I am attempting to connect some underground sensors with 2.4ghz XBEE wireless. They are only about 10 feet (3m) apart and 6 inches(15mm) under the surface. These things can go several miles line-of-sight but I wonder what the propagation will be like through the earth. Any wisdom? Thanks

 

I have not tried to cut through dirt with 2.4ghz. I do know 2.4ghz will not cut through water. Water absorbs energy at 2.5g. For many years I got my internet over 2.4ghz from the nearest town. It did not work in the rain, or fog, or on high humidity days. It works well in snow. I don't know if that helps you.

 

I am attempting to connect some underground sensors with 2.4ghz XBEE wireless. They are only about 10 feet (3m) apart and 6 inches(15mm) under the surface. These things can go several miles line-of-sight but I wonder what the propagation will be like through the earth. Any wisdom? Thanks

Don't expect it to work well, but the only way to know is to try it and see. Be sure to recognize that one trial won't tell you that much (well, if it doesn't work, that may tell you all you need). Soil conditions change significantly over time, particular in response to temperature and moisture (the latter likely being the real issue for you, particularly at that frequency), so you need to test over as wide a range of conditions as you can expect to see.

 

There is a 900mhz XBEE that might work better.

 

There is a 900mhz XBEE that might work better.

Thanks for the idea. Yes, I think lower frequency is better and I forgot about the 900mhz stuff.

 

Don't expect it to work well, but the only way to know is to try it and see. Be sure to recognize that one trial won't tell you that much (well, if it doesn't work, that may tell you all you need). Soil conditions change significantly over time, particular in response to temperature and moisture (the latter likely being the real issue for you, particularly at that frequency), so you need to test over as wide a range of conditions as you can expect to see.

This is such a great reply and spot-on. Thanks for killing my project! I have had spectacular success with XBEE and miserable failure too. It can stop working for no apparent reason after you convinced the boss you were a genius. I am aborting this after several weeks of work but I wont paddle up that creek again. It was great while it lasted. I definitely owe you one!

 

My suggestion is to not expect it to work at all.
Lower audio frequencies have a better chance. Unless the ground is wet.

I am adding a note suggesting caution!!!
This is totally serious!!!
HIGH POWER UHF radiation can do a great deal of damage to living entities. That includes 2.4ghz RF at a power level to pass thru the ground. Read about "ground penetrating radar" and the power levels used.