[MLB-WIRELESS] wifi cards for sale

[Tony Langdon, VK3JED]

At 03:11 PM 5/11/2010, mw at freenet.net.au wrote:
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>Hi Shaun,
>
>Therein lies the danger – some 900MHz cards are 
>down-converted 802.11g, so you use the 802.11g 
>drivers and select from the normal set of channels 1 thru 13.

These won't be legal in AU (see below).

>
>Inside the device, it translates those channels 
>to some 900MHz spectrum.  The problem is that 
>you have no guarantee that the channel 1 on the 
>802.11g scale is within the 915 – 928 MHz range 
>(or any other channel selection of course)

One would want to know how the channels are laid 
out, to ensure that you can find one in the ISM band. :)

>
>Odds are very much ON that several of those 
>channels would be outside the allowed range 
>since they are separated by 5MHz, and there 
>simply isn’t enough width in that 900MHz class 
>license band to fit them all in! ;-)

Well, the 2.4 GHz is 83 MHz wide, and the 900 MHz 
band is only 13 MHz wide, so there's a lot less room.

>
>In fact many of them will allow you to select 
>below and/or above the legal range.  If the 
>drivers allow you to choose by frequency, at 
>least you have a reasonable chance of avoiding 
>trouble from the ACMA.  Motorolla canopy 900MHz 
>product is notorious for this – it allows the 
>user to select as low as 908 (from memory) and 
>well inside the Vodafone licensed band.  I know 
>of two wireless ISPs that have been nicked for 
>doing that, and I’m sure they are not alone! ;-)

The proper way to do it is have what a lot of 5 
GHz products have, namely a setting for 
"regulatory domain", which applies limits to what 
channels can be selected, so by setting it to 
"Australia", you are (supposedly) guaranteed a 
channel set that fit in the 915 - 928 MHz 
range.  Even setting by frequency has its own 
pitfalls.  If you don't know the bandwidth of the 
signal, it's still quite easy to be operating 
illegally, while your nominal carrier frequency 
is well inside the band.  Let's take the case of 
a downconverted 102.11g signal.  The 802.11g 
signal is 22 MHz wide, so it's IMPOSSIBLE to 
operate this legally on 900 MHz, it simply won't 
fit within the 13 MHz available.  In the past, 
900 MHz gear had lower speeds, to allow their 
signals to fit inside the available bandwidth.


>Cost one of them $15K fine for a second offense 
>– they could lose their carrier license for a third! :-o

Ouch! :D


73 de VK3JED / VK3IRL
http://vkradio.com