Beijing Redyas Science & Technology Development Co.,Ltd
DOPPLER-VHF OMNI-DIRECTIONAL RADIO RANGE DVOR-RYS
SHORT DESCRIPTION
AND PERFORMANCE SPECIFICATION
Address: No. 2106, Tower A, New Ocean Express, Chaoyang Distr District, ict, Beijing, China (P.C.: 100027) Tel: +86-10- 64704300 Fax: +86-10-64704727 +86-10-64704727 E-mail:
[email protected]
Beijing Redyas Science & Technology Development Development Co.,Ltd
1. DVOR-RYS General Information
1 1 General
The VOR (Very high frequency Omnidirectional Radio range) is a radio navigation aid recommended by the ICAO and introduced internationally for short and medium range aircraft guidance. It can be remote controlled and remote monitored. The DVOR radio navigation equipment is a further development of the conventional VOR. Through its utilization of the Doppler Effect and a wide− based antenna system it is able to produce a considerably more precise azimuth signal. DVOR radio navigation installations installati ons are used mainly where the geographical conditions are difficult. The principle on which the (D) VOR operates is based on the measurement of the phase angle of two 30 Hz signals radiated by the station. One signal (reference signal) is radiated with the same phase in all directions. For the second 30Hz signal (variable signal), the phase relationship relative to the first signal changes as a function of the azimuth. The electric phase angle measured in the airborne receiver corresponds to the azimuth angle. Main features of DVOR-RYS in particular are as follows: ----Available as main or standby equipment with power up to 50W or 100W; ----advanced technology based on the established and proved Navaids System, in conformance with ICAO standards; ----Antenna configuration: 48 sideband antennas with DSB radiation, having a minimum of distortion on the 9960 Hz subcarrier, High signal quality and long time stability of transmitted signals, real time monitoring; ----30Hz ref phase are generated and controlled by micro-professor to act amplitude modulation . The phase number is adjustable. ----Carrier and sideband signal are generated by frequency synthesizer. The carrier frequency are changeable via keyboard, the phase number of the sideband signal are adjustable. ----Modular design, signal digitalization and unit modular design, features with high integrity and high reliability. ----Utilize LCD and keyboard, friendly interface and convenient to operate. ----Local computer can realize function of parameter setting, system calibration and status -1-
Beijing Redyas Science & Technology Development Development Co.,Ltd
indication through “LOCAL” port. ----Remote computer can realize function of parameter setting, system calibration and status indication through “REMOTE” port. ----Parameter can be set and modified by means of password. The DVOR system can be combined with a DME (Distance Measuring Equipment) to form a DVOR/ DME station. Then an aircraft can determine its position by referring to the location of a single DVOR/DME station. The DVOR equipment can be supplied already installed in a container shelter. The DVOR-antenna system is mounted on a counterpoise optionally available in different heights as made necessary depending by local conditions. 1.2 DVOR/VOR PRINCIPLE Todays airway network is marked by a number of VOR and DVOR ground beacons operating in the 108...118 MHz frequency range and having a transmission range of up to 300 km (optical propagation characteristics of VHF). VOR/DVOR produces an azimuth information which enables the pilot of an aircraft to fly from one (D)VOR station to another on a preselected course. Deviations from this course are indicated by an instrument giving the information "fly to the right" or "fly to the left" and also a "to/from" indication showing whether the aircraft is flying toward the beacon or away from it. The basic arrangement of a DVOR installation is shown in Fig. 1−1.
1.2.1 VOR Method The RF signal radiated by a VOR is modulated by two 30 Hz sinewaves. Both 30 Hz signals have a certain phase relationship, which is dependent on the direction from which the signal is received. The phase relationship is identical to the geographical angle between North and the -2-
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direction of the aircraft relative to the ground beacon (azimuth). One of the two 30 Hz oscillations is irrespective of the azimuth (reference signal), whilst the phase relationship of the second 30 Hz oscillation to the reference signal varies with the azimuth (variable signal). The reference signal and the variable signal are modulated in different ways. The direction-independent (reference) signal frequency modulates a subcarrier of f0 ±9960 Hz with a frequency shift of ±480 Hz. The subcarrier is then radiated as amplitude modulation of the carrier f 0 with 30% modulation depth by a horizontally polarised antenna with omni-directional characteristics. In addition, the carrier f 0 is modulated with an identity code (1020 Hz) as well as with voice(300~3000 Hz). The direction-dependent (variable) signal is radiated by 2 crossed dipoles. The crossed dipoles receive sideband signals from the two sideband transmitters with a 90° phase difference in the envelope. The carrier of the sideband signals is suppressed. This results in a signal-in-space with a "figure-eight pattern" rotating 30 times per second. Since the carrier f 0 is radiated by an antenna with omnidirectional characteristics, the superposition of the carrier and the 30Hz sidebands in the field - if the phase is correctly set-produces a pure amplitude modulation, with the phase of the resulting 30Hz signal being dependent on the azimuth, related to the 30Hz reference signal. 1.2.2 DVOR Method In the DVOR the functions of the two 30Hz oscillations have been interchanged as compared with the conventional VOR. This means that the 30Hz oscillation which amplitude-modulates the VHF carrier now acts as the reference signal, whilst the directional, frequency-modulated 30Hz oscillation (variable signal) is contained in the 9960Hz subcarrier. The carrier oscillation is transmitted omnidirectionally by a stationary center antenna. It is amplitude-modulated with the voice (300~3000Hz) and the identity code in addition to the 30Hz reference signal. The 9960Hz subcarrier signal is transmitted by a sideband radiator, which can be considered to be rotating along a circular path. The radiated sideband frequency is offset by +9960Hz or
−9960Hz
with respect to the carrier frequency. If the sideband
radiator rotates with a frequency of 30Hz, the Doppler Effect will cause the subcarrier to be frequency-modulated as a function of the azimuth. A circle with radius "R" of 7.5~6.5m is required in the frequency range from 108 to 118MHz,
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in order to obtain the frequency deviation of ±480Hz stipulated by the ICAO. The equation for determining R is derived from the formula for the Doppler Effect. The different methods used to generate the two 30Hz signals in the VOR and DVOR is of equipment-internal significance only. The VOR receiver installed in the aircraft has no means of determining externally whether the received signal originates from a VOR or DVOR ground station. However the DVOR permits a considerably more precise azimuth specification thanks to the wide-base antenna system which can be realized only by utilization of the Doppler Effect. The two 30Hz signals have a particular phase relationship with respect to one another and with respect to magnetic north in accordance with the azimuth. With an azimuth angle of 0° (North) the phase angle between the two signals is 0°. With an azimuth angle of 180° (South) the phase angle is 180°, with an azimuth angle of 90° (East) it is 90° and with an azimuth angle of 270° (West) it is 270°. The radio reference lines, along which the azimuth angle remains constant, are radial with respect to the DVOR installation. Fig.1-2 shows the phase relationship which is obtained between the reference signal and the direction dependent signal in various directions.
Fig. 1-2 Azimuth as a function of the phase angle 1.2.3 Doppler Effect and Direction-Dependent FM Fig. 1−3 shows generation of direction-dependent frequency modulation with the aid of the Doppler Effect. If omnidirectional antenna A is orbiting mechanically in an anticlockwise direction, the frequency measured by the two observers B1 and B2 will be increased or reduced due to the Doppler Effect -4-
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(providing the diameter "D" is negligible as compared with the distance of the observers from the system), depending on whether the antenna is moving towards the observers or away from them. The frequency changeΔ changeΔf is a function of the orbiting speed or the orbiting frequency fn, the diameter D of the orbit and the mean radiated wavelength λ 0. The relationship is expressed as follows: If antenna A begins its orbit at point 1 and continues via 2 and 3 to 4, the frequencies received by the two observers B1 and B2 will change as a function of time. If I f a reference signal with the same frequency is transmitted at the same time by an omnidirectional, central antenna M, the phase angle between the reference signal (of antenna M) and the changing frequency (of antenna A) will be in proportion to the azimuth (observer’s position), i.e. the phase relationship of signal M and A with respect to one another is a function of the azimuth. The reference point is magnetic north (point 1), where both signals are in-phase.
Fig. 1−3 Generation of the direction-dependent FM It can be seen from the frequency spectrum (Fig.1-4) that the azimuth-dependent frequency modulation of the DVOR is located on the subcarrier f 1= 9960Hz. The two sidebands (f 0+f 1) and (f 0 − f 1) are generated separately in the DVOR transmitter for this purpose, and radiated via "rotating" outer antennas. The powers and phase relationships of the sidebands with respect to the carrier are set such that when added in the far field an amplitude-modulated
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composite signal re-emerges. re-emerges. If the outer antennas for the two sidebands are then allowed to orbit in an anticlockwise direction, but with their phases reversed, the requirement for frequency modulation of the sidebands in the double sideband mode is fulfilled automatically, namely that an increase in the frequency in the upper sideband must be coupled with a lowering of the frequency in the lower sideband and vice versa. The depth of modulation of the individual frequencies can be adjusted within certain limits. The values which apply for the normal cases are: − 30
Hz navigation signal
− 9960
Hz auxiliary carrier
− Voice − Identity
30 % 30 % 30 %
code
10 %
Fig. 1−4 Frequency spectrum of the DVOR (VOR) omnidirectional radio beacon
Fig. 1−5 (D) VOR signal amplitude modulated with 30 Hz and 9960 Hz 1.2.4 Electronic Simulation of the Antenna Movement The subcarrier frequency deviation of ±480 Hz and the carrier frequency range of 108~118 MHz are the same as with the conventional VOR. Taking a mean carrier frequency of 113 MHz (λ= 2.65m) the equation below reveals that the orbit must have a diameter of 13.5m:
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The orbital movement of the sideband signals at an orbiting frequency of 30Hz is best implemented by electronic means. 50 fixed, equidistant single antennas are installed on the orbit for this purpose. They are fed in sequence via an antenna switching unit such that the focal point of radiation orbits at the desired velocity. If the double sideband method is used (f 0+f 1 and f 0−f 1), the two sidebands whose focal points of radiation are orbiting in the same direction are transmitted by antennas opposite one another on the orbital path. To achieve this effect the antenna switching unit activates sideband antenna 1 with the upper sideband (f 0+9960Hz) and sideband antenna 26 with the lower sideband (f 0−9960Hz) simultaneously (Fig.1−6a). When antennas 1 and 26 reach their radiation peak, the adjacent antennas 2 and 27 are activated. As soon as these reach their radiation peak, the upper sideband of antenna 1 is switched to 3 and simultaneously the lower sideband of antenna 26 is switched to 28 (Fig.1 −6b). This method of activation of the sideband antennas and the modulation of the sideband signals result in a continuous, almost smooth orbiting of the focal points of radiation of the upper and lower sidebands.
Fig. 1−6 Switching of the sideband antennas in the DVOR 1.2.5 Monitoring
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According to ICAO, Annex 10 all navigation systems must be permanently monitored for correct radiation by an independently operating monitoring system. In the case of the DVOR this signal monitoring is performed by one or two monitors, whereby signal components are obtained via equipment-internal coupling circuits and one (or two) monitor dipoles, and supplied to the monitor. In case of dual monitoring these are split by the monitor divider switch and transferred to the two monitors, whereby the monitor 1 signal processing is driven by monitor signal processor 1 and the monitor 2 by monitor signal processor 2 in order to select the various signals in accordance with a specified control sequence. The actual values of the signals are compared with nominal values by the processor. Any deviation from the nominal values exceeding specified tolerance thresholds always leads to an alarm and to an automatic switchover to the standby transmitter or shut down of the system.
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2. Configuration Table-Configuration of the Equipment Item 1
Title DVOR-RYS Transmitter
Num 50W/100W
Note
1 Including 48 Sideband
2
Alford Loop Antenna System
1
Antenna and 1 Carrier Antenna
4
Counterpoise
1
3
Monitor Antenna
1
4
DC Power Supply
1
5
RMMS-RYS
1
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Less than 4h Optional
Beijing Redyas Science & Technology Development Co.,Ltd
Transmitter
- 10 -
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Alford Loop Antenna
- 11 -
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Monitoring Antenna
- 12 -
Beijing Redyas Science & Technology Development Co.,Ltd
3
DVOR-RYS Technical
Specification
3.1 System Data Azimuth accuracy
Better than ±2°measured over flat ground at 0~40°elevation and 4 wave distance
Azimuth stability
Better than ±0.5° measured at the monitor
Coverage
Slant distance range in accordance with Attachment
C to Part I, Vol. I, ICAO Annex 10, depending on the transmitter power and the height of the antenna counterpoise above the ground
3.2 Equipment Data 3.2.1 Carrier Transmitter (CSB) Radio frequency range
108~117.95 MHz
Channel pattern
50 kHz, defined by synthesizer
Carrier frequency tolerance
±0.002%
Output impedance RF output power
50Ω 50W or 100W
Frequency control
crystal or synthesized
RF output stability
±0.5dB
3.2.2 Carrier Modulation Reference signal Modulation frequency
30Hz ±0.01%
Depth of amplitude modulation
30% ±1%,
Course setting range
0~359.9°, programmable
Identity Tone frequency
1020 Hz ±0.01 %
Keying (Morse code)
Sequence of max.4 letters, programmable
Repetition time
7.5s
Voice Range Stabilization and linearisation of carrier
300~3000 Hz, flat within ±3 dB with feedback loops for envelope and RF phase Modulation
Phase stability of sideband
20dB
Deviate from horizontal level omnidirectional pattern:
