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Re: This Weekend in Minneapolis: Central States VHF S ociety Meeting

tlangdon@atctraining.com.au wrote:
> 2.4 GHz is _very_ noisy in Melbourne.  Wireless LANs alone can be picked up
> almost anywhere, let alone all the other cordless gadgets out there.

Two things. First:

When Echo was last transmitting on 2.4 GHz I went
driving around Dallas, Texas looking for a quiet
place to setup my satellite station to receive the
downlink. Everywhere I went I could hear a steady
pop-pop-pop noise at about a one-pop-per-second
rate. In some locations there was more than one
popping signal. This is what I hear in my receiver
from the WiFi networks, the cordless phones and
the other spread spectrum transmitters. You wouldn't
want to make analog voice or CW contacts through
this. It's a mess.


I made some recordings of the popping hoping to be
able to make a model the pop waveform and remove it
with some digital signal processing. This won't work.
As Bob and others have noted, the local signals are
tens of decibels stronger than the signals you
are trying to receive from the satellite. The local
"pop" signals completely swamp the receiver while
they are present.

But...the pops are only there for a fraction of a
second albeit a fraction of every second. Much
(most?) of every second *appears* to be clear --
at least in the unscientific limited survey that
I made at my locations. Is this typical?

Has anyone done any measurements to see just
how much we lose to the noises and how much signal
we could still get through in between -- especially
if we go digital and apply some DSP and some
forward error correction (FEC) to this? In the
absence of data showing that this is totally
impossible (or just some data showing that this
is totally not worth the effort!) I would think
of this as a challenge.

I'd like to get several people to make recordings of
their worst local 2.4 GHz noises. I have recording
software you can use. Let's measure. Let's look at
the data and see if there is some solution. If you're
interested, and you have a 2.4 GHz receiver, and you
have a soundcard in your computer, then email me.

Douglas KA2UPW/5
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