Dear fellows,
We developed a network plan to communicate between two CR1000s datalogger. The system consists of two buoy stations containing a CR1000 and a RF401 radio modem w/ a 3dBi omni antenna (Buoy 04 and Buoy 10), and a server station at the pier which asks for data from the other stations through GetVariables() command via Pakbus protocol.
This server station has a CR1000 and a a RF401 radio modem w/ a 3dBi omni antenna either. The Buoy 04 is 2.77 miles away from the server station and the Buoy 10 is 0.75 miles distant from the pier.
We'd tested this network configuration at the lab, with the radios very close together and it worked. We were able to monitor variables from the buoy stations' CR1000s on the Public table running at the server station's CR1000.
However, when we'd installed the system at the site we didn't get any information from the further buoy and incomplete data from the nearest buoy.
We're suspecting it to be a range problem, as we have no problem of sight, but we don't know if is it the radio model or the antenna's capability? We've seen on the Campbell's website that the range increases with a directional (yagi) antenna, but we can't switch this because of the buoys' motion.
If the omni antenna at the pier could be replaced by two directional antennas pointing at each buoy, would it solve the communication problem?
The radios are configured as Pakbus Aware, < 2mA (1 sec) power mode and Low Retry Level. Is there any other system configuration that could be more effective?
Regards,
Francisco.
I am by no means an expert but I believe that radio wave propagation over a water surface can be inhibited due to rapid changes in humidity. I found a quote in the book, "Essentials of Radio Wave Propagation" that seems to back this up. Different frequencies can have an impact on this as well. Unfortunately, the RF401 has a fixed frequency.
There are a couple of things that you might try:
- Increase the retry level for both the base and the remote radios.
- Increase the height of the base radio antenna
One or both of these things might help depending on how marginal the signal is to begin with.
Hi Francisco,
0.75 miles (1.2km) should be good. I've achieved that over flat land. 2.77mi (4.5km) is too far in my experience (over flat land with very few trees.)
Hooking up two directional antennas to one radio would be a problem due to impedance mis-match, but maybe someone with the right knowledge could design an adapter that could do that? I've not heard of it being done before.