In order to allow multiple users at a flying site at one time, some form of frequency control must be rigorously enforced to avoid users unintentionally shooting down someone else's aircraft.
The two primary methods, both based around a board with one space for each channel.
Take a peg
- Each channel is represented by a numbered peg; the flyer must acquire the peg for their channel before flying. The primary drawback of this method is that users sometimes forget to return the peg at the end of their session. Eventually a new peg will be produced to replace the old one; unfortunately there are then two pegs in existence for that frequency, and if the original one turns up, two users could try to use the same channel at once.
Leave a peg
- Each channel is represented by a numbered space, in which a user should leave something relatively valuable and personally identifying that they are very unlikely to leave the field without – car keys are sometimes suggested. As there are no pegs, they cannot be lost, but items can easily be accidentally or deliberately removed from the board, making it appear that the channel is clear. Obviously it is also easy to steal the item.
The two methods can be combined, so that the user takes a peg and leaves an item; this reduces the possibility that the peg is not returned to the board and helps to identify the culprit should it occur, and also ensures that the lack of any item does not indicate a free channel. The security problem remains.
One of the major advantages of 2,4GHz radio gear is that it must be designed to be tolerant of and avoid creating undue interference, and thus requires much less rigorous frequency control – usually all that should be required is a limit to the number of simultaneous users to some unfeasibly large number (about 50). The methods used include rapid frequency hopping (Futaba's FASST) or automatically finding two unused channels, and broadcasting on both simultaneously (Spektrum's DSM).
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