Re: [amsat-bb] WiFi users "may" try AO-40, look out!

[Phil Karn <karn@xxxxxxxxxxxxxxx>]

>Yes, the card was spec'ed at -94 dBm at the 1 megabit rate and after
>measuring and calibrating with some good attenuators and spectum analyzer
>we were surprised that in fact, we measured the knee in the error rate
>within a fraction of a dB of that very point.

But what was the system noise temperature? You need that to compute
the required S/No. That in turn will tell you if a low-noise preamp
would help, or if you're already being limited by the demodulator's
inherent performance.

The system noise temperature consists of the noise temperature of the
source (300K, if it included attenuators at room temperature) plus the
unknown noise temperature of the receiver front end.

The next step is to add enough calibrated noise to the test signal to
be sure of swamping the receiver's own noise so you can measure the
S/No performance of the demodulator separate from the front end.  From
that and your -94dBm figure, you can compute the noise temperature of
the receiver front end.

Phil
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