HopeRF feedback

Werner Almesberger werner at openmoko.org
Tue Jun 22 19:33:14 EDT 2010

Ron K. Jeffries wrote:
> is using on-off keying [OOK] a very simple modulation

Hmm, given that the chips support GMSK, that choice would give
better spectrum efficiency. You could probably even sequeeze three
channels into the universal but very narrow 434 MHz ISM band :-)

> But using 816/915 MHz as the primary radio on a small general purpose
> computer will not provide the single
> most valuable new feature for Nanonote: Internet access
> without needing to tether to another computer.

Yeah, Metcalfe's law also reaches into these regions. When Wolfgang
mentioned the Slow-Fi idea to me, I suggested to make a Slow-Fi to
USB bridge (for a WiFi or Ethernet dongle), e.g., based on a
suitably simplified NanoNote design, so that at least connectivity
at one's premises wouldn't be a kludge.

> So for an add-on dongle, you need two models
>    Europe 868MHz
>    US 915 MHz

I wonder how a 868 MHz band circuit tuned to the 915 MHz band and
vice versa would perform, e.g., in terms of TX/RX attenuation,
spectral leakage, and parts of the circuit that are not supposed
to act as transmitters acting as one. If the effects aren't too
horrible, perhaps a ~891 MHz design could work im both worlds.

> WiFi has become ultra cheap and is a global standard.
> it is the practical solution, and by using the Atheros
> chipset open source drivers are available.

WiFi avoids all those headaches indeed. Having spent some time
trying to find solutions for bugs in Atheros' unfixable
closed-source firmware, I have some sympathy for attempting
something entirely different, though.

- Werner

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