[MLB-WIRELESS] 900Mhz

[Daniel Carosone]

On Sun, Oct 30, 2011 at 12:36, David Nuttall <david at smithsgully.net> wrote:

>  Hi Dan,
>
> The US 900 MHz license free band goes from 902 to 928 MHz.  In Australia
> it's 915 to 928 MHz giving only 13 MHz bandwidth.
>

The RF spectrum neighbour is the Vodaphone GSM uplink allocation.  Voda
> will notice if you impinge on their spectrum, they will complain to ACMA
> and ACMA will come and knock on your door so be careful.  Hence you'll only
> be able to run 5 MHz RF bandwidth (or maybe 10 MHz if not too close to a
> Vodaphone mobile site) and this may defeat the purpose.
>
>
Yep, aware of this, at least as general background - though not necessarily
that they were so militant.



> The lack of gain in your antennas is partly compensated by the reduced
> path loss.  There is 8.5 dB less path loss at 900 MHz compared to 2400.
> 900 MHz will also be less affected by obstructions.  The 900 MHz nanos also
> run pretty high transmit power at +28 dBm giving you another boost.
> Because you will have to run lower RF bandwidth your energy per bit will
> also be higher giving a further boost. (3 to 6 dB compared to running 20
> MHz RF Bandwidth)
>
> The 915-928 band is pretty quiet in most locations around melbourne but if
> you are within 100m or so of a mobile phone tower you may suffer with
> receiver overload with the GSM transmitters nearby at 935 MHz.
>
>
Thanks for the detailed info.  We've been running our 2.4 link at 10MHz
bandwidth some of the time, too, for the same reason - hard to tell if it
really makes that much difference in practice.  It seems that settings we
can change are just tinkering around the edges and the random fluctuations
over the course of a few hours far outweigh any effect our changes make.
Denis has some interesting graphs of link rate and signal strength over
time.


> I suspect you may be able to get a more "stable" link but not necessarily
> with big throughput.
>
>
That's been my suspicion too.


> What kind of TCP/UDP throughput do you get now?
>

Varies rather wildly and unpredictably, as does the signal level.  Best
we've ever seen was a bit over 7Mbps, usually averages about 2-3.  We're
missing an order of magnitude somewhere along the way..

Next steps are either 900MHz, or swap my 18db Yagi for another 24 grid and
try and get some more height and sturdier pole to carry the grid - hence
the present question.

-- 
Dan.
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