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!