EME, SETI, Radio Astronomy and Radio Amateurs.

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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.

Dish Antenna.

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:

Antenna and Tracking.

Feed systems.

Preamplifier.

Connection to and Input of Receiver.

Characteristics of Receiver.

The Operator's ability to Copy weak Morse Code in Noise.

Planning for and Tracking of the Moon.

Generation of Power and Coupling to the Antenna.

Frequency Stability of the System.

The Desire to go out and collect "Items" for the System.

Knowledge of Radio, Computers and newer developments such as DSP.

The ability to test and maintain the system.

A friendly Neighbourhood and at least some Land around the Residence.

For Amateurs in a Relationship, an understanding Partner!

To appreciate, hearing one's own Echo's returning from Outerspace.

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.