Difference between revisions of "Antennas"
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==Rotator Ground Station==
==Rotator Ground Station==
Revision as of 20:35, 10 January 2018
The type of antenna largely depends on the type of ground station. A no rotator ground station will benefit from a different type of antenna to a rotator based ground station. The two different approaches are explored below. In addition to the choice of antenna the choice of location for the ground station will have an effect on the quality of observations.
Non-Rotator Ground Station
This type of ground station will require an antenna that will give a broad coverage from its fixed position. It is therefore not just the antenna that needs to be considered but also the proximity of buildings, geography or metallic structures that might be in the path of a line of sight between the ground station and satellite.
Typical ground stations have had success with simple wire antennas that can be commercially bought or made at home. Colinear or ‘white stick’ antennas are vertically polarised omnidirectional antennas. These have anecdotally been used for successful satellite work but should be avoided. The following are considered suitable choices:
Rotator Ground Station
A rotator based ground station is able to make use of directional antennas. These will have a directional gain, meaning that you will need to point them in the direction of the satellite but the signal you receive will be stronger and for longer. They will allow much lower to the horizon passes to be received and more successful observations. These are not complex antennas but the choice will depend on the type of satellite and there are variations on the main types. Yagi, helical and quad.
- Yagi antennas. – A common type of antenna that is either horizontally or vertically polarised. Simple to construct and suitable for a large number of satellites. Designs for the SatNOGS versions for VHF and UHF are here here.
- Helical antennas – A less common type that are ‘handed’. The antenna looks a bit like a corkscrew and can be either LHCP (Left hand circular polarisation) or RHCP (right hand circular polarisation). The SatNOGS designs are here.
- Quad antennas – This type of antenna has a square appearance and have electrically switchable polarisation, some types will be horizontal, vertical or circularly polarised. No SatNOGS designs currently exist for this type of antenna.
For reference the NEC files for modelling of the antennas is also available from The Git Repository.
Constructing the SatNOGS antennas
Guides are available for construction the SatNOGS designs. The Yagi antennas are simpler and require no specialist tools whilst the helical antenna will need access to milling and turning equipment.
- Yagi construction guide (Construction guide required)
- UHF helical antenna construction guide – V5 Design
An alternative to home made antennas is to buy a commercial type. These can be expensive and will, in general, not offer significant improvements over well constructed homebrew antenna. Bothe the Arrow Arrow II Satellite Antenna and Elk antennas Log Periodic are commonly used for ground stations as well as the Wimo X Quad Antenna's