archive: Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"

Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"

Dale Lamm ( DaleLamm@worldnet.att.net )
Tue, 29 Dec 1998 23:55:33 -0800

David,

I agree with your observation that terrestrial microwave transmissions
directed
towards stationary satellites would be difficult to detect from great
distances.

Many years ago, I was associated with a company that supplied television

programming to a domestic satellite (USA). We used a ten-meter dish at
the
uplink site. Effeciency was about 50% at 6.0 GHz, gain was around 53dB.
Beamwidth was about 0.35 degrees at the 3 dB down points (quite narrow).

Although the transmitter was capable of putting 3 KW into the feed, the
satellite operators in Vernon Valley, NJ would direct us to run with
somewhat
less than 0.5 KW, to avoid saturating the transponder. On top of that,
the
36 MHz wide analog FM video was dithered at the field rate, to avoid
causing
interference with terrestrial users in the same band. If video were
interrupted,
the dithering signal would insure that there were no "pure" carriers
transmitted.

This is all old technology. Many users (both C band and Ku band) are
moving
to digital modulation schemes. From what I hear, these schemes leave
even
less of a "steady carrier" on which to integrate at the receiver.

DaleLamm@ieee.org