On Jun 20, 10:45 am, Jim Lux wrote:
On Jun 19, 11:20 am, Robert Clark wrote:

On Jun 16, 6:57 pm, Robert Clark wrote:

From: (Robert Clark)
Date: 23 May 2001 11:15:06 -0700
Subject: Will amateur radio astronomers be the first to directly
detect extrasolar planets?
Newsgroups: rec.radio.amateur.space, rec.radio.amateur.antenna,
sci.astro, sci.astro.seti, sci.space.policyhttp://groups.google.com/group/sci.astro.seti/browse_frm/thread/c0018...

The long wavelengths should make the requirements for accurate
distance information and timing synchrony between the separate
detectors easy to manage even for amateur systems.

Not easy, not for the precision required.
You need not only precise time (straightforward), but also precise
location (not so straightforward)

You're interested in roughly 20MHz, as I recall. Wavelength of 15
meters. In time, about 45 nanoseconds.

Let's start with a real relaxed requirement, comparable to the mirror
flatness for a telescope of lambda/14. That means a time knowledge
of about 3 ns and a position knowledge of 1 meter, in absolute terms.

Typical GPS receivers that have a 1pps output are good to about 20-30
nanoseconds. Using that to discipline a quartz oscillator, you can do
a bit better, but it's non trivial to get to the 1-2 ns range.
Remember, you're also planning on integrating over time, so you have
to hold that tolerance for a long time.

It would be difficult to determine your position to an absolute
accuracy of 1 meter, much less the phase center of the antenna (which
will change as a function of the angle of incidence, quite
substantially, unless you're putting those dipoles up 100s of feet in
the air.

Using this method

might make the detection achievable even if the power or transmitting
antenna size requirements are not practical for a low cost, low weight
lander on the Moon for an individual detector on Earth.
The recent achievement of real-time very long baseline interferometry
should make it possible to integrate these separate detector signals
in real-time as well:

snip

You need to go beyond looking at press releases from radio
astronomers.

However, instead of using the satellite TV dishes, we could use
individual dipole antennas attached to each house. You would need to
communicate high data rates for the signals detected so you would need
broadband internet access for this.
These dipole antennas as per the Radio JOVE project are just simple
vertical wires so could be attached to the house when the installer is
connecting the wiring for the broadband. Possibly you could use the
same external wiring as for the broadband but that might cause
interference with the internet signals.

Radio Jove uses a pair of horizontal dipoles connected together to
create a single narrower lobe pointing up.

As shown on the Radio JOVE page the receivers for these dipole
antennas are quite simple so would contribute minimally to the cost of
installation.

Who's paying, and how minimal? I don't think so.

You do need accurate positional determination and timing

synchrony for each receiving system to do the very long baseline
interferometry, but at these decametric wavelengths this would be easy
to do with GPS receivers carried by the installers.

No they can't. You need position accuracy of sub-1 meter accuracy,
and that isn't achievable by simple handheld devices, like your Garmin
E-trex, etc. A surveyor using a survey GPS system can get there,
although absolute position (relative to, say, the center of the earth,
or some standard datum) to 1 meter would be very challenging.

There's also the not so little problem of tidal bulge. Your position
changes in absolute (relative to a stellar reference) terms several
tens of cm. On top of that, tectonic plate movement is on the order of
several cm/year, which is in the same general ballpark as your
accuracy requirement.

...

The NASA Global Differential GPS System.
"The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system.
"Employing a large ground network of real-time reference receivers,
innovative network architecture, and award-winning real-time data
processing software, the GDGPS System provides decimeter (10 cm)
positioning accuracy and sub-nanosecond time transfer accuracy
anywhere in the world, on the ground, in the air, and in space,
independent of local infrastructure."
http://www.gdgps.net/

This would be enough for the positional accuracy at this wavelength.
This type of highly accurate receiver would probably have to be used
only by the installers as they are likely to be expensive. Perhaps the
positional accuracy could be maintained over time by referring to a
satellite signal.
The "time transfer" accuracy mentioned apparently does mean the many
different sites can be put in time synchrony to within sub-nanosecond
precision by reference to the atomic clocks on several GPS satellites
at the same time:

Global Positioning System.
2.) Basic concept of GPS
* 2.1 Position calculation introduction
* 2.2 Correcting a GPS receiver's clock
http://en.wikipedia.org/wiki/Global_...concept_of_GPS

Innovation: GPS Time Transfer.
Using Precise Point Positioning for Clock Comparisons.
Nov 1, 2006
By: François Lahaye, Diego Orgiazzi, Patrizia Tavella, Giancarlo
Cerretto.
GPS World
http://www.gpsworld.com/gpsworld/Inn.../detail/383189

However, JPL radio astronomer Dr. Dayton Jones responded to my
question about the required timing accuracy at such long wavelengths,
suggesting it might only have to be only at the ten's of nanoseconds
to even microseconds range, depending on the bandwidth being detected:

Newsgroups: rec.radio.amateur.space, rec.radio.amateur.antenna,
sci.astro, sci.astro.seti, sci.space.policy
From: (Robert Clark)
Date: 18 Jun 2001 10:26:50 -0700
Subject: Will amateur radio astronomers be the first to directly
detect extrasolar planets?
http://groups.google.com/group/sci.a...56d6bc52a09590

Note that with the Radio JOVE system the bandwidth being detected is
usually quite small at the tens to hundreds of khz range, as the
emissions consist of short pulses. This would only require timing
accuracy at the microsecond range.
For the cost, note that for cable, DSL, satellite, internet and/or TV
service typically the receivers, modems, routers, etc are only
"rented" where you pay a nominal fee every month. If the cost for the
dipole and receivers were in the range of $100 dollars per
installation then this could be amortized over the life of that
broadband internet system, at say $1 dollar a month or even 50 cents a
month.


Bob Clark