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433MHz vs. 868 MHz/915MHz ?

Added by sketchy over 5 years ago

jcw responded to this question:Which RF12B? SMD, SMD2 or DIP/433MHZ or 915MHZ (http://forum.jeelabs.net/node/248.html)
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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.
For what scenario would one choose the 433 MHz over the 868 MHz/915 MHz?
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So the reasons cited for one over the other:
1. lower frequency = more distance between JeeNodes and JeeLink
2. if there are alot of devices using a frequency, the frequency will be noisy. So use the other frequency.

What if you want to go to production and don’t know a home’s use of a frequecy = which frequency should be used?

Is there other factors? It seems for the most part folks would get the 433MHz models?

Thank you.


Replies (2)

RE: 433MHz vs. 868 MHz/915MHz ? - Added by martynj over 5 years ago

sketchy,

Tough question in the general case - the ISM bands are license-free, shared and not all vendors follow the rules/conventions. The band occupancy varies over time, perhaps invalidating a survey at a particular location.

So you fall back to the basic physics:

The strongest signal wins:

* good antennas count
* 433MHz is absorbed more passing through interior walls

Key is Signal/Noise ratio:

* Slower data rates decode better in higher noise levels
* Maybe another channel in the band is quieter

A rather fuzzy answer but too many YMMV factors to be more specific. The good news is that most “small” nets, with appropriate system design to cope with lost packets work just fine.

RE: 433MHz vs. 868 MHz/915MHz ? - Added by sketchy over 5 years ago

Thank you martynj . I wonder when I asked Shawn at Modern Device before purchasing that he recommended the 915MHz…From what you say and what I have researched I’d prefer the 433 MHz.

Your info was very useful.

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