15.1 Radio Beacon Goniometric Radio Navigation Systems
289
To get reference voltages, the pulses from decoder output are amplified and
limited in amplifier-limiter. Pulses of constant amplitude come to decoding cascades.
Decoding cascade of rough signal (DC r ) extracts from chaotic sequence of pulses the
signals, corresponding to groups of 12 pulses, following with interval of 30 μs. These
signals are converted into reference voltage of 15 Hz. Decoding cascade of precise
signal (DC p ) extracts pulsed sequences, consisting of six elements with interval of
24 μs, and forms a frequency reference voltage of 135 Hz. Reference voltages of 15
and 135 frequencies come to phase detectors of rough (PDC r ) and precise (PDC p )
channels, correspondingly.
Voltage is produced in channel of variable phase, presenting signals amplitude
modulation law of radio beacon. Envelope extracting is carried out by peak detector.
Detector output voltage is delivered to filters of rough (F r ) and precise (F p ) channels,
which extract frequency oscillations of 15 and 135 Hz, correspondingly.
Onboard equipment includes two automatic follow-up (servo) phase meters, one
of which operates at 15 Hz frequency and is intended for multiple-valuedness elimination, another one—at 135 Hz frequency and is intended for precise measuring of
azimuth. Phase meter operation principle is analogue to a phase meter, examined at
an example of VOR system meter. Corresponding rotors of phase shifters of precise
(PS p ) and rough (PS r ) channels are connected between each other mechanically
through gearbox with 9:1 transmission ratio (GB 9:1).
In “Search” mode, an engine (Eng) rotates phase shifters rotors till the moment
of azimuth measuring in rough channel. For measuring in channel, a pulse gate
±20° of 15 Hz with phase, depending on AV azimuth, is shaped in channel. Pulse
gate comes to input of phase detector (PD r ). After rough measuring of azimuth,
the system switches to “Tracking” mode. In this mode an output voltage of phase
detector (PD p ) via closed-loop switching unit K comes C to converter. Engine rotates
till the moment of voltage outage from PD p output, i.e., till the moment of azimuth
measuring in precise channel.
Hence, an angular position of phase shifters rotors corresponds to azimuth value.
Azimuth value is transmitted to indicator via synchro pickup (SyP).
Bandwidth, used in PVOR, ranges from 962…1213 MHz. As compared to VOR,
the two-step azimuth measuring system has a higher accuracy (0, 75…1°), relatively
small sizes and weight. Application of two-step method stipulates the use of special
onboard equipment. Two-step azimuth determination method is realized in tactical
air navigation system (TACAN) system.
In PVOR radio beacons the special mode of call signal sending is stipulated.
At sending of call signals the transmitter generates signals with constant repetition
rate of 2700 Hz. Herewith, at output of receiving unit, the tone alternating voltage
of 2700 Hz is produced. By manipulating of these signals transmission time, it is
possible to transmit signals via the Morse code.
To increase azimuth measurement accuracy by VOR onboard equipment the radio
beacons were developed, the operation principle of which is based on use of Doppler
effect.
DVOR system (Doppler VOR). DVOR RB antenna system consists of central
and side antennas (Fig. 15.10). The central antenna A cnt is located in the origin of
289
To get reference voltages, the pulses from decoder output are amplified and
limited in amplifier-limiter. Pulses of constant amplitude come to decoding cascades.
Decoding cascade of rough signal (DC r ) extracts from chaotic sequence of pulses the
signals, corresponding to groups of 12 pulses, following with interval of 30 μs. These
signals are converted into reference voltage of 15 Hz. Decoding cascade of precise
signal (DC p ) extracts pulsed sequences, consisting of six elements with interval of
24 μs, and forms a frequency reference voltage of 135 Hz. Reference voltages of 15
and 135 frequencies come to phase detectors of rough (PDC r ) and precise (PDC p )
channels, correspondingly.
Voltage is produced in channel of variable phase, presenting signals amplitude
modulation law of radio beacon. Envelope extracting is carried out by peak detector.
Detector output voltage is delivered to filters of rough (F r ) and precise (F p ) channels,
which extract frequency oscillations of 15 and 135 Hz, correspondingly.
Onboard equipment includes two automatic follow-up (servo) phase meters, one
of which operates at 15 Hz frequency and is intended for multiple-valuedness elimination, another one—at 135 Hz frequency and is intended for precise measuring of
azimuth. Phase meter operation principle is analogue to a phase meter, examined at
an example of VOR system meter. Corresponding rotors of phase shifters of precise
(PS p ) and rough (PS r ) channels are connected between each other mechanically
through gearbox with 9:1 transmission ratio (GB 9:1).
In “Search” mode, an engine (Eng) rotates phase shifters rotors till the moment
of azimuth measuring in rough channel. For measuring in channel, a pulse gate
±20° of 15 Hz with phase, depending on AV azimuth, is shaped in channel. Pulse
gate comes to input of phase detector (PD r ). After rough measuring of azimuth,
the system switches to “Tracking” mode. In this mode an output voltage of phase
detector (PD p ) via closed-loop switching unit K comes C to converter. Engine rotates
till the moment of voltage outage from PD p output, i.e., till the moment of azimuth
measuring in precise channel.
Hence, an angular position of phase shifters rotors corresponds to azimuth value.
Azimuth value is transmitted to indicator via synchro pickup (SyP).
Bandwidth, used in PVOR, ranges from 962…1213 MHz. As compared to VOR,
the two-step azimuth measuring system has a higher accuracy (0, 75…1°), relatively
small sizes and weight. Application of two-step method stipulates the use of special
onboard equipment. Two-step azimuth determination method is realized in tactical
air navigation system (TACAN) system.
In PVOR radio beacons the special mode of call signal sending is stipulated.
At sending of call signals the transmitter generates signals with constant repetition
rate of 2700 Hz. Herewith, at output of receiving unit, the tone alternating voltage
of 2700 Hz is produced. By manipulating of these signals transmission time, it is
possible to transmit signals via the Morse code.
To increase azimuth measurement accuracy by VOR onboard equipment the radio
beacons were developed, the operation principle of which is based on use of Doppler
effect.
DVOR system (Doppler VOR). DVOR RB antenna system consists of central
and side antennas (Fig. 15.10). The central antenna A cnt is located in the origin of