archive: Re: SETI Some Questions

Re: SETI Some Questions

Dr. H. Paul Shuch ( (no email) )
Mon, 31 Aug 1998 09:24:49 -0400

At 08:43 AM 8/31/98 -0400, Peter J. Thompson wrote:

> I understand that one of the goals of Project Argus stations is to cover
the frequency range 1420 - 1660 MHz. Maybe I missed it in some of the
online documentation but is it the intent that each station be capable of
scanning this entire range or are individual sites assigned a smaller chunk
of spectrum?

It would be nice if everybody could cover the entire specturm.
Realistically speaking, individuals will scan whatever frequency range they
can or choose to cover. Remember that our members are all volunteers. We
can recommend, but not require any specific capabilities.

> Are the stations that are downconverting scanning the same amount of
spectrum as those that have micowave-capable receviers?

Probably not.

>What are the tradeoffs involved here?

Cost is always the limiting factor, isn't it?

> From what I've seen of the converter lierature etc, it appears that
downconversion is taking place after the microwave signal has been fed from
the feedhorn/LNA via cable to the location of the radio equipment.
Wouldn't it be better to place the converter at the feedpoint and pipe a
vhf or hf signal to the shack? Is this what I've seen referred to as an LNB?

We've had a lot of discussion of this just in the past week on the email
lists. Mounting the converter outside poses some major environmental
problems. Whereas a TVRO LNB can drift several MHz and still work fine
with its wideband signals, we are doing FFT to 10 Hz bins, so any thermally
induced LO drift more than a couple of Hz will hurt us. Since gain
sufficient to overcome feedline losses is cheap at L-band, we consider it
better to do the downconversion inside. (BTW, the DBS receivers pipe an
L-band IF thru the coax.)

> As far as digital signal processing is concerned, is everybody still
doing the DSP part at audio frequencies? What is the state of the art
concerning DSP chips these days? Can we expect to be doing DSP at the IF
some day soon? With 400MHz PC's generally available, I've got to believe
there are some super fast but probably (still) expensive DSP chips available.

See my MiniMETA artical at <http://www.setileague.org/articles/minimeta.htm>.

Regards, Paul
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H. Paul Shuch, Ph.D. Executive Director, The SETI League, Inc.
433 Liberty Street, PO Box 555, Little Ferry NJ 07643 USA
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