I have made a board on which xbee is connected. it communicates with another xbee, 3meters away from it.


Now I have to seal the box. box is made of delrin. I have left small opening from where antenna can come outside. I have to sela the box, since weather is harsh, low as -10C.

I am using xbee with wire antenna:
http://www.digikey.com/product-detail/en/XB24-AWI-001/XB24-AWI-001-ND/935965



1. I will fill entire circuit with potting material to make it weather proof. My question is how much antenna height should I keep ouside the box.

 

for a plastic box, none. the way to test for absorption of rf in plastic or potting terial is to put some in a microwave, along with a half cup of water, and run it a while, if it heats up, it absorbs rf energy.

 

That plastic box is tied over long metallic pipe.

Other box, which is also plastic to which first box communicate with xbee, is also tied over metal pipe?

 

Monopole antennas (1/4 lambda or colinear) should be mounted orthogonal (not parallel) to a metallic ground plane. In this case, the ground foil on the pcb is likely parallel to the pipe, so the Monopole should stick up...

If you have two, I would make sure that the two antennas are in the same plane. Crosspolarization results in a 20db signal loss...