Subject: (Fist) Re (et al) Satellite dish risks??? (fwd)
Date: Sun, 9 May 1999 044845 -0500 (CDT)
From: "Roy L. Beavers" <rbeavers@llion.org>
To: emfguru <rbeavers@llion.org>
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---------- Forwarded message ----------
Date: Sun, 09 May 1999 12:52:10 +1000
From: Stewart Fist
To: "Roy L. Beavers"
Subject: Re: (et al) Satellite dish risks??? (fwd)
I would be very surprised if anyone could measure any significant output from
a recieve-only satellite dish at distance of more than a few inches.
The intermediate stage and the oscillator which produce the hetrodyne
frequency would only be apparent at the output of the Low Noise Block
Convertor (LNBC) which is a very, very, high quality amplifier which sits
directly behind the satellite dish. There would be no significant IF
frequency feeding back to the dish, and any that did, would be projected
straight back at the satellite like a searchlight.
The job of the LNBC is to amplify the very, very low-level signal collected by
the dish, and the reason it is mounted so close behind the dish is because it
must amplify those tiny signals before they collect too much stray
interference from the surrounding environment, and from the molecular movement
of the copper wire itself. We are dealing with extraordinarily minute
power-levels here at the input stages to these LNBC amplifiers.
So if such an amplifier wasn't completely protected from signal ingress
(inward flows from the surrounds), it would be totally ineffective. What
applies to ingress, also generally applies to egress (outward emission). If
the LNBC is shielded in a way which stops unwanted signals getting in, then it
is likely to be highly effective at stopping those inside from getting out.
Also the cable carrying this IF signal down to the set-top box is designed the
same way. It must be high efficiency coaxial, shielded all the way to block
the unwanted entry (and therefore the exit) of extraneous signals.
The only possibility I can see for signal emissions from such a dish is that
the IF oscillator on some LNBCs may be housed separately and be inadequately
shielded, but I think this would be classed by the installers as a fault
(probably due to a broken earth or something).
--
Stewart Fist - writer and columnist
See http://technology.news.com.au/opinion/
http://www.abc.net.au/http/sfist/ (some archives)
http://www.electric-words.com (main archives)
70 Middle Harbour Road, Lindfield, 2070, N.S.W, Australia
Phone +61 2 9416 7458 Fax +61 2 9416 4582
Archive provided courtesy of WaveGuide, http://www.wave-guide.org
Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html