revisiting the 434 MHz band

Werner Almesberger werner at openmoko.org
Tue Jul 20 19:14:38 EDT 2010


When reading about the 434 MHz band, I often saw remarks suggesting
that it was regionally limited, much like the 868 MHz and 915 MHz
bands are. Yet, the Wikipedia article on ISM bands [1] doesn't
mention any constraints.

As it turns out, the 434 MHz band may be even more troublesome than
the 868 and 915 MHz bands. First of all, the German Wikipedia
article [2] indicates that the 434 MHz band is regionally
constrained. The article on short-range devices [3] adds more
constraints, like a maximum transmit power of only 10 mW. For
comparison, FCC 47.15.247 allows up to 1 W in the 2.4 GHz band [4,
5]. The article also claims that the 434 MHz band is full of
interferences and will face more restrictions in the future.

Furthermore, the 434 MHz band is notably absent in FCC 47.18.301
[6]. (The same text confusingly states on the next page that ISM
equipment is free to put as much energy in the air as it desires
[7], seemingly directly contradicting 47.15.257.)

[1] http://en.wikipedia.org/wiki/ISM_band
[2] http://de.wikipedia.org/wiki/ISM-Band
[3] http://de.wikipedia.org/wiki/Short_Range_Devices
[4] http://www.wi-fiplanet.com/tutorials/article.php/1428941/EIRP-Limitations-for-80211-WLANs.htm
[5] http://edocket.access.gpo.gov/cfr_2005/octqtr/pdf/47cfr15.247.pdf
[6] http://edocket.access.gpo.gov/cfr_2007/octqtr/pdf/47cfr18.301.pdf
[7] http://edocket.access.gpo.gov/cfr_2007/octqtr/pdf/47cfr18.305.pdf

This leaves two choices: 1) either live with a design that operates
in different bands, depending on location, or go to what appears to
be the only globally safe place, the 2.4 GHz band.

Regarding 1), it should be possible to meet regulatory requirements
for 868 MHz and 915 MHz with the same hardware, i.e., without the
need for regionally different hardware. Users would still have to
know whatever band(s) is/are available in their region, and
configure their system accordingly. Well, if you add a GPS
receiver, even this could be automated ;-)

- Werner




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