Outdoor Radio Testing
Author: Levente Buzas
On March 10th the first TT&C outdoor test was completed. The objective of this test is to demonstrate the ability of all components of the TT&C subsystem to work together as a complete end to end satellite communication system for ORCASat, and evaluate the performance of the ORCASat antenna compared to a simple half wavelength dipole.
Mt. Douglas and Mt. Tolmie were chosen as locations for the space station and ground station radios. These were chosen because of the direct line of sight between the locations. The ground station used a small portable directional antenna mounted on a tripod, while the space station used the ORCASat antenna mounted on a fiberglass pole inside a prototype of the satellite.
First, a bi-directional half duplex radio link was successfully established between the two sites. Communication involved sending textual messages and various commands over the air. First, the attenuation presented by the free space path loss of the link had to be overcome. This was followed by adding external attenuation to the link, to the point where communication was no longer feasible. Both of these were successfully completed.
The performance of the ORCASat antenna was evaluated using a test based around comparing its performance to a simple half wavelength wire dipole. The basis of comparison was selected as the eye diagram, a graphical, time domain representation of signal quality. First, it was determined what amount of external attenuation needed to be added to the link to have the eye "close" (see photos below) for the main lobe of the dipole pointed at the "ground station". Then, this was also established for ~50 degrees (~0dBi gain) and 90 degrees (null) rotation of the dipole antenna. After that, the test antenna was replaced with the ORCASat one, and the test was repeated, allowing a comparison of the link performance between the two devices. It was found that the ORCASat antenna performed the same or marginally better than the reference, so the test was deemed successful.
