RF Noise and Radio-Astronomy

A Brief History of Radio Astronomy

1860's Maxwell develops equations that govern electromagnetic (EM) waves.

1860's-1930's physicists suspect celestial bodies to emit EM waves of non-visible wavelength.

1930's Karl Jansky discovered interference patterns in voice communications.

A Brief History of Radio Astronomy

1933 Through investigation and consultation he was able to track the source of interference to the center of our galaxy.

1933-present This discovery inspired other scientists and engineers to come together to design and build radio telescopes.

What is Radio Astronomy

The sub-category of the natural science Astronomy concerned with Radio Frequency emanation from celestial bodies.

Why is Radio Astronomy Important

A Paramount tool for: Discovery

Science

Curiosity

Explanation

Many important scientific discoveries have been proven by the use of radio astronomy.

The Big Bang

Cosmic microwave background radiation

New planets and galaxies

Radio galaxies, quasars, pulsars, masers

Listening and Broadcasting

“listening to space” The principle is simple. Implementation is not

Radio signals picked up by antennae are converted into audio signals.

These audio signals can be analyzed to tell us more about space.

How Radio Astronomy is Implemented

An “image” of radio space is acquired by scanning space with an antenna.

The antenna will pick up the emanations very similar to wireless communications.

The data that is read in is sorted by frequency and shifted to a visible wavelength.

How Radio Astronomy is Implemented

Scanning an area will give us an image of the area.

Astronomers require an extremely large signal to noise ratio to produce a valuable image or audio signal.

The Problem

The frequencies of interest to Radio Astronomers correspond to frequencies RF engineers use for communications.

The man-made radio emissions are intercepted by the radio astronomers.

This corrupts the astronomers data leading to inaccuracies in observations and interpretations.

A Contemporary Concern In January 2012 the World Radio-communication

Conference's topic was interfering with radio astronomy

The relationship between radio astronomer and RF engineer once a great partnership has now grown tense.

Allocation Frequencies that are chosen for allocation are

specially chosen for radio astronomy.

The frequencies allocated to radio astronomy: 608 – 614 MHz,

1406,

1420 – 1666 MHz,

23, 33, 41, 61, 94 GHz

Much is Already Lost

RF ranges have encroached deeply into the observable frequencies.

The 71-275 GHz portion of the radio spectrum is the portion that is in danger

Much of the 3-30 GHz range has already been lost to the widespread use of radar, satellite communications, and wireless telecommunications.

Communication Equipment

Examples of equipment that compete for radio astronomy:

UAS – unmanned aircraft services need 50MHz of useful spectrum

Satellite Down links – Iridium satellite system, GLONASS

Spectroscopy

Imaging

radar

Other communication devices (short distance, high power)

Communication Equipment

Spill over from communication is also a prominent problem

The equipment in place is designed to operate in it's allocated range.

The equipment “spills” over into the radio astronomy range.

Enforcement

There is no agreement on how this issue should be addressed

The regulatory groups are not sure if it should be dealt with by a universal regulatory body or a case by case basis.

There are regulatory measures in place to protect astronomers but they are rarely enforced.

The Problem Revisited

The spectral range that is used in radio astronomy is as of yet largely unexplored and somewhat unclaimed, but as technology progresses other uses for these frequencies are being discovered.

The RAS and EESS are becoming more and more concerned.

The Solution

There is no easy solution to this problem.

Radio astronomy is of paramount importance in contributing to our understanding of the universe.

Our expanding need for better communications requires more and more bandwidth.

Some temporary solutions have been implemented and are as follows.

Radio Interferometry

To combat the signal to noise ratio problem radio interferometry has been developed.

Interferometry is using arrays of antennas to produce multiple sets of data and filter out the noise.

The problem: a very expensive solution as many antennae are needed, and it is still subject to noise.

High Selectivity Antennae

This poor solution works on a very basic principle.

If we examine only a small portion of the sky we can eliminate much of the radio noise picked up.

The problem: we lose much of the important information as well.

Satellite Radio Astronomy

Best results in removing noise from the signal is to remove the antenna from the noise.

By putting the antenna in far orbit astronomers hope to eliminate all man made noise from the equation.

The problem: This is a very expensive solution. Space has become cluttered with communications satellites and “space garbage” leaving little room for radioastronomical satellites.

Stewardship

Conclusions Drawn:

There is no good solution as of now for protecting radio astronomy from communications equipment

We as engineers must act as stewards of science when designing communications equipment.

Questions