't
throw that power away on a bad antenna installation.

Regards!

Earlier, (Jay) wrote:

- required dimension

Larger in radius than the wavelength you are working with.

As Wayne Paul pointed out, for a quarter-wave whip like a typical
transponder antenna, a quarter-wave radius ground plane is really all
you need. A full wavelength would be around 22" in diameter. That's
way overkill for one of those little antennas.

My actual experience seems to validate that a 5.5" dia round or square
ground plane is adequate.

Thanks, and best regards to all

Bob K.

On Thu, 05 Feb 2004 10:14:59 -0800, Jay wrote:


To make an analogy, trying to use an antenna without a ground plane is
like trying to punch someone in the face whilst wearing ice skates. Ya,
just aren't going to get very much power out there because every time you
swing forward, your body moves back.

I can tell you watched much hockey.
--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Is that why they all carry those sticks?
;)
Peter