I'm planning a sensor network for agriculture (that apparently doesn't exist yet in this form) and I'd like to understand the possibilities of the radio link.
A good number of in-the-field soil sensors would collect 3-4 analog inputs once per hour and send these to a concentrator / gateway which forwards them to the Internet. Only one-way transmission is necessary as it's not critical when packets get lost every now and then (no ACK necessary).
It's important that the sensor modules are cheap and can run for years on batteries. Size and shape is not critical but I'd like to fit the electronics in a compact round housing of about 15cm diamer.
The concentrator on the other hand could be a bit bigger and run on battery-backed solar energy. Depending on the RF range it would handle something near 1000 sensors, maybe.
The 169 Mhz band (free to use at 500 mW ERP = +27 dBm in Europe) seems interesting, as I understand the relatively low frequency allows a wide reception range.
I could use any protocol, but wireless MBUS seems to be a good choice and after all 169 MHz band is meant for that.
- What RF range can I expect (rural area)?
- How critical is the antenna? Would it make sense to have a 1/4 wave helical antenna (14cm) on the sensor (or preferably something smaller) and combine it with a 48 cm omni antenna on the concentrator/gateway?
- How critical is the position of the sensor (TX) antenna (which would be more or less on the ground, while the concentrator (RX) could be on some 2 meter pole)?
I'm trying to understand the possibilities now and would then let do a professional company all the engineering.