Re: Always poke a dog with a sharp stick

["Edward R. Cole" <al7eb@ptialaska.net>]

See my reply at end of text:

>At 12:43 PM 6/4/00 -0500, Chuck Forster wrote:
>>Where Are We Going?
>>
>>I decided to take a break from unfinished radio astronomy projects and
>>see what others were doing.
>
>>The Seti League is interesting if you like to build equipment, but with
>>85 dishes of a small size, and no visible plan on how to detect real
>>signals, or what to do with the data, I’m not sure where the project
>>will go.
>
>Chuck,
>	You're right, and you're wrong.  
>	First off, according to our website we're now up to 92 small dishes.
>That's up from 5 telescopes just four years ago.  But even that is
>certainly minor progress compared to our grandiose plans (though it
>constitutes more radio telescopes than are currently operated by the rest
>of the world, combined!)  
>	Real signals?  Just how do we define 'real' in the SETI context?  None of
>us really knows how far away the nearest radio-using civilization may be,
>or how powerful their transmitters, so we can only guess as to what kind of
>sensitivity is required to detect real signals.  
>	In the early 1970s, Philip Morrison established a target sensitivity of
>10^23 w/m^2 to do credible SETI.  This figure was published in a NASA book.
> It was his *opinion*.  That happens to have been the sensitivity of the
>late OSU Big Ear when it started its SETI program.  It is also the current
>sensitivity of the average Project Argus station.  It is several orders of
>magnitude below the sensitivity of Arecibo, to be sure, but if it is not
>"real", then neither were Big Ear, or Project Ozma, or any number of the
>earlier SETI experiments.  We could argue the point all day and get
>nowhere, so I suggest we concentrate on your final points.
>
>>what to do with the data, I’m not sure where the project will go.
>
>	What indeed does one do with a mountain of computer data files being
>generated by thousands (or even just under 100) of amateur radio
>telescopes?  Where indeed do we go from here?  We've been grappling with
>that question for five years now.  As The SETI League is an organization of
>volunteers, I turn to our members for answers.  (Many of them seem to think
>that all answers, ideas, direction and guidance should come from me, but
>that's unrealistic.)  
>	My most recent vision for our future direction is expressed in the article
>"Distributed Processing Goes Galactic," which can be seen at
><http://www.setileague.org/articles/galactic.htm> (and is the basis for my
>upcoming talk at SARA 2000.)  But that's just one man's vision.
>	So what's yours?  As a SETI League member, you have a right, and an
>obligation, to share your vision of where the project *should* go.  You can
>dialog on one or more of the various SETI League email lists, send a brief
>guest editorial for SearchLites, or submit a more substantive article for
>our website.  You raise some excellent questions.  I count on you, and your
>1200 fellow SETI League members, to help come up with some excellent answers.
>	73,  Paul

Chuck, Paul, etal:

To start with I don't know if I'd advise one with Chuck's subject title.
Being the owner? of 12 sled dogs [and 12 newly arrived puppies], I'd
suggest "waking a sleeping dog with hamburgers" vs. "poking..."!  In fact
the challenge for any leader of a group is to make sure their is a sample
of "hamburger" occasionally to keep the dog from "sleeping".  As the new
president of our local ham radio club, I'm certainly cognizant of the
effort required with our nearly comatose ham club.

Chuck raises interesting questions, and Paul's article is certainly right
on target.  I won't address the main topic, since software is not my
"hamburger"!  The issue of target signal thresholds-ditto Paul's comment!
The other SETI-League challenge, that of coming up with a practical radio
telescope, is.

As most of you who read the Argus list know, I have recently ordered
components for 21cm, and even so audacious as to publish July, 30, 2000 as
the date it will go on-line [using the 2.57m dish, initially].  But my
first system [the 7cm RT] was much simpler.

Paul talks about reusing old c-band satellite dishes [10-16 foot], which is
really a very realizable approach.  I'd like to suggest a variant, which
might get many more stations going [on 4GHz] with minor expertise/expense.
It's the way I started.

I'm suggesting that initial stations can easily be built from not only the
dish but the c-band LNB/feedhorn.  I know, you're going to say the LNB's
are not stable enough for SETI narrow band requirements.  But hear me out,
first.

I believe [and this is only a theory at present] that those old LNB's
[which generally are pretty good performers with 17-35K noise temp] can be
externally stabilized for both gain and freq.  What I am suggesting is
injecting a phase-gain stable reference signal into the feedhorn input [at
say the upper or lower freq. band edge].  Then the LNB gain/freq variations
may be tracked on this pilot freq. and used to correct the data stream in
the computer.  How would this reference signal be produced?  The SETI 21cm
signal source board [available from DEM] comes to mind.  For this c-band
radio telescope, the 21cm signal would be tripled in a wave guide diode
tripler [short section of w/g bolted between the LNB and the feedhorn].
The w/g section would actually be a cross guide directional coupler which
is easily fabricated with a hacksaw and a small torch.  An optional method
would be to simply radiate the reference signal from the dish center toward
the feed horn.  The tripler could be a simple as a wave guide mounted
diode.  To make the reference better, slaving the xtal oscillator of the
signal source to a GPS reference makes sense [but this is not currently
done very with many Argus stations at this point].  Oh, you might want to
shift the ref. signal to say 1445 MHz [just replace the xtal on the source
board] if you are going to observe at 1420 MHz, as well.

So the newbie can easily [in my opinion] find the old dish, and old LNB
with feed.  What else is needed?  An L-band [950-1450 MHz] receiver and a
computer [in addition to the signal source board, w/g tripler, and some
kind of software].  The computer is easy.  The receiver is the main issue
[same as finding one for 21cm SETI].  As a ham this was easy.  I have a
1296 MHz converter [from DEM] which outputs to a 144-148 MHz [2m ham radio]
receiver.  Another dubious approach is converting an old satellite receiver
[but not easy for the non-technical individual].  Or use a commercial
receiver such as the Icom 7000, 8500, etc.  Probably the use of one of the
PCR1000 type receivers would be easiest.

Well this might not look much better approach than going for a 21cm RT,
unless you already have a c-band satellite TV system the family watches.
You could "steal" it when not in use.  Just save an antenna position on the
Clark belt where there is no satellite, and park the dish there when the TV
is shut off.  Most c-band systems leave continuos power on the LNB even
when the receiver is turned off [to stabilize the LNB].  You would "tee"
off the LNB cable using a TV splitter and run it through an inexpensive
dc-block [also avail. from DEM] and connect to your 1296 MHz convertor or
other receiver running continuously to the computer.

So what if there is no good position without a satellite?  Pick one that
has a couple inactive transponders corresponding to the 1296 MHz IF.  Of
course if your dish is SETI dedicated this is no problem, just point it
away from the Clark belt.

What are the hard parts?  The tripler-wave guide coupler [sounds like a
good subject for a do-it-yourself article], and the software for
compensating the data [I look to Malcom at U of Indiana as a pathfinder,
here, with their LNB temp compensation software].

Might be a few individuals out there still using the old dish for TV that
could use it for "7cm-Argus" sort of like the "screen-saver" approach of
SETI@Home.

So is my LNB stabilized?  Not yet!  But it is a start.  Besides it can be
used as-is for ordinary RA.  My parking position on the Clark-belt is
azimuth 180 [no TV sats west of 172 in Alaska].  Haven't reoriented the
dish, but it will be set to dec=0 [elevation 29.325 and roughly 8.6 deg
above the Clark-belt], since I acquired a new ku-band direct-sat dish for TV.

"Time to feed the dogs!"  Later, Ed


 al7eb@amsat.org 
=================================================== 
50-144-432-1296 
Analog Satellites.
2m-eme: FT-847-MGF1801-4xM2xpol-20 (V/H)...125w brick 
	...building 8877 (QRV?) 
23cm-eme: DEMI xvtr & preamp-K9EK(7211)=125w-45 Loop, Soon!
	...OE9PMJ(TH328)=500w & 5m dish (delayed till Fall 2000?) 
21cm-Radio Telescope: 2.57m dish (July 30, 2000) 
	...move to 5m dish this Fall. 
13cm: 2.57m dish...Drake LNB for 2401 Rx
7cm-Radio Telescope: 2.57m dish-25K TVRO LNB-1296 IF
3cm-eme:  2.57m dish...DEMI xvtr & DB6NT w/g preamp 
	...(Rx tests Summer 2000)(Need TWTA)
=================================================== 
ARRL-ASM-AMSAT*-SETI*-SARA...*Alaska Coordinator