CLIAMS:1.- A radio altimetry system that can be fixed to an aircraft and provide the distance of that aircraft from a surface, capable of operating in a dual radio altimetry installation (2) including two such radio altimetry systems, said radio altimetry system including a frequency-modulated radio wave generator using a modulation signal including frequency variation ramps according to a frequency swing defined by at least one parameter,
characterized in that it includes means (26) for obtaining an identifier making it possible to distinguish said radio altimetry system from the other radio altimetry system of said dual installation (2),
and means (30) for selecting said at least one parameter defining the frequency swing of the modulation signal as a function of the obtained identifier.

2.- The radio altimetry system according to claim 1, characterized in that the frequency swing is defined by a predetermined frequency variation value ΔF and by an associated positive or negative variation direction, and said parameter defines said variation direction.

3.- The radio altimetry system according to one of the preceding claims, characterized in that the identifier is a number having a value from among two possible values.

4.- The radio altimetry system according to one of the preceding claims, characterized in that it further includes means (42, 44) for receiving radio waves, means (48) for subtracting the transmitted radio wave and the received radio wave to form a beat signal and means (52) for filtering said beat signal.

5.- The radio altimetry system according to claim 4, characterized in that said filtering means are capable of filtering said beat signal in a predetermined frequency band.

6.- The radio altimetry system according to one of the preceding claims, characterized in that the means (26) for obtaining the identifier include means for reading an identifier introduced by an operator using a suitable interface (28).

7.- A radio altimetry installation (2) including two radio altimetry systems according to one of claims 1 to 6. ,TagSPECI:As Attached