RADIO ASTRONOMY EQUIPMENT

My radio astronomy equipment comprises five stand-alone telescopes, as follows:

1. Solar Observation Scope using a large satellite TV antenna, centre frequency 12 GHz - for observation of sunspot activity.

2. Milky Way Observation Scope, using a 1m parabolic mesh antenna, centre frequency 1.42 GHz - for observation of hydrogen clouds in the Milky Way galactic arms.

3. Meteor Detection Scope, using a folded dipole antenna modified with a parasitic back-reflector, centre frequency  50.408 MHz - for observation of meteor activity utilising the British Astronomical Association GB3MBA radio beacon.

4. Sudden Ionospheric Disturbance (SID) Detector, using an L-shaped antenna with an electrical length of 7 ft (horiz) x 14.3 ft (vert).

5. Aurora Detector, employing a remote electric field antenna and local magnetic field antenna to give a combined audio output.

SOLAR OBSERVATION

The surface of the Sun that we observe in the visible is called the photosphere. But the lower region of the Sun's atmosphere is called the chromosphere and, together with the corona, is where most of its radio emissions arise. 

The thermal component of solar radiation follows the black body law and is predominant at high frequencies (Infrared, f> 300 GHz & also some high-end radio waves, f> 3 GHz), while the non-thermal component (synchrotron radiation) is predominant at lower frequencies (microwave, f <3 GHz).

Note: Infrared spectrum is 300 GHz to 400 THz. 

My telescope is picking up mainly synchrotron radiation, produced by charged particles being accelerated by the sun’s magnetic field.

An active Sun has much larger flux density than does a quiet Sun in the frequency range between 100 MHz (3-m wavelength) and 30 GHz (1 cm wavelength). So the telescope is ideal for picking up flare activity.

Synchrotron radiation occurs when a moving, charged particle is accelerated by magnetic field lines in a direction perpendicular to its movement, i.e., outwards from the sun. 

NOTE: the condition for the production of an EM wave is acceleration of charged particles.

GALACTIC HYDROGEN OBSERVATION

There are three forms of hydrogen that exist in our galaxy:

(1) HI – neutral hydrogen. This naturally radiates electromagnetic radiation at  1.420405752 GHz (21 cm wavelength), due to a phenomenon known as electron spin-flip. The signal is very weak and sits amidst the general 'noise', but my radio telescope is able to detect that peak by employing spectrum averaging software, which elevates the wanted signal sufficiently above the noise floor for detection. 

(2) HII - ionised hydrogen.  Atoms of this form of hydrogen comprise single protons whose electrons have been removed during high-temperature events in space. When hydrogen is ionised, a soup of free electrons and free protons is created. Hence, as these particles are charged, they generate electromagnetic radiation when they accelerate, collectively producing a strong, smooth continuum of frequencies.

(3) H2 – molecular hydrogen.  This is radio-silent but its presence can be inferred by observing the behaviour of the cold HI envelope that always surrounds it. 

For more in-depth details of hydrogen detection physics and the techniques I use, please follow this link: DETAILED EXPLANATION  

At a basic level, what is interesting is that the peak signal frequency of the HI will vary depending upon whereabouts the telescope is aimed within the galaxy. This is due to the fact that different parts of the galaxy are moving at different relative velocities to us on Earth (due to the galactic rotation and other localised phenomena), and so this causes the radiated frequency to be modified by the Doppler Effect.

This radial velocity (velocity along the line of sight of the telescope) can actually be calculated by noting the observed frequency of the peak measured by the telescope and applying a calculation.

Using this technique, I can plot a radial velocity map of the observed parts of the Milky Way and, from any large velocity changes, distinguish between different galactic arms. 

The arms of the Milky Way are shown below: 

METEOR DETECTION

I detect meteors using a radio signal transmitted from a beacon located near Nottingham. See:  Meteor Beacon

The signal is a 50.408MHz (CW) signal, transmitted vertically upwards into a region 80 to 100km up in the atmosphere. 

Any  meteors entering the earth's atmosphere here interact with the beacon signal.

This telescope can also be used for the detection of aurora activity and transient phenomena, such as the lower frequencies of radiation associated with gamma ray bursts.  

AURORA DETECTION

My ELF/VLF aurora detector is sensitive between 300 Hz and 10 kHz and comprises two parallel channels:

(1) An electric field detector fitted with a short copper rod antenna.

(2) A magnetic field detector using a wire-wound ferrite rod antenna.

The copper rod antenna is remote from the observatory to minimise the effect of local electrical interference. The magnetic ferrite rod antenna is mounted in the observatory, suitably distanced from mains cables. Both antennae feed amplifier circuits whose outputs are then fed to a final audio stage, which drives two small loudspeakers, allowing me to 'listen' to the earth's atmosphere for auroral activity!

The sun is always emitting solar wind, a stream of charged particles that interact with the earth’s magnetic field, mostly to be deflected into space. However, when there is a strong surge of the charged particles, such as after a solar CME, a significant number of them get funnelled down towards the poles along the flux lines of the magnetic field.

Whenever this happens, a luminous aurora is generated due to the charged particles colliding with nitrogen and oxygen molecules in our atmosphere. But that is not the only effect. As a stream of charged particles is moving through a magnetic field, RF electromagnetic radiation is also produced, with strong components between 1–10 kHz

At ELF and VLF, the earth and its ionosphere collectively behave like a giant waveguide of approximately 90 km width, trapping the electromagnetic energy generated between the the conducting Earth below and the ionosphere above. The electric fields generated bounce, duct, and reinforce over enormous distances, which produces surprisingly strong electric fields.

At the ground itself, the tangential electric field must of course be zero, so the electric field lines will be pretty much vertical near the surface. And vertical fields couple extremely well to a short rod antenna, because the rod acts as a vertical capacitor plate. Electrons in it are pulled one way leaving a positive charge (the deficit of electrons) on the opposite side. And as the field alternates, the charge on the rod oscillates making a tiny current flow into and out of the rod.

The antenna is connected directly to a pre-amp, which converts this current into a measurable voltage that drives the audio amplifier and loudspeaker stage.

Meanwhile, the wire-wound ferrite rod antenna of the second, magnetic channel couples with the magnetic element of the generated electromagnetic waves, and similarly drives a pre-amp and outputs to the audio stage. So the result is a combined audible output.

When the atmosphere is quiet, I pick up a clean, thin atmospheric hiss punctuated by the occasional crackles of distant 'sferics'. But when an aurora occurs, the hiss becomes thick and restless and is modulated by surges in signal level.

I should add that these pictures were taken before I fitted transient (e.g., lighning induced) protection to the E-field antenna (comprising good earthing via a gas discharge tube). Very necessary!!