revisiting the 434 MHz band

Werner Almesberger werner at openmoko.org
Fri Jul 23 06:09:08 EDT 2010


Wolfgang Spraul wrote:
> Come on, don't hide behind me.

Heh, but it does help if you explain what you don't like about the
chips/modules others seem to have no trouble with. Some of the
reasons are not trivial (e.g., if the chip/module is hard to source
or if there's something that promises trouble down the road.)

> Then I said "NO! I will not send this to Werner.

Phew. Groundhog day narrowly averted :-) Thanks !

> I keep reading more about SiGe Semiconductor, www.sige.com. Can you check
> their ICs and modules a bit?
> For WLAN, it seems they have a number of products
> http://sige.com/products/wireless-lan/details.html

Hmm, all I see there are various RF amplifiers. Nothing about
modulation/demodulation, tuning, encoding and clock recovery,
etc.

The MAX2830 I mentioned earlier seems to have all of what SiGe have
and a lot more:
http://www.maxim-ic.com/datasheet/index.mvp/id/5367

Note that you still need to process the analog I/Q signals. I only
have a vague understanding of this, but I think this means two ADCs,
two DACs, and some signal processing. Here are some articles on I/Q
modulation:
http://education.tm.agilent.com/index.cgi?CONTENT_ID=4
http://zone.ni.com/devzone/cda/tut/p/id/4805
http://en.wikipedia.org/wiki/IQ_Modulation

I think the MAX2830 does roughly what one transceiver (TX+RX)
daughterboard in the USRP does. The SiGe chips would be something
like half a TX/RX board.

For comparison, the Sub-GHz chips and the IEEE 802.15.4 chips also
do full modulation/demodulation, clock recovery, frame start
detection, checksum, etc., sometimes even up to automated
handshaking. (The latter not only saves the host CPU some work, but
it also helps to meet tight timing requirements.)

That's by the way also why I'm not convinced that using a module
would help you much with these - the chips already integrate
almost everything you need.

- Werner




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