The two satellites being built by students of the Cape Peninsula University of Technology (CPUT) include a beacon operating in the 20 m amateur band. The first of the two is a single CubeSat 10 x 10 x 10 cm with a mass of one kilogramme.

While the single CubeSat will be dedicated to the Hermanus Magnetic Observatory science payload supporting the HMO operations in Antarctica, it will provide interesting antenna characterisation opportunities for radio amateurs.

The beacon operating on 14 099 kHz will be used for optimising the SuperDarn HF radar system operated by the National Space Agency Space Science (previously the Hermanus Magnetic observatory).

The electrically conductive upper layer of the Earth’s atmosphere (known as the ionosphere) sometimes connect directly to the solar wind. If there is a strong coupling then there is an increased chance that the space environment immediately surrounding our planet will be disrupted – the fast-moving solar wind blowing past the Earth can drag the polar ionosphere with it. Scientists use the SuperDARN radar system to measure how the ionosphere is moving above the polar cap by detecting echoes reflected by patches of electrically charged particles.

In our increasingly high-tech society, space research is becoming an important research area because some modern technologies, both in space and on the ground, are vulnerable to rapid changes in the space environment known as “space weather”.

Why satellite signals?

As with all radio systems phase characteristics change with time. The phase path through the system needs to be calibrated on a regular basis and this can be achieved by introducing another signal into the system and then measure the phase coming out.

As the CubeSat passes over the Antarctic it will be in full view of the radar antennas. Scientists will then measure the signal and determine what the phase difference is.

Ean Retief ZS1PR, a Cape Town radio amateur with a special interest in radio propagation, suggested that the signal be used for determining the coverage (beam) pattern of 20 m antennas. Currently obtaining a reasonable coverage pattern for an antenna takes a long time as testing with other radio amateurs introduces a number of variables such as variation in ionospheric propagation conditions (day to day, seasonal, time of the day and the stage of the sunspot cycle), different power levels of the distant stations and different antennas being used by the distant stations.

The CubeSat HF beacon will be a known unchanging (same output and same antenna) source and with a known flight path the angle and range of the cube-sat will be known for the entire traverse. Therefore the observer simply needs to note time and received signal strength every few moments.

A “lobe pattern” can be drawn for the particular path followed by the CubeSat during a pass. With three to six passes available daily a rough estimate of the antenna pattern can be estimated after only one day of monitoring.

After a week of observation it should be possible to draw quite a good “in situ” coverage pattern, as not only will the lobes of the antenna be recorded but also any local screening effects of mountains, hills and nearby buildings.

If the antenna is then modified in any way, the effects of such modifications will be easily detectable after observing a few passes.

Propagation research

The beacon signal can also be used for the study of various modes of propagation. Questions such as “how does an HF signal above the ionosphere behave during various times of the day and sunspot cycle” can be answered. Will it penetrate through the ionosphere as the layers change or will it travel along the upper layer before penetrating?

As monitoring of the CubeSat signal will only require a receiver with a “S” meter and an accurate clock, the possibility also exists for constructing simple antenna configurations at youth camps or schools. By re-orienting the antenna in direction or configuration (i.e. “straight” dipole versus “inverted-V”) the effect should be noticeable during the next pass of the CubeSat and will give quick “hands on” learning. Varying the height above ground will also show the change in pattern.

The beacon signal can also be used to demonstrate the different effects of different antennas. For instance it will show the difference in signal strength during different parts of a satellite pass between different antennas (i.e. dipole giving better results at higher elevation while vertical gives better result at lower elevation). Coupled with modern antenna modelling software it will give participants the “proof of the pudding” of what they saw on a computer screen.

A simple satellite beacon can be used for so many interesting experiments and activities and add new interest to amateur radio.

http://www.amsatsa.org.za/