revisiting the 434 MHz band

Werner Almesberger werner at openmoko.org
Wed Jul 21 12:20:19 EDT 2010


Wolfgang Spraul wrote:
> If you read long and contradictory regulating paperwork long enough,
> you will always find a reason not to do something.

True enough. It's always good to consider what happens if you don't
comply with the rules. Besides the obvious issues with getting
caught operating a radio device that interferes with other things,
you as a manufacturer also have the problem that you need to get
FCC and CE certification for your product.

> Am I reading the Wikipedia article correctly in saying that "ISM rules
> prohibit using ISM for communications"?

IANAL ;-) I would expect that this would limit your ability to
commercially operate, say, an alternative mobile phone network.

Maybe you'll find this one useful:
http://www-s.ti.com/sc/techlit/swra048.pdf

> Why have we started to look at the 433 MHz band in the first place? Because
> we find readily available and cheap RF ICs working in that band.

Interestingly, many of the places where I see the 434 MHz band
mentioned refer specifically to China. E.g., here
http://standards.ieee.org/getieee802/download/802.15.4c-2009.pdf

> Your
> suggestion of building hardware that can operate in both 868 and 915 is
> interesting, although I would feel better, technically and legally, if we
> wouldn't be the first ones doing such a design.

Far from it :-) One problem is that 868 MHz, while ISM, is still
heavily fragmented in Europe. On the other hand, 915 MHz in the
Americas seems to be quite friendly. I'm not sure if 434 MHz is
available in the US:
http://edocket.access.gpo.gov/cfr_2009/octqtr/pdf/47cfr15.240.pdf

There seems to be a 315 MHz ISM-like band in the US, but I haven't
found any more specific information about it so far.

One thing to consider is also that some bands have duty cycle
restrictions. So you could use them for remote controls or for
occasionally reading a few bytes from some sensors, but not, say,
for downloading a file.

> Do you know RF ICs or modules that can do this?

Here's an overview of some transceiver chips:

434 868 915
-----------
	x	Analog Devices ADF7010
    x		ADF7022
x		ADF7020-1
x   x		ADF7011
x   x	x	ADF7012, ADF7021, ADF7021-N, ADF7025
    x	x	Atmel AT86RF212 (IEEE 802.15.4)
x   x	x	Freescale MC33696
x		Maxim MAX7030, MAX7031, MAX7032 (MAX2510, MAX2511)
    x	x	Microchip MRF89XA
x   x	x	MRF49XA
x   x	x	Semtech SX1223, SX1230
	x	Silicon Labs Si4430
x   x	x	Si4420, Si4421, Si4431, Si4432
x   x	x	Texas Instruments CC1020, CC1070, CC1110, CC1150
		(plus the TRF590x/TRF690x series, which is EOL)

> In parallel, nothing against 2.4 GHz, let's see whether we can find an RF IC
> that meets our needs in that band. Any leads?

At least Atmel, Freescale, and TI all have IEEE 802.15.4/ZigBee
products in the 2.4 GHz band.

Oh, and if you want to build your own SDR WiFi, here's a starting
point:
http://www.maxim-ic.com/datasheet/index.mvp/id/5367

- Werner




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