The VHF (Very High Frequency, 30 MHz to 300 MHz) and UHF (Ultra High Frequency, 300 MHz to 3 GHz) bands cover a wide range of frequencies used by official radio astronomy research.

At amateur level, in the VHF (metric waves) will be relatively simple the reception of the galactic center, Cassiopeia A and Cygnus A, and installing a good antenna system with a enough sensitive receiver, you can also reveal the most powerful pulsar, because their mechanism of emission, present a maximum emission precisely in the VHF band.

 

VHF-UHF experimental modular receiving station (132-136 MHz, 327 MHz, 408 MHz) for radio astronomy use.

VHF-UHF modular receiving station

 

In the picture are shown the three modules making up the electronics (the "internal" receiving station, positioned in remote local respect to the antenna system and thermostated to stability issues) of the VHF-UHF modular receiver.

This is an experimental station used by the author for several years in radio astronomy observations in the VHF and UHF bands.

The receiver is physically organized into 3 main screens canisters, along with a group of external containers that comprise the stages switchable high frequency and its powers. Each box includes its own stabilized power supply circuits, while the controls, displays and connections are arranged so as to be able to "dial" the system simply overlapping the various modules. Using this "philosophy" of construction was very easy to design, build and test the various modules that make up the receiver without having to "rethink" the entire system, taking advantage of the undeniable advantage of being able to optimize the operation of each part independently from that of the other.

Coupled to a suitable antenna system, the tool has been used for the study of the most important galactic radio sources, the Sun and the Pulsar.

The first thing you should to plan carefully before starting the observations is to verify the "cleaning" of the reception band in the area of installation for the radio telescope: any interference and disturbance, including those caused by local pulse due to ignition systems internal combustion engine (it is good practice to provide the greatest possible distance from the busy streets), would make very difficult the reception of weak signals cosmic defeating all constructive efforts.

The best thing, to ascertain with certainty the degree of "pollution radio" in the spectral band for the observations, is to monitor the range with a suitable receiver (better still using a spectrum analyzer or a scanner) equipped with antenna sufficiently directive during the 24 hours daily and for a long time.
In this way it will be possible to establish also the direction of provenance of the main radio-interference of the various disorders and, in addition to their nature and the specific banda employment.

 

Radio observation of meteor tracks by radio-echo Doppler in VHF

Whenever a meteor passes through the upper atmosphere produces a column of ionized air tens of kilometers long, with a ranging height between 85 km and 105 km. This ionized medium is able to reflect radio waves generated by the transmitters placed on the surface of the Earth. It's occurs a phenomenon of reflection with similar characteristics to those experimented by the light that influence on a mirror surface: this reflections are short-lived due to the gradual dissolution of the ionized track (ion diffusion into the surrounding air). The ability to reflect radio waves occurs, then, for generally less than 1 second durations, even if, occasionally, large meteors can trigger ionized tracks able to reflect radio waves for several minutes.

If the radio waves generated by the transmitter on the ground "illuminate" the meteor along a perpendicular path, the reflected signal will be directed towards the transmitter (back-scatter) and can be analyzed: this is one of the most common methods through radio waves , with which astronomers studying the meteors, since each meteor will produce a specific "radio-echo" according to its mass, velocity, angle and direction of entry into the atmosphere, as well as a function of distance from the transmitter. Research of this type are currently made using the powerful radio telescope of Arecibo (Puerto Rico), very suitable for the study of extremely small meteoric events.

If the beam of the radio transmitter affects ionized track with an angle other than perpendicular, the reflected signal will be projected forward on the ground at a certain distance from the transmitter. This mode is called forward-scatter, and the area on the ground where it is reflected signal is called scatter-footprint, footprint very close and several kilometers long. The most common meteoric traces are able to reflect radio signals over distances varying between 300 km and 1500 km. The most important advantage of the method forward-scatter is that you can use the signals from radio transmitters for different purposes, such as for commercial broadcasting, very powerful and located anywhere, leaving the researcher with the construction of the receiving station, which specializes in the requirements of the measurement. The disadvantage of this research method is that the geometry is much more complex than back-scatter, making more difficult the determination of the meteoric parameters.

The analysis of radio-echoes of commercial radio transmitters is definitely within the reach of the amateur radio astronomer.

 

Meteor scatter

 

Useful information about this interesting research project can be found at:

http://www.amsmeteors.org/ams-programs/radio-observing/