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I am in charge of a temperature monitoring and controlling project in a new building with 7 floors and 14 rooms by floor.

I installed last week thermostats devices in each rooms permitting to send user set point temperature to a master device (2 by floors located in corridors) which are driven the underfloor heating.

The system works fine, but sometimes, I have some communications problems between thermostat and its master device due to the fact that the building is a bit too long for a good communication.

All communications between devices is done by RF 868MHz.

I am looking for ideas helping me to improve the RF communications between devices

HoneyWell Devices list :

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closed as off topic by Leon Heller, Dave Tweed, Brian Carlton, zebonaut, Kortuk Jan 19 '13 at 0:52

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    \$\begingroup\$ This sounds like a bad application of RF. These are long term fixed items, so run the wires. It will be more reliable. \$\endgroup\$ – Olin Lathrop Jan 18 '13 at 13:24
  • \$\begingroup\$ I agree that wiring the sensors up would be a far far better deployment. It sounds like you may have a capital equipment nightmare on your hands if you already purchased 14 * 7 = 98 wireless thermostats. \$\endgroup\$ – Michael Karas Jan 18 '13 at 15:57
  • \$\begingroup\$ I agree. Usually, we refurbish small buildings and RF devices are really interresting. But for this big building, use wire was most expensive but a better solution. FYI, 90% of the devices manage to communicate with their masters without problem, for the other 10%, the comm more difficult. \$\endgroup\$ – sdespont Jan 18 '13 at 16:32
  • \$\begingroup\$ Is there some repeater device I could use or others tricks to improve the communication between most devices spaced? \$\endgroup\$ – sdespont Jan 18 '13 at 16:32
  • \$\begingroup\$ @sdespont I will bet that if you contact those that sold you the product they have a solution for this already, like a repeater or a better antenna, probably a repeater though. This seems to be consumer electronics support that we can give design advice for RF, but if they have a repeater you will save yourself tons of money just buying a few. \$\endgroup\$ – Kortuk Jan 19 '13 at 0:54
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A repeater for that system would probably have to be protocol aware (ie made by Honeywell). A simple repeater arrangement that tried to receive at 868MHz and retransmit would introduce a slight phase delay. If the receiver is already receiving the original transmission most of the time that would likely confuse the data demodulator.

You could try pulling them apart and seeing if fitting a larger antenna to one end is possible. Depending on the original antenna something like a small 1/4 wavelength whip (around 8.5 centimeters at that frequency) may double the range. Improving the antenna increases both the transmit and receive gain, so just changing one end of the system may be enough and is worth trying.

Note that the various regulations on RF emissions are based on radiated power, so doing that may put it over the approved limits for license-free devices in your region.

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