Method

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The selection of a suitable transmitter, or transmitters, is crucial to the successful operation of a meteor detection system. For simplicity I opted to use existing high powered broadcast transmitters to provide my target signal. The advantages of using broadcast stations include the following:

The transmitter will usually operate with a high radiated power.
All transmitters will operate from fixed locations.
The transmitter will be operated with high reliability.
The broadcast bands are strictly regulated and the likelihood of interference from an unlicensed ‘pirate’ station, on the broadcaster’s frequency, is small.
There is no cost associated with providing the transmission.

The disadvantages of using a broadcast station include the following:

The broadcast bands are relatively congested and finding a suitable frequency, free of local transmissions, may be difficult.
Not all broadcast stations provide a 24-hour a day service.
The frequency bands allocated to broadcast stations may not coincide with the ideal frequency for meteor detection.
Not all types of broadcast signal provide a constant radiated power. For example, amplitude modulated signals may not be suitable without special consideration.

Finding a suitable frequency

To detect meteors by a radio forward scatter method we require a channel which is not used by any local transmitters, but which is used by one, or more, distant transmitter. The channel should appear unoccupied to a casual observer, yet the distant station must be of sufficient power that the signal reflected off of a meteor trail will be sufficiently strong to allow detection.

 The obvious choice of frequency is either the VHF Band II FM radio broadcasts, or the sound, or vision carrier from a VHF Band I TV transmission used in some European countries.  I opted to use the vision carrier from a European television transmitter in Portugal.