On Jun 16, 6:57 pm, Robert Clark wrote:
On another forum there was debate about whether the requirement of
"near real time" high definition video transmissions was achievable
for a such a low-cost mission.
It would certainly be doable if the receiving antennas on Earth were
the large radio antennas used for space communications with
interplanetary probes or those radio antennas used for radio
astronomy. This is evidenced by the fact that the Kaguya(Selene) lunar
orbiter mission was able to send high definition video to a large
receiving dish radio antenna. And also by the fact that DirecTV sends
high definition video to only 2 foot size antennas from geosynchronous
orbit; so 10 times larger antennas would be able to receive such
signals from a 10 times larger distance at the Moon.
However, I was wondering if it would be possible to detect this using
amateur sized equipment at such a large distance. Usually for
receiving high data rates you used transmissions at very high
frequencies, as higher frequencies can carry more data. For instance
both Kaguya and DirecTV transmit the high def video at gigahertz
frequencies.
However, for the system I'm imaging I'm thinking of using much lower
frequencies, and necessarily longer wavelengths. What I wanted to do
is transmit at decametric wavelengths. High data transmissions rates
would be achieved by making it be pulsed in an on-off fashion at high
intensity but at a rapid rate.
On that other forum the data rate required for high def TV was given
as 256,000 bits per second. So I wanted to make these transmissions be
pulsed at this rapid rate at wavelengths of a few tens's of meters.
My decametric wavelength requirement was because of the fact that
high schools and universities have programs for detecting radio
emissions from Jupiter at these wavelengths:

NASA's Radio JOVE Project.http://radiojove.gsfc.nasa.gov/

The Discovery of Jupiter's Radio Emissions.
How a chance discovery opened up the field of Jovian radio studies.
by Dr. Leonard N. Garciahttp://radiojove.gsfc.nasa.gov/library/sci_briefs/discovery.html

These school and university receiving antennas on Earth consist of
dozens to hundreds of vertical dipoles of lengths at the meters scale
to correspond to the radio wavelengths. Some questions I had: how
intense would the pulse have to be on the Moon to be detectable from
the Moon above background noise for a detector on Earth of say a few
dozen dipoles? Could this be done for the transmitter of power of say
a few hundred watts for a low cost, low weight lander mission? Could
the transmitter antenna on the moon be only a few meters size for the
low weight requirement?
A secondary purpose I had in mind was a pet project of mine involving
linking these many school receivers to form a global telescope at
decametric wavelengths:

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. 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:

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


In this post I suggested using DirecTV's and other satellite TV
companies receiving dishes for SETI:

Newsgroups: sci.astro.seti, sci.astro, rec.radio.amateur.space,
sci.physics
From: (Robert Clark)
Date: 7 Feb 2005 15:07:03 -0800
Subject: Could DirecTV satellite dishes be used for the Square
Kilometer Array - and a more radical proposal[ Can DirectTV-type
satellite dishes be used for SETI?]
http://groups.google.com/group/sci.a...25e5339227855a

In the discussion in that thread there were mentioned several
problems with that proposal (possibly fixable with some expensive
retrofits) but one big problem is that satellite TV is not designed to
be two-way. Some satellite services are two-way when they are also
used for internet access, but this is a much smaller proportion of the
satellite TV subscribers.
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.
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. 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. Over time you
could keep the systems in synchrony by timing stamps accessed over the
internet.
I suggested before using 10 million dipoles world-wide for detecting
Jovian-sized planets close in to their primaries out to perhaps 10
light-years. According to this page, over 16.6 million new broadband
internet users came online just in one quarter this year alone,
bringing the number of broadband users world-wide to 429 million:

More people worldwide are subscribing to high-speed Internet
connections.
China and other Asian countries among the growth leaders.
http://www.nationmultimedia.com/2009...y_30105358.php

New broadband subscribers would automatically get the dipole
antennas. At the rate of increase of broadband subscribers, it would
only take 3 months to reach 10 million separate dipoles. If each
installer when setting up a new system, also retrofitted an another
existing broadband system, then you could reach the full coverage of
all the broadband subscribers dipoles in 6 years.
The number of world-wide broadband subscribers will be 500 million by
2010. At current growth rates it would be 900 million within the 6
years it took to equip each broadband subscriber system with one of
the antenna dipoles. This is nearly two orders of magnitude better
sensitivity than a 10 million dipole system. You could detect out to
100 light-years, opening up many more stars to the possibility of
detection.



Bob Clark