[MLB-WIRELESS] Bullet2 output power, why 1W or 100mW

[Kim Hawtin]

Mark Aitken wrote:
> mw at freenet.net.au wrote:
>> Yeah, I can't think of many applications that would need a 1Watt
>> transmitter.  That's not to say that there are no applications for one, just
>> that I can't think of many ;-)
>>
>> 1Watt is about 30dBm, which means that your maximum antenna size is just
>> 6dBi to keep within the 36dB EIRP limit.
>>
>> Now, consider a point to point link of about 50Km.  Theoretically you lose
>> about 135dB signal through the air, so if you start with 26dB at the
>> transmit end, by the time you go 20Km, you only have -99 to work with.  If
>> your antenna is a meagre 6dBi, then the best possible result at the receiver
>> is a measly -93: barely enough to do anything with it.
>>
>> BUT, if you used a 170mW transmitter, which is about 22dBm, then you can use
>> a 14dBi antenna.  So over a 50Km link, you could potentially get -85dBm of
>> signal to the receiver.  That's more likely to produce a reasonably usable
>> result.
>>
>> The only reason I can think of that you would want to use a 1W transmitter
>> would be when you want to do a relatively short hop point to point link
>> (like less than 5Km perhaps), and you wanted to use small, aesthetically
>> unobtrusive, antennas.
>>   
> Or be a Amateur Radio Operator and use the 30dbi into a 24dbi dish 
> giving you 54dbi to play with...gotta love it  :)

After reading the LCD on this, there seem to be issues with the amount of
bandwidth you can use. ie; restricted to 16KHz for a channel. I suppose
there may be more doco that I haven't found yet that allows other options,
but you get that ...

The main problem with using amps with Wifi gear is that you also increase
what ever noise you have too, so you need to have a better sensitivity and
selectivity to deal with this. then you'd modify off the shelf gear, and
it would no longer fit in the ISM 'radio system' class license structure...

its all interesting, but I expect that there are better ways around that
problem =) more sites with more nodes for a start ;)

cheers,

Kim
-- 
Operating Systems, Services and Operations
Information Technology Services, The University of Adelaide
kim.hawtin at adelaide.edu.au