[MLB-WIRELESS] [TIB] A new offer has been added to TIB - 11/1 2/2002

[Craig Sanders]

On Thu, Dec 12, 2002 at 05:53:24PM +1100, evilbunny wrote:
> CS> how does staying *within* legal limits qualify as "cowboy" behaviour?
> CS> we all know what the legal limit is, nobody's suggesting that we can or
> CS> should use amplifiers to exceed that limit.
> 
> Take a read of some of the submissions to the broadband inquiry about
> community groups by commercial operators...

yes, well, some of them are going to lie about us no matter what we do
or say.

all we have to do is make sure we're operating within the legal limit.
not half the legal limit, or a quarter or a tenth of it.


> CS> as long as (card + amp - cable loss + antenna gain) add up to 4W 
> CS> EIRP or less, what's the problem?
> 
> If you don't need the added output why increase for the hell of it?

i never suggested that it should be done for the hell of it.  if nothing
else, it's too expensive to do unless you really need it anyway.

but if you DO need it, if it DOES make a difference to the quality and
utility of your link, i see no reason to dismiss the idea of
amplification without further consideration.  it is one of several
possible options/variables.

> CS> the better the signal i can get from point A to point B, the
> CS> higher the bandwidth - if increasing the output power gets me 5 or
> CS> 11 or even 22Mbps rather than 1 or 2Mbps, then what's wrong with
> CS> that?
> 
> What's wrong is if you have 1000x more signal then needed to achieve
> that result, resulting in anyone past your antenna and desired range
> getting increased amount of noise... Then them sticking up an amp and
> doing likewise to you, and raising your noise floor till your link is
> again useless...

so all these people fussing about using galaxies and building high-gain
antennas (e.g. slotted waveguide omnis or 180 degree antennas) are also
causing problems for everyone else?

i just don't see the difference.

a high-power signal is a high-power signal no matter what the source.
for a receiving antenna, it's the same no matter whether it came from a
high power AP, or a low power AP plus an amplifier or a high-gain
antenna.


> CS> what's the difference between a) using a 500mW card or AP (e.g.
> CS> some of the Demarc units) and b) using a 30mW card or AP plus a
> CS> 500mW amp?  
> 
> Amps usually increases the noise and signal alike, the card is able to
> discriminate against noise and signal without amplifying both
> indiscriminately...

huh?  it looks like you're confusing receive sensitivity with transmit
power.

Tx power is Tx power, no matter where it comes from.  if you have an AP
up a mast, you'll have a few extra inches of cable between the AP and
the amplifier, and two more N connectors.  not enough to introduce any
significant noise or even signal loss.


> CS> why are high gain antennas OK, but amplifiers taboo?
> 
> high gain antenna reduce the beamwidth of signal sent out...
> 
> eg a 15 dBi omni has a beam with of about 3 degrees from memory, where
> as a 6dBi omni with amp outputting at 4W will have a much bigger
> pattern of output cause much more interference to others that you
> either didn't foresee, or at a latter date.

yep, this makes sense.  i agree.  i don't necessarily think it's always
a bad thing, though - in fact, it can be useful characteristic depending
on what you're trying to do.


> As stated before, an amplifier should be the last resort to overcoming
> problems with links, not the first...

i can agree with that too.  however i don't agree that the option should
be automatically dismissed.

craig

-- 
craig sanders <cas at taz.net.au>

Fabricati Diem, PVNC.
 -- motto of the Ankh-Morpork City Watch

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