EME (Moonbounce), SETI (The Search for Extraterrestrial Intelligence) and Radio
Astronomy can be regarded as various forms of Weak Signal Communication.
Weak Signal Communication techniques are under severe assault by a wide
variety of conditions and demands of an ever expanding technological and
commercialized Society.
The parts of the Electro Magnetic Spectrum that were historicly
allocated to Amateur Radio represent a large treasure. International
and National Commercial Interests are making continuous efforts
to chip away frequencies.
It is good to remember that Amateur Radio received these bands
in the very early beginnings of radio and that there is
no Constitutional Right to these bands.
Even the Internationally Protected Frequency Bands for Radio Astronomy
are becoming more and more polluted by spurious signals generated by
low orbitting satellites.
These forms of pollution might affect the ability to execute SETI operations
in the future. Spread Spectrum Communication in particular will
present ans ever increasing thread to weak signal conditions.
When Measuring "Weak" or Small Signals in Electrical Circuits,
one will eventually reach the point at which such a signal can no be
longer Recognized as the Desired Signal. The signal is now of the
same order of magnitude as the The Natural Noise in the system.
The Total Noise has many components such as Sky Noise, and Antenna System Noise, Cable Losses and Noise in the the Receiver.
More on the 400
MHz skynoise by AA7FV/G3SYS.
In Radio Astronomy as well as in Weaksignal loss as well as Signal is often expressed
in degrees Kelvin, the so called Noise Temperature.
Relatively small changes in either the level of noise temperature
or in the signal amplitude, can cause large changes in the so
called Signal to Noise Ratio. This in turn can largely affect
the ability to Detect the desired signal or not in the presence of Noise.
Since the discovery of "Radio", a part of the radio amateur
community has been attracted to do their communicating and observing under
these Weak Signal conditions. It is also in this region with its
Natural Noise Floor where one can observe many interesting phenomena in
circuitry and wave propagation.
In the past and present Radio Amateurs have explored and discovered new forms of
propagation, often by applying Weak Signal Procedures.
Real Weak Signal Enthusiasts can experience the thrill by participating
in these techniques in particular by receiving and monitoring signals, generated
by nature and mankind at the noise threshold level.
It is as important to preserve clean, unpolluted EM spectrum for Radio as it
is for other forms of observing such as optical astronomy.
It is safe to assume and to state that Signals from Other Civilisations,
existing or not, will appear as weak signals at best.
EME ( Moonbounce )
This Technique represents to most Radio Amateurs a very special branch of
Weak Signal Communication, due to the Limitations on Antenna Size and
Transmitter Power Output.
In Moonbounce, the Moon Surface is used as a Reflector for Radio Signals and
the echoed signals that return to Earth are often just barely above the Noise Background.
EME is, as are other forms of Weak Signal Communication such as Meteor Shower (MS)
and forms of Satellite Communication, a big Challenge to its Devotees.
Because the technique is often marginal, all sections in the system have
to work near to or at their peak performance level.
Such Sections of importance are among others:
Listen to Echo Tests by PA0EPD (From Bram, SM0FLY's page )
Because many of these requirements overlap with the ones for Amateur Radio Astronomy and SETI, it makes sense, in the opinion of this author at least, to learn about these fields as well. An Example of such an Integrated Environment, being it Educational and Professional, can be seen at Radio Science at Stanford.
Microwave
Frequencies for Weaksignal Frequency bands for Weaksignal
Communication are most frequencies assigned to the Amateur Radio
Service. From 1.7 MHz to 28 MHz conditions exist at times and area's
where communication is possible very close to the natural noise floor.
The 50 MHz band presents many opportunities with many devotees.
When going up in frequency the properties change and Space
Communication Applications become an important player.
Microwave Bands from 1.2 GHz and up are rapidly becoming in demand
for commercial applications. The radio amateur community is at
great risk of loosing the assigned frequency bands. Microwaves present
lots of possibilities for Weaksignal work, EME, SETI and Radio Astronomy.
Radio Astronomy is the Science of Astrophysics in the radio spectrum. From Low Frequencies to as high as 300 GHz. Many bodies radiate in addition to signals in the Visible, signals over the total Electro Magnetic Spectrum. Bodies appear as sources of noise in the frequency domain. The measurement of the type, quantity and location of these sources of radiation form the observational part in Radio Astronomy.
SETI or the Search of Extraterrestrial Intelligence is the Science of
Detecting Intelligent Signals from other Civilisations. This science forms
a controversial subject in certain circles. Whatever your views are, the Search efforts
are right in line with Advanced Weaksignal Detection and Techniques.
A large body of Scientific Literature is available on the Internet.
Interesting Reading material forms SETI Pioneers by David W. Swift.
Bottom line is that many Weaksignal stations could utilize their sophisticated
stations in SETI and get more return on effort and investment.
By participating in the
Search one would be part of a World Wide Network of mainly
radio amateurs, searching in the Universe for Weak Signals.
Digital Signal Processing
is a way of Detection Enhancement. Analog Techniques exist side by side with digital
techniques.
The event of powerful home computers
and dedicated processing units has made
DSP more and more important in weak signal work.
Very powerful Multiple Channel Spectrum Analyzers and pattern recognition
engines are used in SETI. These instruments are all DSP-based.
An example of a Software Based MCA
that can be used for Amateur SETI, MS Meteor Scatter, Beacon Monitoring
and EME Carrier Detection.
For regular cw code detection the MCSA may not be optimal due to the
time requirements even for low speed cw ( 5 wpm ). For those tasks
a matched DSP Filter
can be more useful.
You are encouraged to participate in a Research Project on Receivers and
Noise by W8MQW
A well balanced approach to DSP and Moonbounce Communication could
be a MCSA for detecting the presence of weak Keyed Carriers in the IF
Passband. This information could then be used to fine-tune the
receiver, so that the Beatnote Frequency matches the Passband of
the Matched Filter.
The Antenna performs a vital function in coupling the Receiver,
Digital Signal Processor, Readout Device and Transmitter to the
Electro-Magnetic Universe and its frequency domain.
The design, construction and properties of an antenna, the noise
and gain characteristics as well as the coupling of the antenna
to the first modules in the detecting or other signal processing
equipment play a vital roll in the overall system performance
Reflectors (Dish Antennae) represent a Dominant Group among the
different types of Antenna Systems that are used in space communications.
Much Design, Engineering, Research and Science go into these Systems.
Many forms and structures have been tested, constructed and used
over the years and the development of newer systems remains ongoing .
Some Examples are presented here:
This antenna was located in Andover, Maine US. (This picture has been made available by Greg Wetzel from Bell Labs)
You can upload anonymously FTP to: nitehawk.com/pub/upload/rasmit/
You are invited to visit My Home Page.
While you are at it, you could check This Server to get info on Homepages.
For your Comments: W6/PA0ZN
Charter Member.