archive: SETI Yet another hair-brained-antenna-idea?

SETI Yet another hair-brained-antenna-idea?

rtyndall@juno.com
Sun, 6 Sep 1998 16:31:17 EDT

Yesterday, Rich wrote:
< Greetings my fellow Setizens,
< I recently read a paper somewhere that included a list of past SETI
<searches. As I recall, one of those searches was done with a simple
dipole
<on 1420 Mhz.

Chip N1IR wrote:
*Uhhh. Which one?

Rich replies:
~ Sorry, I've been reading so many papers and abstracts lately
I can't recall.. It may have been a list on a SETI web site. If you
really want to
know, I'll try to find it and post it..

< Now that I've had some time to think about it, it may not be such
<a bad idea.

* It is not a good idea.

~ Yes I agree. It's not a good compromise. It would be far better if we
all owned 6 meter dishes. (Better for what most of us want to do)..

< A dipole (or a 2 turn LH Helix) could cover a lot of the sky.

*That's not a dipole; its a axial mode Kraus helix with quasi-hemi
coverage.

~I agree, a helix is not a dipole. But a helix with a small amount of
gain
would be my choice, even if it wouldn't cover the whole sky at once.
(At least a helix pointed skyward wouldn't see as much ground noise).

~I use the term 'helix' because it's shorter. When I last spoke with
John,
he didn't say "axial mode Kraus helix". He just said "Helix".
So if it's okay with the him, it's okay with me.
(Maybe I should be more careful, I hear Uda killed himself after Yagi
got all the credit)..

< A hand held GPS receiver with a small antenna can easily hear
<weak GPS signals from very high orbits.. (Ranges of 20,000
<to 25,000 km). (My BUD could likely hear a GPS in Lunar orbit).

*yes... but not relevant.

~Maybe not so relevant, but maybe interesting to anyone considering
installing a small antenna.

< My Points:
< We don't know the direction of the incoming signal. (a prime
< reason for the Argus project). We don't know how strong the
< signal will be.. It could be very weak or very strong..
< Maybe a low gain antenna could hear it.

* The transmitted power you would need would be outrageously large.

~True, but not too outrageous if the range was short.

< Benefit #1:
<Those folks who can't install a BUD could increase their participation
<in SETI work. If hundreds of coordinated Non-BUD searchers were to take
<part, a few dB of gain could be added to each site as their numbers
increased.
<(Still maintaining full sky coverage by using assigned declinations).

* But you still won't search the globe by keeping everyone in the same
block...so to speak.

~ If nothing else, some of these low gain stations may eventually
upgrade to BUDs and move themselves off the block a few yl...

< Benefit #2:
< In the event of a very strong short term ETI signal, a few wide field
SETI
< stations around the world might record the hit at the same time.
< That would definitely put ARGUS (everyone) on red alert..

< Benefit #3.
<Although less sensitive, continuous full sky coverage might give us
< a better chance of detecting any Probes (see note) in the local solar
< system area.

* I don't follow this; nor the reason why such probes would use microwave
signalling to us.

~ I can think of one reason right off hand. If an ETI probe studying
earth
knew we were listening on 1420.4056 Mhz, and wanted to be heard..
Of course, a probe might not want to signal us at all..
SETI is like fishing, you may never get a bite or you may get yanked
out of the boat..

<In conclusion:
<One point we have all heard, 'Any coverage is better than none'. If a
<signal was very strong and of short duration, chances of hearing it
with a few dozen
<3 meter dishes is small. A few dozen wide field antennas (in the mix)
might
< give us better odds. If the wide field participants were well
coordinated, (good clocks & LOs)
<their daily data could be collected into one data base and analyzed for
common noise
< peaks & etc. (Who knows what we might find)..?..

*Exceedingly unlikely you will find anything but interference.

~Most of us understand that we are more likely to hit the mega
bucks lottery.. But to be in the pool, you MUST buy a ticket, or the
"Exceedingly unlikely" tends to takes on the value of zero.
(Not that zero is bad mind you.. It's just a little boring)..

~As to interference, it would be great to have the ability to
track down local and orbiting sources of RF inference.
If it worked, this aspect alone might make a low-gain group
a valuable part of the Argus project.

< Note:
<Some Probe theory. Some have estimated that during the next 10 Million
<years, probes (or manned star ships) from Earth could travel to most
<parts of the Milky Way. That is, if they can fly at 0.1 the speed of
light.
<(Plus or minus a few million years for variations in propulsion
technology)..

< Paradoxically speaking, during in the last 10 Billion years, many
<(thousands?) of ET civilizations should have, 'Been there, done that'.
<As the man said "Where's ETI"? They should be here already!
<So the point is, maybe they are. Maybe there are some
<robotic Probes sitting out there in near-earth space scanning the Earth
<for signs of intelligence. ;-)
<Why have they kept silent? That's a good question, maybe they're on a
<schedule. Maybe they only call us for 3 weeks every 15 years..
<Or maybe LDEs are feelers they put out to see what our reaction will
be..?.
<(Did you notice the word 'maybe' appears at random in the above text)?
<This could go on for pages & ages.. Time to go, 73 Rich <>

*Richard, you have failed to compare the spatial figure of merit for
various
low gain/ high gain systems,and looked for the dependence on transmitted
power
(in the scenario you describe). I will give you a hint: the FOM goes as
the
SQUARE ROOT of the transmitted power (among other factors)...that's not
cause
for optimism unfortunately.

~Thanks for the F minus. I just hope my blurb was a little better
reading than the spinning
swimming pool full of Jello with BBs (or whatever).

* The Kardashev 1964 paper considers isotropic transmissions and hence
the
outrageously high powers need for ''Type I,II etc" civs.

~Of course everyone on the list is well aware of Kardashev's 64 (Astron)
paper.
However, that Type III stuff seems really unlikely.. (Harnessing the
energy of a
whole galaxy? 4E37 Watts?). Come on already...
Anyhow, from what I've read Stephenson's 1981 paper shows a more
reasonable
scenario.. And 'isotropic'.. I just don't get it. Why would anyone want
to waste
99.99% of their RF? If I was them, I would get myself a dish. (or a
Helix)..

*Regards,

*Chip N1IR

~Thank you Chip, for expertly pointing out the negative aspects of the
low-gain
idea. Many of us on the list are not experts (especially me) and need to
be
reminded of what mother nature will permit. However, this is a place
where
ideas can be aired, no matter how far-fetched they sound. I just hope
that
others won't be reluctant to post after seeing my poor grade..
(But please no more Jelly pools).. :-)

~73, RIch NJ1A

Richard Tyndall NJ1A Woburn, MA. USA
RTyndall@juno.com or nj1a@erols.com
ARGUS Observatory FN42jl

HEY! I just got a hit!
Darn.. GPS again..
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