Hello everyone,
This is my first post here and I really don't know if this is the right place to ask this but...
I am developing a project where we need to track mining equipment in underground mine shafts. The problem is GPS obviously doesn't work underground so our solution is to use small stationary transmitters embedded in the walls of the shafts and with each trackeble piece of equipment carring a receiver we record the time and ID of a transmitter. The transmitters have to be cheap and very low power as we are planning to make them disposable. The receivers are usually mounted on trucks and such and don't need to be very efficient. We considered RFID but that could become very expensive if every piece of equipment would need a several thousand Euro standalone RFID reader. So we went with low powered active beacons and receivers. Well all is well when testing in the office - we get ample range (upto some 100m in open space) and reliable detection but when we take the equipment outdoors in the rain or snow we get problems. We tried 2.4 GHz and it was very cheap and efficient, but we had trouble when the receiver or transmitter were near the ground or a big mass like a truck. Snow and moisture had very little effect on range. Next we tried RFM12B modules at 868 MHz that were unbelievably cheap but also performed well below levels advertised in datasheets. We could get the range but power usage was unacceptable because of low transmission speed and high packet loss. Now we have new modules and are just about to begin testing them but as these are 868 MHz again I have my doubts.
I would like to know if anyone has any experience with anything like this and any helpful pointers would be greatly appreciated. Especially any insight into what does and underground environment do to different frequencies and is this even feasible.
