 |
|
From Mirrorbow Technologies Ltd |
|||
|---|---|---|---|
 |
|||
| PlaneGadget Radar | About ADS-B | Applications Information | FAQ | Terms and Conditions | Downloads |
PlaneGadget Radar - Applications Information
Quick Links:
Antenna Positioning
Using a different antenna or extending the coaxial lead
The antenna has a magnetic base and is intended for placing on a metallic surface. An increase in performance is obtained by doing this, and typically this is achieved by simply placing the antenna in the centre of an upturned biscuit tin or biscuit tin lid. Any flat metallic surface which the magnetic base can adhere to is suitable.
The antenna is not weather proof and should not be placed outside. With the exception of temporary attended operation, for example on a car body (place something under the antenna to avoid scratching your car paintwork if you do this, like thin polythene).
As ADS-B transmissions are what is known as "line of sight" you need to place the antenna in a suitable position where it has a clear view of the sky. An upstairs window sill for example is a typical convenient position, where the view directly out of the window is clear of obstacles such as hills or adjacent buildings. However in this position you will see a clear pattern where aircraft on the other side of your house are either not seen or where the range of detection is lower.
The following picture shows PlanePlotter* with the receiving antenna is placed in a 1st floor window facing south east from Oxford. You can clearly see that range is up to 110miles or so in that direction, but limited to around 30Nm in the north west. The north west is blocked by being the other side of the building from the antenna, several walls of the building and the roof.
Of course the situation in the above picture is exaggerated by the fact that there are many more aircraft to the south east due to the proximity of Heathrow.
You will also notice that the more distant aircraft tend to be higher, because the further out the aircraft is, the more likely the curvature of the earth or a local hill, or the houses across from your position will block the signal.
Dropping the antenna from the 1st floor window to ground floor in the above example loses about half of the aircraft as they become blocked behind local buildings and high ground.
You may also find that small changes in antenna position make a big difference to the aircraft picked up. For example, with the metal surround of double glazing in a window it can shield aircraft at certain angles, and reduce the range at which they are first detected.
Clearly the best place for the antenna is on top of a hill with no surrounding obstacles! But in practice perfectly satisfactory results are achieved on a simple 1st floor window sill in most cases.
Using a different antenna or extending the coaxial lead
The receiver comes with factory preset gain to the optimum settings for the antenna provided. For most uses this antenna is perfectly adequate, and it is position thats most important.
We would not recommend using a different antenna for this product. In some cases using a larger antenna can result in a much worse performance than using the antenna supplied.
Rather than extending the coaxial lead we would recommend using a longer USB cable and perhaps USB hubs to extend the distance. This will minimise the losses of the more sensitive ADS-B signals.
NOTE: Whip antennas have a beam shape that is like a donut (imagine a donut laying flat with the antenna vertical in the middle). This means that there is a dead area on top of the antenna as it is vertically polarised. Often higher gain whip antennas have a more pronounced dip. Since the aircraft also has a vertically polarised antenna, when they fly directly overhead the signal can get substantially weaker, as both antennas are effectively pointing their tips at each other. This may cause aircraft to be lost when they are directly overhead, especially if you were tracking an aircraft through the roof material of your house for example which would already have attenuated the signal. It's counter intuitive that you might have more trouble picking up an aircraft overhead than 100 miles out, however with whip antennas the maximum gain is sideways, so the efficiency of the antenna close over head is much less than side on. You could find for example that aircraft over a few thousand feet within 2 miles become more difficult to detect.
*PlanePlotterLite is supplied by COAA an independent company separate from RadarGadgets and Mirrorbow Technologies Ltd.