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

[Rob Clark]

FYI - here is an online Link Budget calculator.

http://store.freenet-antennas.com/linkbudget.php

Cheers

Rob

-----Original Message-----
From: melbwireless-bounces at wireless.org.au
[mailto:melbwireless-bounces at wireless.org.au] On Behalf Of Kim Hawtin
Sent: Wednesday, 4 March 2009 10:19 AM
To: 'Melbourne Wireless'
Subject: Re: [MLB-WIRELESS] Bullet2 output power, why 1W or 100mW


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
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