Can DirectTV-type satellite dishes be used for SETI?

In article ,
Matt Giwer wrote:

It is feasable if the combination of 1 and 2 do not result in more than about 1/36th wavelength

That's about 6 times better than the requirements for dishes [A]. I don't
know where you got that figure from, but it is wrong.

error. The more it deviates from that the less useful. 1/36th would cover about a 10 degree circle

Er! 1/36th in the beam direction would cause a deviation of the order of
(in radians) 1/(36 * baseline length in wavelengths) in the direction
of the individual fringes. The direction in which the fringes are
intended to coincide would only see a small reduction in in-phase
signal.

Whilst I strongly suspect that differential and carrier phase will not
solve the problem, it is nothing like as bad as you suggest.

in the sky. And that would indicate the array gain, roughly log(180^2/10^2). At 1/4 wavelength error

If the peak to peak error is 1/4 wave, in the worst possible configuration,
the array gain will be degraded by 3dB.

[A] Generally the profile accuracy suggested for dishes is 1/10th to 1/12th
of a wavelength, but the phase error is doubled by the reflection.

David Woolley wrote:
In article ,
Matt Giwer wrote:

It is feasable if the combination of 1 and 2 do not result in more than about 1/36th wavelength

That's about 6 times better than the requirements for dishes [A]. I don't
know where you got that figure from, but it is wrong.

A dish is summing power. You don't care much. It could be less if the receiver at the focal point
were larger but at some point the receiver blocks too much incoming signal.

In a distributed array you must have phase information so you can determine the direction it is
pointing. If we assume these dishes are all pointing with zero error at the satellite 32,000 miles
up from all over the US (for example) they are all pointing at a different point at infinity. So if
you want to look at a point at astronomical distances you have to correct for the satellite aim point.

Consider a dozen widely spaced antenna pointed at the same satellite. They go on to point to widely
different points in space as they "pass through" the satellite. That gives you no gain at all, it
does not not improve the signal to noise ratio.

To take the data from all of them and sum the data from one point in the sky, Tau Ceti the odds on
favorie, you have to phase shift the data from all of them such that you are only considering the
part of the signal that corresponds to that direction.

Because television sensors all converge on a very local point 32,000 miles away (36,000 mile orbit
from the center and varying by latitude) the "aim point" rapidly diverges beyond the satellite. To
recombine that noise into useful data you have to know how to "point" it to a single direction to
combine signal to exceed the noise.

Given the reality that only the dishes in a very small town can be considered to be pointing to
roughly the same point in deep space there is no gain of interest as the smaller the town the
smaller the deep space area and the lesser the gain.

Two dishes one mile apart exactly pointing to the same point 32,000 miles up point to greatly
different places in deep space.

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wrote:

Methods of fixing your position within millimeters using GPS exist as
long as you can make a comparison to the GPS signals received at a site
whose position is known within millimeters. This precisely known site
can be kilometers away. This is used in surveying for example:

This is a good start. Is it affordable to calibrate every installation? These sites are by
definition on houses and such and installed by people who know only how to do that. So each has to
be properly calibrated.

CARRIER-PHASE TRACKING
"Carrier-phase tracking provides for a more accurate range resolution
due to the short wavelength (about 19 centimeters for L1 and 24
centimeters for L2) and the ability of a receiver to resolve the
carrier phase down to about 2 millimeters. This technique has primary
application to engineering, topographic, and geodetic surveying and
may be employed with either static or kinematic surveys. There are
several techniques that use the carrier phase to determine a station's
position. These include static, rapid-static, kinematic, stop-and-go
kinematic, pseudokinematic, and on-the-fly (OTF) kinematic/Table 8-4
lists these techniques and their required components, applications,
and accuracies."
http://cartome.org/FM3-34/Chapter8.htm

This would suffice for centimeter wavelengths.

BUT the transmission of the data back to the processing source has to be perfect. It cannot be by
raw cable as that would require a separate network and if it existed people would use cable for TV
not satellites. It has to be processed data going back and then we have local computers and data
packets and delays all piling up. Most of those can be overcome. Even if there were raw data fibers
going back to the processor, the length of the fiber path has to be known exactly to preserve phase
information.

--
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in an insane conspiracy by Iraq against the US?
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In article ,
Matt Giwer wrote:

A dish is summing power. You don't care much. It could be less if the receiver at the focal point

Mathematically (and because of the linearity of EM fields with respect to
superimposition, dishes sum field (volts/metre) not power. In fact dishes
can be treated as the limiting case of phased arrays, with infinitesimal
elements (and free space phasing lines); that's how you work out the beam
pattern to get the approximate gaussian (the actual one for a circular
aperture is, I believe, a Bessel function). Using analogue delay lines
for phasing is standard for stacked arrays and, with switchable loops,
even for some electronically steerable ones. (Dishes do combine power
overall, but so do delay line phased arrays, and you can only work out
beam patterns by considering the phased integration of the fields.)

However, one doesn't need to think about dishes to demonstrate that even
quarter wave peak to peak along the beam direction only compromises by
3dB. (Perpendicular to the beam, there is no effect.)

The worst case configuration is with half exactly an eighth wave high and
half an eighth wave low. The in-phase components follow a cosine pattern
and are + and - 45 degrees. Cos (45 degrees) is sqrt (2). The out of phase
components follow a sine pattern and cancel. Squaring to get power, one
gets a factor of 2, i.e. 3dB. Note that I haven't made any assumptions
about the array size, here, except that the individual element capture
areas don't overlap.

Whilst I have severe doubts as to the ability to phase to even this accuracy,
it is 9 times coarser than the 1/36th you were claiming, and has only
halved the effective number of elements.

David Woolley wrote:
In article ,
Matt Giwer wrote:

A dish is summing power. You don't care much. It could be less if the receiver at the focal point

Mathematically (and because of the linearity of EM fields with respect to
superimposition, dishes sum field (volts/metre) not power.

Correct. Sonar background myself. Never did quite learn to think in E-M terms for posting purposes.

In fact dishes
can be treated as the limiting case of phased arrays, with infinitesimal
elements (and free space phasing lines); that's how you work out the beam
pattern to get the approximate gaussian (the actual one for a circular
aperture is, I believe, a Bessel function). Using analogue delay lines
for phasing is standard for stacked arrays and, with switchable loops,
even for some electronically steerable ones. (Dishes do combine power
overall, but so do delay line phased arrays, and you can only work out
beam patterns by considering the phased integration of the fields.)

However, one doesn't need to think about dishes to demonstrate that even
quarter wave peak to peak along the beam direction only compromises by
3dB. (Perpendicular to the beam, there is no effect.)

The worst case configuration is with half exactly an eighth wave high and
half an eighth wave low. The in-phase components follow a cosine pattern
and are + and - 45 degrees. Cos (45 degrees) is sqrt (2). The out of phase
components follow a sine pattern and cancel. Squaring to get power, one
gets a factor of 2, i.e. 3dB. Note that I haven't made any assumptions
about the array size, here, except that the individual element capture
areas don't overlap.

Whilst I have severe doubts as to the ability to phase to even this accuracy,
it is 9 times coarser than the 1/36th you were claiming, and has only
halved the effective number of elements.

And again correct. I was thinking in terms of a linear sensor array not an area sensor array. Area
would proportional to the square the linear accuracy required in the lesser direction. My error was
a hangover from my earliest work.

Regret the delay in responding.

--
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amount of time and in the same order. There is no
evidence they are independent.
-- The Iron Webmaster, 3365

"Joseph Lazio" wrote in message
[....]
RD I'm not a total expert in this field, but know enough to be
RD dangerous..

RD If I'm not mistaken, to phase correlate N elements, you do not
RD need to phase-correlate all N^2 baselines, but (after
RD time/phase-adjusting each of the individual N signals to intended
RD beam direction), you can simply create a correlator tree of 2-1
RD phase correlators. The tree would then consist of N correlators,
RD which counts for linear complexity of computation power.

No, one does have to multiply the signals from all N antennas
together, which is roughly an N^2 problem. The issue in radio
astronomical interferometry is that the "visibility" or "correlation
coefficient" is a measure of the Fourier transform of the sky
brightness. Every unique pair of antennas gives one "visibility," so
one wants to obtain all possible visibilities from the N antennas.

Might it be that we are talking about two different correlations..?

I was talking about a simple phase-correlator : accumulate signals
from all elements. In hardware, that is done with 'phase-splitters'.
(At least that's how I hooked my 4 loop-yagi's together back in the old days).
Antenna phase-splitters are passive devices which simply 'add' the electrical
field of multiple feed-points (or split them if you are transmitting).

For a (digitally sampled) antenna signal, these would be simply be 'adders'
which need to 'add' the signal value for each element for each sample.

For one beam, for 10Ghz sample rate (5 GHz bandwidth), and N elements,
you would need to do 10*10^9 * N additions per second (pretty large
amount of digital adders), but it is linear w.r.t. N.

I think you might have been talking about a smarter technique to do this work.


RD Question for Joe : Which part of the SKA system would be the
RD bottleneck in computational effort, and create a problem even in
RD 2020 ?

Actually, the correlator, as difficult as it is, may not be the
limiting factor for the SKA computation. Some people think they know
today how to build an SKA-level correlator.

The most prominent concern has been how does one make an image? The
SKA is envisioned as having a large field of view (e.g., 1 deg^2 at 1
GHz, and some people are concerned that that's not large enough). In
order to make high-quality images, one probably has to image that
entire field of view with something approaching 0.1 arcsecond
resolution. Thus, a single image would be something like 10,000 x
10,000 pixels in size, and that's only for a single frequency. One
probably has to utilize multiple frequencies simultaneously, in order
to defeat some other effects. Moreover, current processing of radio
interferometric images is an iterative process, in which one makes an
image, corrects it for certain effects, makes a new image, improves
the corrections, makes a new image, ....

Interesting...


There's a memo floating around discussing all of these aspects of
processing. IIRC, the conclusion was that the processing power
required to make high-dynamic range images scaled as the dish diameter
(which sets the field of view) as something like D^6 or D^8. Thus,
all other things being equal, just changing from the 25-m VLA dishes
to the proposed 12-m US SKA dishes would increase computation by a
factor of 64 to 256, and that's even without taking into account the
much larger number of antennas.

I should say that not everybody agrees with this analysis, but it is
recognized that the computational aspects of the SKA may be
significant.

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"RD" == Rob Dekker writes:

RD "Joseph Lazio" wrote in message [....]

RD If I'm not mistaken, to phase correlate N elements, you do not
RD need to phase-correlate all N^2 baselines, but (...), you can
RD simply create a correlator tree of 2-1 phase correlators. The
RD tree would then consist of N correlators, which counts for linear
RD complexity of computation power.

No, one does have to multiply the signals from all N antennas
together, which is roughly an N^2 problem. The issue in radio
astronomical interferometry is that the "visibility" or
"correlation coefficient" is a measure of the Fourier transform of
the sky brightness. Every unique pair of antennas gives one
"visibility," so one wants to obtain all possible visibilities from
the N antennas.

RD Might it be that we are talking about two different
RD correlations..?

Potentially. Your comment about a "tree" perhaps should have clued me in.

RD I was talking about a simple phase-correlator : accumulate signals
RD from all elements. In hardware, that is done with
RD 'phase-splitters'. (At least that's how I hooked my 4 loop-yagi's
RD together back in the old days).

I'd call that a beam former.

The Very Large Array (and other interferometers of its ilk) work by
combining the signals from all unique pairs of antennas.
Specifically, one takes the signals from antennas #1 and #2, multiples
them together, and then integrates for a short time. That's the
measured quantity, often called a "visibility" or "correlation
coefficient." One then repeats this for antennas #1 and #3, antennas
#1 and #4, #1 and #5, #1 and #6, ..., until one has made all unique
combinations from 27 antennas. (Those who enjoy math problems can try
to figure out how many such combinations there are.

To make it even more complicated, some of the designs for the Square
Kilometer Array (and the Low Frequency Array and the Long Wavelength
Array and others) contemplate using both beam formers and correlators.
Thus, one would start with a bunch of dipoles. The signals from a
"small" number of dipoles (e.g., 100) would be combined in the manner
you described. This produces a signal typically called a "station"
beam or "pod" beam. The signals from various stations (numbering
perhaps 100) are then combined by a correlator.

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Another possible problem is that I'm not even sure the receivers that
come with the satellite dishes can even detect frequencies other than
the 12 Ghz the satellites broadcast at.
In regard to the wavelengths that the .5 m antennas could usefully
collect, I've seen references that a dipole antenna should be a quarter
of the wavelength. Is this different for parabolic antennas?
I'm thinking perhaps you could simply attach flat metal dipoles to the
surface of the .5 meter antennas so they could collect megahertz
frequencies. Then at a quarter wavelength you could collect down to 2
meter wavelengths or 150 Mhz.
While we're at it, the thought of using dipoles, like TV antennas,
raises another possibility. You need receivers for these frequencies.
Where could we get large numbers of receivers already existing at these
frequencies? Inside TV's! Assuming we could solve the problem of
tranmitting the data to a central site (ultra wideband, broadband over
power-lines, amateur packet radio, etc.), we could have all new TV's
come installed with a circuit that transmits received signals to the
central site. The number of new TV's sold yearly worldwidde is 90
million. This would result in markedly larger numbers of possible
receivers even above the satellite TV approach.
There might be privacy issues with this idea however.


Bob Clark


Robert Clark wrote:
A.) According to this article $1.4 billion dollars is earmarked to be
spent on the Square Kilometer array with completion expected by 2015:

Radio Astronomy Will Get a Boost With the Square Kilometer Array.

http://www.universetoday.com/am/publ...a.html?1592004

As I stated below the primary extra components to be added to the
DirecTV dishes to be used for radio astronomy are the feedhorn and
the
preamp. The feedhorn is simply a metal pipe of little cost. The
SetiLeague site lists sellers of specially made preamps for SETI
search at $150. But these are handmade. From the low number of
circuit
elements, I estimate that if mass produced at the millions of items
level the price could come down in the range of $10 each.
This site states the rate of growth of satellite TV subscribers is
at
4 million per year:

Satellite TV Basics.
http://www.satellitetv-hq.com/hqguid...tv-basics.html

This means the *receivers* for the SKA system if using these
satellite dishes could be installed in 1 year at an extra cost of $10
x 4,000,000 = $40 million dollars. Note that the feedhorn and the
preamp could be attached at manufacture would not cost more on
installation labor. The installation is already paid for by the
satellite TV subscribers. To pay for the extra cost for the added
equipment you could simply add $1 extra per month to the subscriber
rate. Then these 4 million, .5 meter wide dishes would have a total
collecting area of a disk 2000 x .5 m = 1000m = 1km wide, the total
collecting area expected for the SKA. Moreover this would have the
advantage that an additional square kilometer of collecting area
would
automatically be added every year over several years going by the
present growth rate.
You could also attach the extra equipment to the 25 million
satellite
systems already installed in perhaps 4 or 5 years. The number of
satellite TV subscribers worldwide was 60 million in 2003 and is
expected to grow to 100 million by 2008:

Digital Satellite TV Platforms Continue to Gain Subscribers, and
Profits are on the Rise.
http://www.instat.com/press.asp?ID=1171&sku=IN0401236MB

If this many .5 meter antennas were networked together, they would
have the collecting area of a single antenna 10,000 x .5 m = 5 km
wide.

Note that the idea of using over 50 million separate, stationary
elements is one of the proposals being considered for the SKA
architectu

Aperture Array (AA)
http://www.skatelescope.org/pages/design_nl.htm

This method of keeping the receiving antennas fixed while detection
directions are determined electronically is called the phased array
approach and has the advantage that many separate targets can be
observed simultaneously. It also has the advantage that interfering
local signals can be suppressed. However, the Aperture Array has
antennas close together in a predetermined configuration with the
positions precisely determined. How could this work for the randomly
positioned satellite dishes?
Methods of differential GPS and carrier phase synthesis now have the
capability of determining position to within millimeters. The method
compares the GPS signal between a precisely known site and an unknown
site to locate the unknown site to within centimeters. Then a
comparison is made in the actual phase of the signals received at the
two sites to locate the unknown site to within millimeters:

CARRIER-PHASE TRACKING
"Carrier-phase tracking provides for a more accurate range resolution
due to the short wavelength (about 19 centimeters for L1 and 24
centimeters for L2) and the ability of a receiver to resolve the
carrier phase down to about 2 millimeters. This technique has primary
application to engineering, topographic, and geodetic surveying and
may be employed with either static or kinematic surveys. There are
several techniques that use the carrier phase to determine a
station's
position. These include static, rapid-static, kinematic, stop-and-go
kinematic, pseudokinematic, and on-the-fly (OTF) kinematic/Table 8-4
lists these techniques and their required components, applications,
and accuracies."
http://cartome.org/FM3-34/Chapter8.htm

This should be sufficient for keeping the signals for the millions
of
antennas in phase up to perhaps 3 cm wavelength, 10 Ghz frequency.
Timing synchronization can be obtained by synchronizing from the
common signal received by the dishes from the satellite.
The Argus telescope at Ohio State University (this is different from
Project Argus operated by The Seti League) may provide a model for
how
sensitive such a system can be operating from noisy populated areas:

Newsgroups: sci.astro.seti
From: Bob Dixon
Date: Wed, 19 May 2004 12:49:02 -0400
Subject: The Argus Telescope

http://groups-beta.google.com/group/...df1f29f629f20/

Argus Expands the Search For Life.
By Daniel Sorid
posted: 03:30 pm ET
09 June 2000
http://www.space.com/searchforlife/s...us_000609.html

Note though that the continent wide satellite dish system will have
an advantage over Argus in dismissing unwanted signals in that such
signals would only be detected by a local group of antennas not the
continent wide system.

In mentioning an estimated price for this system, I emphasized the
estimate was for the *receiving* part of the system. But of course
for
such a system of separate receivers, it is just as important to
combine and process the signals.
In the thread for DirecTV being used for SETI, someone mentioned you
might need to transfer 1 Gbps from each antenna for detections at 12
Ghz. I seem to recall that analog signals can be tranferred in
greater
density than digital signals. Perhaps the signal received by each
antenna can be transmitted in analog form with a stamp indicating its
location and time of origin.
For examples of the data density required we could look at some
examples of systems of separate antennas that have been used to give
combined signals in *real time*:

Astronomers Demonstrate a Global Internet Telescope.
Date Released: Friday, October 08, 2004.
http://www.spaceref.com/news/viewpr.html?pid=15251

This produced data of 32 Mbits/second for each telescope for
observations at 1.6 Ghz. So at 16 Ghz perhaps 320 Mbps might be
expected for each antenna. The data was sent over a high-speed
internet network available to universities that operates at gigabits
per second. Within a few years, the data transfer rate is expected to
reach tens of gigabits per second.

And:

Prototype SETI Antenna Array Will Help Radio Astronomers Too.
Date Released: Wednesday, June 07, 2000.
http://www.spaceref.com/news/viewpr.html?pid=1992

This is of the Argus telescope at Ohio State University. The 64
antennas here detect signals from 400 to 2000 Mhz. The antennas
together produce 2.56 gigabytes per second, or 20.48 gigabits per
second. So each telescope produces 320 Mbps. This article states that
no physical connection could economically carry that much data over
distance however this was written in 2000. Ultra wideband technology
(mentioned below) now has that capability.

For processing the data for the proposed SKA system, I expect the
distributed computing system used by Set@Home to be used, wherein
millions of computers take part in the calculations. As for how the
data can be sent by the individual antennas, there are a few possible
ways the signals could be combined.

1.)DirecTV offers a two-way broadband satellite internet service
called DirecWay. This allows signals to be sent from the home
antennas
back up to the transmitting satellite. However, this system currently
has only a 100,000 subscribers in place. I want to use the millions
of
subscribers using the satellite TV systems. I think a minor low-cost
modification of the current TV antennas would also allow them to
transmit to the satellites used for broadband internet service. (I
don't think the satellites used for TV service can be used to receive
signals.)

2.)Another possibility for transferring the data from each antenna
might be to use military satellites currently used for surveillance
on
radio transmissions, perhaps using satellites that were
decommissioned
and are no longer used for sensitive military tasks.

3.)Possibly the techniques used with amateur packet radio could be
used. Here radio links are used to setup data networks analogously to
how the internet sets up data transfer networks using the TCP/IP
protocols:

N6GN's Microwave Link Page
http://www.sonic.net/~n6gn/uwavelink/uwv.html

INEXPENSIVE MULTI-MEGABAUD MICROWAVE DATA LINK
http://www.sonic.net/~n6gn/hr89/uwvarticle.html

4.)Ultra wideband (UWB) promises gigabit data transfers over both
cable and wireless connections and should be available this year
(2005):

New chipset promises gigabit broadband on cable and wireless.
Rupert Goodwins
ZDNet UK
May 11, 2004, 15:20 GMT
http://news.zdnet.co.uk/communicatio...9154271,00.htm

Ultrawideband in 2005, but only in America
Rupert Goodwins
ZDNet UK
February 19, 2004, 09:45 GMT

http://news.zdnet.co.uk/communicatio...9146644,00.htm

Ultrawideband: Wireless Whoopee.
08:34 AM Oct. 09, 2004 PT
"SAN FRANCISCO -- Think of it as Wi-Fi on steroids. On its way to
U.S.
living rooms and maybe even automobiles is a new type of high-speed
wireless connection that promises downloaded data rates of up to 1
gigabit per second -- roughly 18.5 times the speed of Wi-Fi -- to
personal computers and other devices.
"This ultrawideband technology, which could become available in the
next two years, also allows the devices to send data upstream to a
network at 480 megabits per second."

http://www.wired.com/news/technology...w=wn_tophead_3

5.)Some public utilities now collect their meter readings from radio
transmitters attached to their meters. The data is collected by
receiver on utility poles and then transmitted to a central site.
This
method could be adapted to work for collecting the data from the
separate antennas.

6.) The above methods would require that the data transmissions be on
specified frequencies that will not be used for detections. However,
another method might not have this limitation:

Broadband Over Power Lines?
01:15 PM Feb. 09, 2003 PT
"ST. LOUIS -- Coming to a home or office near you could be an
electric
Internet: high-speed Web access via ubiquitous power lines, of all
things, making every electrical outlet an always-on Web connection."
http://www.wired.com/news/technology...,57605,00.html

This is a new technique already being tested in small markets to
provide interent service over power lines. The speed of transmission
can be ramped up to 1 gigabits per second using ulta wideband
technology.

B.)This last leads me to another proposal for large scale separated
antennas for radio astronomy: using the electrical wiring in
households as radio antennas. Here's a post to
rec.radio.amateur.antenna discussing this:


================================================== ========================
From: Ed Hare, W1RFI )
Subject: ISO info about using house wiring as a TV antenna
Newsgroups: rec.radio.amateur.antenna
Date: 2000-12-29 15:33:06 PST

Richard Friday wrote in message
...

I know this post might be off-topic but could find no other
newsgroup that
had "antenna" in its name. I'd be most appreciative if someone
could point
to a more suitable discussion or other source of information.
I've seen advertised a device that claims to allow you to use the
electrical wiring of your house as a tv antenna. You plug this
device
into an outlet, and then use connections it provides as your tv
antenna.
I'm trying to find out if this actually works but have not been
able to
find any reviews.

This device will receive some signals. However, house electrical
wiring is
not a very good VHF antenna system for a couple of reasons:

First, it is very difficult to predict the direction that the house
wiring
will best receive from. It is quite likely that the antenna pattern
will
have all sorts of peaks and nulls, sort of as if you had a rotatable
TV
antenna that was pointing in several directions at once. This may
not
pick
up much of the TV signal you want to pick up or may have multiple
responses,
resulting in ghosts.

Also, an electrical power line can be a very noisy place. All sorts
of
electronic devices on the line, from power-line equipment itself to
every
motor or power supply plugged in near you may create noise that will
interfere with the signal you want to receive.

If you have no other antenna choice, that device may be useable, but
I
don't
think it will work as well as a good set of "rabbit ears" on top of
your TV.

Ed Hare, W1RFI

================================================== ========================

The disadvantage of the electrical wiring going in several different
directions may actually be an advantage in regards to a SETI search
since you would want the detections to be omnidirectional. If there
are 100,000,000 homes which average 10 meters across then this would
result in a collecting area of 10,000 x 10 meters = 100 km across.
Since you would want to include large commercial establishments, the
size would actually be larger than this.



Bob Clark


wrote in message
roups.com...
I was interested to read this on the Seti League web site:

__________________________________________________ ________
Parasitic SETI
Dear Dr. SETI:
As a Satellite dish owner and a strong interest in SETI, I was
wondering if anything is available to allow the home satellite dish
owner to 'search' when he is not watching TV. I do a bit of
programing
and would love to help make it so home dish owners could do this.
Is it
possible? What would it take? Does the dish have to follow a spot
or
can it sweep the sky from a fixed position? If this is possible it
could add a million listeners to the system.

Bill T.

The Doctor Responds:
Absolutely, Bill! Parasitic SETI with a home satellite TV dish is
not
only feasilble, it's widely practiced. A second feedhorn and preamp
assembly are mounted next to the C-band horn/LNB at the apex of the
dish (see Figure 2 of this article). This assembly feeds the rest
of a
SETI system (see our online Tech Manual). You can then sweep out
the
sky, as described here. And yes, a million participants would be
nice,
but our goal is a more modest 5000 stations.
__________________________________________________ ________
http://www.setileague.org/askdr/parasite.htm

I believe they are referring to the 6 ft. backyard type antennas,
judging from the linked images on the page. But could the roof
mounted
DirectTV and Dish Network type antennas be used for SETI?
The mentioned extra equipment are an extra feedhorn and a
preamplifier. The feedhorn can made cheaply but the preamp seems
expensive. If these preamps were mass produced for this purpose
could
their per item cost be brought under $50?
I'm envisionig a government agency such as NSF, or a scientically
interested billionaire, paying satellite TV companies to attach
this
extra equipment to their satellite dishes. Say $100 million is
earmarked for the program. Then you would want the extra cost to be
under $100 for each dish for say 1,000,000 subscribers. Judging
from
the diagram in the online Tech Manual linked to on the page, the
other
equipment should be doable by the equipment that comes with the
satellite TV system. Computer processing would be done separately
at a
central location.
If you had a 1,000,000 of these .5 meter wide antennas it would
have
the detection sensitivy of a single antenna 500 meters wide.
Bob Clark

"RC" == Robert Clark writes:

RC Another possible problem is that I'm not even sure the receivers
RC that come with the satellite dishes can even detect frequencies
RC other than the 12 Ghz the satellites broadcast at. In regard to
RC the wavelengths that the .5 m antennas could usefully collect,
RC I've seen references that a dipole antenna should be a quarter of
RC the wavelength. Is this different for parabolic antennas?

The rule of thumb is that the dish should be more than about 6
wavelengths across, or diffraction starts to become really important.
Thus, for instance, the VLA (25 meter diameter), when operated at 74
MHz (4 meter wavelength), is right on the hairy edge.

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On a sunny day (21 Feb 2005 12:24:20 -0800) it happened "Robert Clark"
wrote in
.com:

Another possible problem is that I'm not even sure the receivers that
come with the satellite dishes can even detect frequencies other than
the 12 Ghz the satellites broadcast at.
In regard to the wavelengths that the .5 m antennas could usefully
collect, I've seen references that a dipole antenna should be a quarter
of the wavelength. Is this different for parabolic antennas?
I'm thinking perhaps you could simply attach flat metal dipoles to the
surface of the .5 meter antennas so they could collect megahertz
frequencies. Then at a quarter wavelength you could collect down to 2
meter wavelengths or 150 Mhz.
While we're at it, the thought of using dipoles, like TV antennas,
raises another possibility. You need receivers for these frequencies.
Where could we get large numbers of receivers already existing at these
frequencies? Inside TV's! Assuming we could solve the problem of
tranmitting the data to a central site (ultra wideband, broadband over
power-lines, amateur packet radio, etc.), we could have all new TV's
come installed with a circuit that transmits received signals to the
central site. The number of new TV's sold yearly worldwidde is 90
million. This would result in markedly larger numbers of possible
receivers even above the satellite TV approach.
There might be privacy issues with this idea however.


Bob Clark


Robert Clark wrote:
A.) According to this article $1.4 billion dollars is earmarked to be
spent on the Square Kilometer array with completion expected by 2015:

Radio Astronomy Will Get a Boost With the Square Kilometer Array.

http://www.universetoday.com/am/publ...a.html?1592004

As I stated below the primary extra components to be added to the
DirecTV dishes to be used for radio astronomy are the feedhorn and
the
preamp. The feedhorn is simply a metal pipe of little cost. The
SetiLeague site lists sellers of specially made preamps for SETI
search at $150. But these are handmade. From the low number of
circuit
elements, I estimate that if mass produced at the millions of items
level the price could come down in the range of $10 each.
This site states the rate of growth of satellite TV subscribers is
at
4 million per year:

Satellite TV Basics.
http://www.satellitetv-hq.com/hqguid...tv-basics.html

This means the *receivers* for the SKA system if using these
satellite dishes could be installed in 1 year at an extra cost of $10
x 4,000,000 = $40 million dollars. Note that the feedhorn and the
preamp could be attached at manufacture would not cost more on
installation labor. The installation is already paid for by the
satellite TV subscribers. To pay for the extra cost for the added
equipment you could simply add $1 extra per month to the subscriber
rate. Then these 4 million, .5 meter wide dishes would have a total
collecting area of a disk 2000 x .5 m = 1000m = 1km wide, the total
collecting area expected for the SKA. Moreover this would have the
advantage that an additional square kilometer of collecting area
would
automatically be added every year over several years going by the
present growth rate.
You could also attach the extra equipment to the 25 million
satellite
systems already installed in perhaps 4 or 5 years. The number of
satellite TV subscribers worldwide was 60 million in 2003 and is
expected to grow to 100 million by 2008:

Digital Satellite TV Platforms Continue to Gain Subscribers, and
Profits are on the Rise.
http://www.instat.com/press.asp?ID=1171&sku=IN0401236MB

If this many .5 meter antennas were networked together, they would
have the collecting area of a single antenna 10,000 x .5 m = 5 km
wide.

Note that the idea of using over 50 million separate, stationary
elements is one of the proposals being considered for the SKA
architectu

Aperture Array (AA)
http://www.skatelescope.org/pages/design_nl.htm

This method of keeping the receiving antennas fixed while detection
directions are determined electronically is called the phased array
approach and has the advantage that many separate targets can be
observed simultaneously. It also has the advantage that interfering
local signals can be suppressed. However, the Aperture Array has
antennas close together in a predetermined configuration with the
positions precisely determined. How could this work for the randomly
positioned satellite dishes?
Methods of differential GPS and carrier phase synthesis now have the
capability of determining position to within millimeters. The method
compares the GPS signal between a precisely known site and an unknown
site to locate the unknown site to within centimeters. Then a
comparison is made in the actual phase of the signals received at the
two sites to locate the unknown site to within millimeters:

CARRIER-PHASE TRACKING
"Carrier-phase tracking provides for a more accurate range resolution
due to the short wavelength (about 19 centimeters for L1 and 24
centimeters for L2) and the ability of a receiver to resolve the
carrier phase down to about 2 millimeters. This technique has primary
application to engineering, topographic, and geodetic surveying and
may be employed with either static or kinematic surveys. There are
several techniques that use the carrier phase to determine a
station's
position. These include static, rapid-static, kinematic, stop-and-go
kinematic, pseudokinematic, and on-the-fly (OTF) kinematic/Table 8-4
lists these techniques and their required components, applications,
and accuracies."
http://cartome.org/FM3-34/Chapter8.htm

This should be sufficient for keeping the signals for the millions
of
antennas in phase up to perhaps 3 cm wavelength, 10 Ghz frequency.
Timing synchronization can be obtained by synchronizing from the
common signal received by the dishes from the satellite.
The Argus telescope at Ohio State University (this is different from
Project Argus operated by The Seti League) may provide a model for
how
sensitive such a system can be operating from noisy populated areas:

Newsgroups: sci.astro.seti
From: Bob Dixon
Date: Wed, 19 May 2004 12:49:02 -0400
Subject: The Argus Telescope

http://groups-beta.google.com/group/...df1f29f629f20/

Argus Expands the Search For Life.
By Daniel Sorid
posted: 03:30 pm ET
09 June 2000
http://www.space.com/searchforlife/s...us_000609.html

Note though that the continent wide satellite dish system will have
an advantage over Argus in dismissing unwanted signals in that such
signals would only be detected by a local group of antennas not the
continent wide system.

In mentioning an estimated price for this system, I emphasized the
estimate was for the *receiving* part of the system. But of course
for
such a system of separate receivers, it is just as important to
combine and process the signals.
In the thread for DirecTV being used for SETI, someone mentioned you
might need to transfer 1 Gbps from each antenna for detections at 12
Ghz. I seem to recall that analog signals can be tranferred in
greater
density than digital signals. Perhaps the signal received by each
antenna can be transmitted in analog form with a stamp indicating its
location and time of origin.
For examples of the data density required we could look at some
examples of systems of separate antennas that have been used to give
combined signals in *real time*:

Astronomers Demonstrate a Global Internet Telescope.
Date Released: Friday, October 08, 2004.
http://www.spaceref.com/news/viewpr.html?pid=15251

This produced data of 32 Mbits/second for each telescope for
observations at 1.6 Ghz. So at 16 Ghz perhaps 320 Mbps might be
expected for each antenna. The data was sent over a high-speed
internet network available to universities that operates at gigabits
per second. Within a few years, the data transfer rate is expected to
reach tens of gigabits per second.

And:

Prototype SETI Antenna Array Will Help Radio Astronomers Too.
Date Released: Wednesday, June 07, 2000.
http://www.spaceref.com/news/viewpr.html?pid=1992

This is of the Argus telescope at Ohio State University. The 64
antennas here detect signals from 400 to 2000 Mhz. The antennas
together produce 2.56 gigabytes per second, or 20.48 gigabits per
second. So each telescope produces 320 Mbps. This article states that
no physical connection could economically carry that much data over
distance however this was written in 2000. Ultra wideband technology
(mentioned below) now has that capability.

For processing the data for the proposed SKA system, I expect the
distributed computing system used by Set@Home to be used, wherein
millions of computers take part in the calculations. As for how the
data can be sent by the individual antennas, there are a few possible
ways the signals could be combined.

1.)DirecTV offers a two-way broadband satellite internet service
called DirecWay. This allows signals to be sent from the home
antennas
back up to the transmitting satellite. However, this system currently
has only a 100,000 subscribers in place. I want to use the millions
of
subscribers using the satellite TV systems. I think a minor low-cost
modification of the current TV antennas would also allow them to
transmit to the satellites used for broadband internet service. (I
don't think the satellites used for TV service can be used to receive
signals.)

2.)Another possibility for transferring the data from each antenna
might be to use military satellites currently used for surveillance
on
radio transmissions, perhaps using satellites that were
decommissioned
and are no longer used for sensitive military tasks.

3.)Possibly the techniques used with amateur packet radio could be
used. Here radio links are used to setup data networks analogously to
how the internet sets up data transfer networks using the TCP/IP
protocols:

N6GN's Microwave Link Page
http://www.sonic.net/~n6gn/uwavelink/uwv.html

INEXPENSIVE MULTI-MEGABAUD MICROWAVE DATA LINK
http://www.sonic.net/~n6gn/hr89/uwvarticle.html

4.)Ultra wideband (UWB) promises gigabit data transfers over both
cable and wireless connections and should be available this year
(2005):

New chipset promises gigabit broadband on cable and wireless.
Rupert Goodwins
ZDNet UK
May 11, 2004, 15:20 GMT
http://news.zdnet.co.uk/communicatio...9154271,00.htm

Ultrawideband in 2005, but only in America
Rupert Goodwins
ZDNet UK
February 19, 2004, 09:45 GMT

http://news.zdnet.co.uk/communicatio...9146644,00.htm

Ultrawideband: Wireless Whoopee.
08:34 AM Oct. 09, 2004 PT
"SAN FRANCISCO -- Think of it as Wi-Fi on steroids. On its way to
U.S.
living rooms and maybe even automobiles is a new type of high-speed
wireless connection that promises downloaded data rates of up to 1
gigabit per second -- roughly 18.5 times the speed of Wi-Fi -- to
personal computers and other devices.
"This ultrawideband technology, which could become available in the
next two years, also allows the devices to send data upstream to a
network at 480 megabits per second."

http://www.wired.com/news/technology...w=wn_tophead_3

5.)Some public utilities now collect their meter readings from radio
transmitters attached to their meters. The data is collected by
receiver on utility poles and then transmitted to a central site.
This
method could be adapted to work for collecting the data from the
separate antennas.

6.) The above methods would require that the data transmissions be on
specified frequencies that will not be used for detections. However,
another method might not have this limitation:

Broadband Over Power Lines?
01:15 PM Feb. 09, 2003 PT
"ST. LOUIS -- Coming to a home or office near you could be an
electric
Internet: high-speed Web access via ubiquitous power lines, of all
things, making every electrical outlet an always-on Web connection."
http://www.wired.com/news/technology...,57605,00.html

This is a new technique already being tested in small markets to
provide interent service over power lines. The speed of transmission
can be ramped up to 1 gigabits per second using ulta wideband
technology.

B.)This last leads me to another proposal for large scale separated
antennas for radio astronomy: using the electrical wiring in
households as radio antennas. Here's a post to
rec.radio.amateur.antenna discussing this:


================================================= =========================
From: Ed Hare, W1RFI )
Subject: ISO info about using house wiring as a TV antenna
Newsgroups: rec.radio.amateur.antenna
Date: 2000-12-29 15:33:06 PST

Richard Friday wrote in message
...

I know this post might be off-topic but could find no other
newsgroup that
had "antenna" in its name. I'd be most appreciative if someone
could point
to a more suitable discussion or other source of information.
I've seen advertised a device that claims to allow you to use the
electrical wiring of your house as a tv antenna. You plug this
device
into an outlet, and then use connections it provides as your tv
antenna.
I'm trying to find out if this actually works but have not been
able to
find any reviews.

This device will receive some signals. However, house electrical
wiring is
not a very good VHF antenna system for a couple of reasons:

First, it is very difficult to predict the direction that the house
wiring
will best receive from. It is quite likely that the antenna pattern
will
have all sorts of peaks and nulls, sort of as if you had a rotatable
TV
antenna that was pointing in several directions at once. This may
not
pick
up much of the TV signal you want to pick up or may have multiple
responses,
resulting in ghosts.

Also, an electrical power line can be a very noisy place. All sorts
of
electronic devices on the line, from power-line equipment itself to
every
motor or power supply plugged in near you may create noise that will
interfere with the signal you want to receive.

If you have no other antenna choice, that device may be useable, but
I
don't
think it will work as well as a good set of "rabbit ears" on top of
your TV.

Ed Hare, W1RFI

================================================= =========================

The disadvantage of the electrical wiring going in several different
directions may actually be an advantage in regards to a SETI search
since you would want the detections to be omnidirectional. If there
are 100,000,000 homes which average 10 meters across then this would
result in a collecting area of 10,000 x 10 meters = 100 km across.
Since you would want to include large commercial establishments, the
size would actually be larger than this.



Bob Clark


wrote in message
groups.com...
I was interested to read this on the Seti League web site:

__________________________________________________ ________
Parasitic SETI
Dear Dr. SETI:
As a Satellite dish owner and a strong interest in SETI, I was
wondering if anything is available to allow the home satellite dish
owner to 'search' when he is not watching TV. I do a bit of
programing
and would love to help make it so home dish owners could do this.
Is it
possible? What would it take? Does the dish have to follow a spot
or
can it sweep the sky from a fixed position? If this is possible it
could add a million listeners to the system.

Bill T.

The Doctor Responds:
Absolutely, Bill! Parasitic SETI with a home satellite TV dish is
not
only feasilble, it's widely practiced. A second feedhorn and preamp
assembly are mounted next to the C-band horn/LNB at the apex of the
dish (see Figure 2 of this article). This assembly feeds the rest
of a
SETI system (see our online Tech Manual). You can then sweep out
the
sky, as described here. And yes, a million participants would be
nice,
but our goal is a more modest 5000 stations.
__________________________________________________ ________
http://www.setileague.org/askdr/parasite.htm

I believe they are referring to the 6 ft. backyard type antennas,
judging from the linked images on the page. But could the roof
mounted
DirectTV and Dish Network type antennas be used for SETI?
The mentioned extra equipment are an extra feedhorn and a
preamplifier. The feedhorn can made cheaply but the preamp seems
expensive. If these preamps were mass produced for this purpose
could
their per item cost be brought under $50?
I'm envisionig a government agency such as NSF, or a scientically
interested billionaire, paying satellite TV companies to attach
this
extra equipment to their satellite dishes. Say $100 million is
earmarked for the program. Then you would want the extra cost to be
under $100 for each dish for say 1,000,000 subscribers. Judging
from
the diagram in the online Tech Manual linked to on the page, the
other
equipment should be doable by the equipment that comes with the
satellite TV system. Computer processing would be done separately
at a
central location.
If you had a 1,000,000 of these .5 meter wide antennas it would
have
the detection sensitivy of a single antenna 500 meters wide.
Bob Clark

I am just a humkble electronics person with several years experience with
sat dishes.. and software (I write).
2 things bother me about the proposal (topic)
1)
The smaller the dish, the worse the signal to noise (lower signal level),
and you mostly will be in the noise.
2)
polarization, sat dish LNBs come hor or vert polarized, and perhaps circular.
What will it be.
If you only use the dish and your own preammp what will it be made of?
10 Ghz = 3 cm wavelength.
Remember the dishes are used to receive from only 40000km or a little more
away, and then get 'acceptable' signal to noise.
The sats transmits several watts of power.
For astronomy you will likely want to be a few orders of magnitude more
sensitive.
Liquid cooled parametric preamps for the amateur?
What am I missing here?