revisiting the 434 MHz band

Werner Almesberger werner at openmoko.org
Wed Jul 21 19:13:11 EDT 2010


I wrote:
> Wolfgang Spraul wrote:
>> 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.

Ah, I think I didn't quite answer your question.

Atmel's AT86RF212 example cicuit in figure 3-1 on page 10 of [1]
has a configuration where it uses the same balun/filter combination
for both bands (table 3-1). Note that this chip is for IEEE 802.15.4
and uses OQPSK, not the OOK/(G)ASK/(G)FSK in most other devices for
these bands.

Freescale's MC33696 isn't multi-band capable because its crystal
depends on the band.

Microchip MRF49XA and Silabs Si4421 (EZRadio, not EZRadioPRO !),
which are essentially the same chip, use the same external
components for 868 and 915 MHz, with the exception of a VDD bypass
capacitor. See see figure 4-1 on page 71 of

For the Si443x series (EZRadioPRO), Silabs specify some small
differences between 868 and 915 MHz in AN427 and AN435, but it's
hard to tell which ones are merly optimizations.

Semtech change the matching network quite a bit between 868 and
915 MHz for their SX1223, table 33 on page 21 of [3], and a bit less
for their SX1230, figures 18 and 19 on page 33 of [4]. Note however
that the latter is an optimization and they say one can also use the
circuit from figure 15 on page 31.

TI's CC1020 uses the same circuit for 868 MHz and 915 MHZ, see table
13 on page 19 of [5]. It's the same for the CC1150, table 14 on page
15 of [6]. I'm too lazy to look up the other two chips in the CC1xxx
family :-)

Regarding Analog Devices, first of all, there is an error in my
previous table. None of the AD701x should be there, because they're
only transmitters, not transceivers. Second, there are hints that
the reference boards seem to differ between 868 and 915 MHz, but
it's not quite clear to me why.

[1] http://atmel.com/dyn/resources/prod_documents/doc8168.pdf
[2] http://ww1.microchip.com/downloads/en/DeviceDoc/70590b.pdf
[3] http://www.semtech.com/images/datasheet/sx1223.pdf
[4] http://www.semtech.com/images/datasheet/sx1230.pdf
[5] http://focus.ti.com/lit/ds/symlink/cc1020.pdf
[6] http://focus.ti.com/lit/ds/symlink/cc1020.pdf

By I'm also not sure that going 868/915 MHz is such a good idea, but
because the 868 MHz band seems to be quite crippled compared to the
915 MHz band or the 2.4 GHz band.

- Werner




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