archiv~1.txt: SETI Re: Fwd: Computer Radios and Noise

SETI Re: Fwd: Computer Radios and Noise

Noel C. Welstead ( (no email) )
Sat, 20 Mar 1999 07:21:31 +1000

Dear Ralph,

By virtue of the fact that "All" computers exhibit very noisy environments
from the switch mode power supplies to the crystal oscillators that drive
the logic. You only need to place an AM receiver next to any computer
to hear the noise. The monitor is also a vast source of QRM that radiates
over a long distance.

When you combine all this noise with a very sensitive receiver with high gain
LNA's connected, you are probably going to get low level signals in the
background noise (static) that will appear when you integrate over a long
enough time span. This type of extremely low level interference will eventually
turn itself into a Peak on the DSP display.

Microwave Seti, by virtue of its nature, is the search for extremely low
level signals buried in the noise. This is exactly what you will see when
you use a radio receiver living inside a computer. No amount of
shielding will stop all the noise from having some impact on the detection
process utilized by our software methods.

At Radio Astronomy sites around the world, every effort is made to
reduce the noise from computers. They are very noisy, so I guess that
putting a Radio inside a computer is like placing a geophone in the
ground under Grand Central Station and expecting to hear those
faint murmuring from the shifting blocks that make up the crust of
our fair planet.

Don't get me wrong, the WinRAdio product is a great idea and has
it's place in the world of radio. I just don't think that it's a great way
to do Seti. Rich Tyndall occasionally posts some interesting snippets
from his experiences with noise from GPS birds and they are hundreds
of miles away. Internal noise from a computer is much closer.

I would recommend that any project Argus station go to great lengths
to reduce the probability of a false Hit by paying attention to shielding
and providing a noise free environment that will give you every chance
of detecting those ever so weak signals. Even place your computer
monitor inside a shielded enclosure just to make sure.

Earth everything and put it all in a metal box or rack with doors. My
dish is directly above the workshop and there is a piece of Aluminium
foil rolled out in the ceiling cavity to reduce any stray signals from
stuff in the garage. I found that stray signals could get into the feed
horn from my workshop by reflection from other metallic objects
in and around the garage and yard, so the foil reduced this quite
a bit.
Hope this helps.

Regards Noel C. Welstead
SETI League Volcor Eastern Australia.

RGittleman@aol.com wrote:

>
>
> ------------------------------------------------------------------------
>
> Subject: Computer Radios
> Date: Fri, 19 Mar 1999 10:43:49 EST
> From: RGittleman@aol.com
> To: nmelstead@seti.org.au
>
> I read your article with great interest on the potential noise problems with
> equipment such as the WinRadio unit. I raised the same question with the the
> company several months ago and their response was they had not experienced a
> problem with computer generated noise. Do you have any test data on the
> WR-3100i or similar equipment ?
>
> Ralph Gittleman