240
13 Range-Finding Radio Navigation Systems
this connection, the requirements to stability of reference oscillator in RRNS with
responder are considerably lower and have the following order.
δ f car
f car
= 10
−5
.
Such frequency stability is provided, for example, by the standard quartz (crystal)
oscillator. This represents the main advantage of RRNS with responder, thanks to
which they have widespread application nowadays.
The main disadvantages of RRNS are the following:
• limited bandwidth capacity (depending mainly on energy capabilities of
transmitter-responder, which should with a required quality operate with specified
amount of interrogators);
• RRNS operational range is limited by a power of onboard transmitter;
• lower interference immunity due to presence of two communication channels
comparing to RRNS without responder;
• operation of interrogation and respond channels (links) is usually carried out at
different frequencies that lead to expansion of occupied bandwidth.
On air transport, the RRNS are represented by DME system (distance-measuring
equipment), which in combination with AV onboard equipment is intended for
measuring of slant distance between AV and ground radio beacon. DME radio
beacons are installed at airfields and air routes of civil aviation.
The principle of range measurement is based on pulsed (temporal) method. The
information on range is within a time interval between a radiation moment of AV
onboard equipment of “range request” (RQ) signal and receiving moment of “range
response” (RS) signal from ground DME radio beacon. RQ and RS signals are
transmitted at different bandwidth using the differing from each other codes. This
technique permits to avoid initiation of DME transmitter (and formation of false
range responses) by signals of DME radio beacon, reflected from clutters, and to
reduce effect of neighboring radio beacons and increase interference immunity of
range channel.
Depending on signal format there could be DME/N and DME/P.
DME/N
1 —distance-measuring (ranging) equipment, primarily intended for operational navigational needs servicing en route or in terminal control area, where “N”
is narrow spectral characteristics.
DME/P
2 —ranging element of MLS landing system, where “P” means an precise
distance measuring. Spectral characteristics are similar to DME/N. DME/P has two
operational modes, IA and FA. Mode of final approach stage at landing (FA)—
DME/P operation conditions, which provide flights in final approaching zone and in
runaway area. Mode of initial approach stage at landing (IA)—DME/P operation
conditions, which provide flights beyond the final approaching zone and at which
1 Narrow band distance-measuring equipment.
2 Precision distance-measuring equipment.
13 Range-Finding Radio Navigation Systems
this connection, the requirements to stability of reference oscillator in RRNS with
responder are considerably lower and have the following order.
δ f car
f car
= 10
−5
.
Such frequency stability is provided, for example, by the standard quartz (crystal)
oscillator. This represents the main advantage of RRNS with responder, thanks to
which they have widespread application nowadays.
The main disadvantages of RRNS are the following:
• limited bandwidth capacity (depending mainly on energy capabilities of
transmitter-responder, which should with a required quality operate with specified
amount of interrogators);
• RRNS operational range is limited by a power of onboard transmitter;
• lower interference immunity due to presence of two communication channels
comparing to RRNS without responder;
• operation of interrogation and respond channels (links) is usually carried out at
different frequencies that lead to expansion of occupied bandwidth.
On air transport, the RRNS are represented by DME system (distance-measuring
equipment), which in combination with AV onboard equipment is intended for
measuring of slant distance between AV and ground radio beacon. DME radio
beacons are installed at airfields and air routes of civil aviation.
The principle of range measurement is based on pulsed (temporal) method. The
information on range is within a time interval between a radiation moment of AV
onboard equipment of “range request” (RQ) signal and receiving moment of “range
response” (RS) signal from ground DME radio beacon. RQ and RS signals are
transmitted at different bandwidth using the differing from each other codes. This
technique permits to avoid initiation of DME transmitter (and formation of false
range responses) by signals of DME radio beacon, reflected from clutters, and to
reduce effect of neighboring radio beacons and increase interference immunity of
range channel.
Depending on signal format there could be DME/N and DME/P.
DME/N
1 —distance-measuring (ranging) equipment, primarily intended for operational navigational needs servicing en route or in terminal control area, where “N”
is narrow spectral characteristics.
DME/P
2 —ranging element of MLS landing system, where “P” means an precise
distance measuring. Spectral characteristics are similar to DME/N. DME/P has two
operational modes, IA and FA. Mode of final approach stage at landing (FA)—
DME/P operation conditions, which provide flights in final approaching zone and in
runaway area. Mode of initial approach stage at landing (IA)—DME/P operation
conditions, which provide flights beyond the final approaching zone and at which
1 Narrow band distance-measuring equipment.
2 Precision distance-measuring equipment.