[MLB-WIRELESS] [TIB] A new offer has been added to TIB - 11/12/2002

[Greg Wright]

I have seen some 802.11b amplifiers in testing, and they do indeed CAP
the output. I never did learn how the device knows what entenna you
have, but Im of the understanding that you have to enforce the antenna
gain to stay legal via a control on the amp.

I can ask more about them if anyone *really* wants to know and cant look
for yourselves :o)

-----Original Message-----
From: Tony Langdon [mailto:tlangdon at atctraining.com.au] 
Sent: Thursday, 12 December 2002 10:20 AM
To: 'Craig Sanders'; evilbunny
Cc: melbwireless at wireless.org.au
Subject: RE: [MLB-WIRELESS] [TIB] A new offer has been added to TIB -
11/12/2002


> you missed my point.
> 
> my point was that they don't increase the output *BY* 1 Amp.  they 
> change it *TO* 1 Amp regardless of the input signal strength.  i.e. 
> it's
> *not* cumulative with the original Tx power.

Come on guys, let's at least get the termonoligy right! :-)  For a
start, power is measured in Watts, not Amps.  Current consumption is
measured in amps (more correctly called Amperes).

Now, an amplifier has what is called "gain".  Depending on the design of
the amplifier, this gain may remain relatively constant, regardless of
input level (in which case, the amplifier is said to be linear - hey,
this is where the CB term "linear" comes from!), or the gain may change
with input level (non-linear - common in FM transmitters because of
their higher efficiency).

Now, I'm no expert on 802.11b modulation techniques, so I don't know if
the power amplifiers are linear or not, but I do know that if you vary
the drive, you WILL vary the output in some way (tuned up enough
transmitters to know that one :) ).

However, some amplifiers may have automatic power control, so the power
is limited to the rated output over a wide range of drive level.  Again,
I do not know.

At this point, we need someone who actually knows specifically about
802.11b amplifiers.

> > No, they amplify the signal and noise alike... They don't increase 
> > sensitivity, if anything they reduce it due to increased noise...
> 
> some claimed to increase sensitivity.  whether that's truth
> or marketing
> lie is something that testing would tell.

This depends on two things.  Firstly, the noise figure of the receive
preamplifier in the unit.  If it has a lower noise figure than the input
stage of the wireless card, you will generally get some improvement in
sensitivity.

Secondly, where you place the amplifier will have a big impact.  If it
has a receive preamplifier, then locating it as close to the antenna as
possible means that the receive signal gets amplified before the lossy
coax.  This can make a considerable improvement to the received signal.
This is the same principle between masthead preamplifiers in TV and
amateur radio installations - put the gain before the lossy feedline.

So on the question of receive improvement, the true answer is "it
depends".
:)

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