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If you have a remote control car key, DON'T have that frequency. Otherwise, there seems to be little difference in practice. See http://openenergymonitor.org/emon/node/502

[n.b. It is MHz, not Mhz - Heinrich would be upset to know that you spelled his name with a lower case letter!]

Thanks Robert,

I thought i remembered an advantage of 868 to do with two communication?  something the kit might benifit from in the future? or have i got my wire(less)s communications crossed :)

must remember MHz not Mhz

must remember MHz not Mhz

must remember MHz not Mhz

must remember MHz not Mhz

I'm not sure what you mean by "two communication". The two frequencies have different rules about channel occupancy - the percentage of time that any one device is allowed to transmit - so that other users can get a look-in. In the UK the channel occupancy is limited to 10% at 433 MHz, 1% at 868 MHz.  Apart from that I don't think anyone has conclusively demonstrated that in practice one is better than the other given a particular set of conditions.

Jean-Claude Wippler (owner of JeeLabs and creator of the library that we use) wrote [http://forum.jeelabs.net/node/248.html]:

"Wireless range is not just sensitivities and power levels. In the house, you also need to take HF radio signal attenuation into account ... i.e. walls and cabling and other objects absorb and weaken RF signals. Generally speaking: the lower the frequency, the better it travels through all sorts of materials (including ourselves, BTW). And the lower the transmit rate is set (default is ≈ 50 kbit/s), the better the receiver is able to extract the right data from a weak signal, as several reports on this forum have indicated.

I wouldn't immediately go with these choices, though: in many cases, reception will be fine (and even with a stronger signal, you'll get occasional interference from RF noise sources). Another trade-off: lower freq's require (slightly) longer antennas.

Speaking of antennas: that's probably another choice which could have a huge impact on range, i.e. with directional antennas. I haven't tried that yet.

There's more: if you choose the 433 MHz band, but happen to have lots of devices in the neighborhood on that same frequency, then you can still end up with limited reception and lots of interference. We used to have a wireless headphone @ 433 MHz, which completely took down my entire 868 MHz network while turned on. I still haven't out why, but the interference was unmistakable."

But if you have a conductive mesh, the shorter the wavelength in relation to the mesh size, the easier it will penetrate.

Sorry should have been 'two way communication', i cant remember where i read it or what exactly it was linked to now, was some months ago when i first found openenergymonitor, was spending a lot of time reading a lot about different approaches to monitoring and automation,

The choice of frequency is quite independent of that. We only use two-way between the Base and the emonGLCD - the GLCD sends the inside temperature to the base, and the base sends the time to the GLCD. You can of course set up your own two-way link for other purposes if you want, but you can't realistically use battery power for the receiver if you do so, as the receiver must stay awake to be able to receive.