(2) The D/U ratio between VHF NAVAIDS with a nominal 50 kllz frequency separation shall be -34 dB or greater. (-34 dB or -30dB are permissible; -40 dB is not.) Frequency assignments made under this criteria (called the "Final" criteria) insure protection to narrow bandwidth (i.e., 50 kHz) receivers considering both ground and airborne frequency tolerances.
minimum D/U ratio of -7 dB is required to insure protection to wideband (i.e., 100 kHz) receivers using 100 kHz (i.e., even multiples of 50 kHz) ground stations. This value is called the "Interim" criteria. In highly congested arts of the country, the "Interim" criteria may not allow frequency assignments to any new systems. New assignments in these areas would have to be made under the final criteria (-34 dB). As a safeguard when this is done, flight publications will indicate any nearby 100 kHz ground stations which cannot be used without the narrow bandpass characteristics associated with a 50 kHz receiver. This is required due to the insufficient rejection, in the 100 kHz receivers, to signals 50 kHz removed.
(3) The D/U ratio between VHF NAVAIDS with 100 kHz frequency separation shall not be less than -46 dB. In those parts of the country where 50 kHz assignments are made, the D/U ratio between stations with 100 kHz frequency separation shail not be less than -50 dB.
(4) The D/U ratio between VHF NAVAIDS with more than 100 kHz frequency separation shall not be less than -50 dB.
(5) Some peak power deterioration is allowed before the system is shut down. In order to account for this decrease in power, the actual D/U values used for station separation calculations are 3 dB more protective, e.g +23 dB vice +20 dB, -31 vice -34 dB, etc.
b. Interference Protection of OME/TACAN. The following interference signal protection ratios shal! be provided within the operational service volume of all DME/TACAN stations with a 95 percent time availability. This is done by controlling the station separation in certain cases.
_ The D/U signal ratio between co-channel DME/TACAN stations shall not be less than +8 dB.
The D/U signal ratio between adjacent channel DME/TACAN stations shall be as follows. The various D/U ratios have been established recognizing the spectrum control characteristics reflected in paragraph 124 and the spectrum differences between DME and TACAN.
(a) When the undesired station is a TACAN, the D/U ratio shall not be less than -42 dB.
(b) When the undesired station is an LDME (1000 W transmitter), the D/U ratio shall not be less than -39 dB.
(c) When the undesired station is a TDME (100 W transmitter), the D/U ratio shall not be less than -29 dB.
Chap 2 Par 29 Page 9
(3) The D/U ratio between DME TACAN stations with more than 1 MHZ frequency separation shall not be less than -50 dB.
(4) Some peak power deterioration is allowed before the system is shut down. In order to account for this decrease in power, the actual D/U values used for station separation calculations are 3 dB more protective,
e.y., +11 dB vice +8 dB, -39 dB vice -42 de, etc.
c. Protection of Service Volumes Which Extend Beyond National Borders.
Stations near the border are normally not frequency-protected for that airspace which lies beyond the national border. Standard service volume and expanded service volume protection may be provided upon proper coordination with Canada or Mexico. This must be done whenever specific airways, routes, or procedures beyond the border are based on ground stations in the U.S.A.
30. COMPONENT IDENTIFICATION SIGNALS. Each ground component shall transmit an identification signal consisting of three letters in International Morse It shall be transmitted at a rate of approximately 7 words per minute.
In addition, voice identification in accordance with paragraphs 3i through 33 may be provided by a VOR.
Identification Code Characteristics. The identification code characteristics shall conform to the following.
(1) The dots shall be a time duration of 0.l second to 0.125 second and the dashes three times the dot duration;
(2) The duration between dots and dashes of a code letter shall be equal to that of one dot plus or minus 10 percent;
(3) The time duration between consecutive letters of the identification code group shall not be less than three dots; and
(4) The total period of transmission of an identification code group shall not exceed 5 seconds.
The repetition and paragraphs 31 through 33.
31. INDEFENDENT COMPONENTS. whenever a facility is operated às a VOR, a UML, or a TACAN only, its identification signal shall be transmiited as follows.
a. For VOR providing only code identification signals, each 30 second interval is divided into either four or five equal periods. The code identification shall be transmitted during each period.
b. For VOR providing code and voice identification signals, each 30 second interval is divided into four equal periods. The code identification signal shall be transmitted during alternate periods or during three of four periods. Subject to paragraph 33, voice identification signals will occur during the remaining period (s).
Chan 2 Page 10 Par 29
when voice communication signals are being transmitted by a VOR, the /OR code identification sionals shall not be suppressed.
d. For DME and TACAN, the International Morse Code identification signal shall be repeated at intervals of 30 seconds.
32. IDENTIFICATION OF ASSOCIATED COMPONENTS. When a VOR and either a DME or TACAN are operated as cOTTocated components (see paragraphs 24 and 25), the identification signals shall conform to the respective requirements of paragraph 31 except that:
a. The identification code shall be the same for each component;
b. For VOR of paragraphs 3l.a and 3l.b, the DME or TACAN identification signal shall be transmitted during one of the periods allocated for VOR code identification. The VOR code shall not be transmitted during that period;
c. The international Morse Code identification signals of VOR, DME, and TACAN shall be synchronized and interlocked such that simultaneous identification transmissions of VOR/DME or VOR/TACAN or ILS/DME do not occur;
When voice communications are being transmitted on the VOR, the Code identification signals of DME and TACAN shall not be suppressed; and
e. Whenever one component is temporarily out of service, the component still operating shall transmit facility identification signals in accordance with paragraph 32 without regard to the facility type designation.
PRECEDENCE OF VOR VOICE COMMUNICATIONS. VOR voice identification signals shall not be suppressed for the duration of voice communications or broadcasts.
34. VOR VOICE COMMUNICATIONS SIGNALS. If required, a VOR may provide ground-to-air voice communications.
35. AIRBORNE COMPONENTS. Airborne components of the system consist of VOR components conforming to chapter 3, section 2 and DME and TACAN components conforming to the applicable requirements of chapter 4, section 2 of this Standard.
Chap 2 Par 31 Page 11
9/20/82 AC 00-31A 3o. SYSTEM TRAFFIC HANDLING CAPACITY. Each VOR and TACAN ground component of the system provides azimuth and facility identification information to an unlimited number of airborne components. DME and TACAN ground components can provide slant range adequate for a peak traffic load of 3375 interrogations per second.
NOTE: As the traffic density increases beyond full load, the system replies at a rate reduced proportionately to the number of additional interrogators. The ground component could be capable of servicing higher density traffic only if the airborne component could maintain satisfactory operations with reduced reply efficiency (see paragraph
130). The apparent change in numbers from Order 1010.55 dated 6/1/70 does not represent a change in beacon radiated power (for example, see Appendix 1). Therefore, increases in receiver sensitivities of existing airborne equipments are not required to achieve the same ranges that users have experienced in the past. Future designs should not be restricted by this fact.
37. VOR/TACAN/VORTAC SYSTEM AZIMUTH ACCURACY. System azimuth accuracy, expressed in terms of error, is a function of the error factors associated vith the ground and airborne components. The total system azimuth accuracy is + 4.5 degrees. (See Appendix 2)
38. SYSTEM DISTANCE ACCURACY. System distance accuracy is a function of the ground and airborne component accuracies. The component values in this standard provide a system distance accuracy of + 0.5 nmi (926 m) or 3 percent of the slant range distance, whichever is greater (95 percent probability), when the error values are combined by the root-sum-square method.
39. HIGH ACCURACY CERTIFICATION. Some system accuracy requirements exceed those specified in paragraphs 37 and 38. Some area navigation routes are an example. In order to support prescribed operations, flight inspections will validate the signal and certify its adequacy.
40.-49. RESERVED.
Chap 2 Page 12 Par 36
CHAPTER 3. VOR SYSTEMS SECTION 1. OPERATIONAL CHARACTERISTICS FOR VOR GROUND COMPONENTS 5C. INTRODUCTION. This section identifies standard signal characteristics and tolerances for the VOR portion of the system. These characteristics represent performance which shall be provided throughout the operational service volume as defined in paragraph 23.c.
polarized signals. POLARIZATION. The ground component antenna shall radiate horizontally Any vertically polarized signal components shall be at least 26 dB weaker than the horizontally polarized component.
52. RADIO FREQUENCY ACCURACY. The radio frequency carrier shall be within + 0.002 percent of the assigned frequency.
Signal power density of 20d/me gresent time availabilit a mimur (95 percent time availability) throughout the operational service volume as defined in paragraph 23.c.
the nearest aircraft position expected during sperations, the maximum signal power density expected at an aircraft will be on the order of -34 dBW/<.
NOTE: At 118 MHz, the value -120 dBW/m2 corresponds to - 123 dBW at the output of a lossless isotropic receiving antenna. The apparent change in numbers from Order 1010.55, dated 6/1/70, does not represent a change in radiated power (for example, see Appendix 1). Therefore, increases in receiver sensitivities of existing airborne equipments are not required to achieve the same service ranges that users have experienced in the past. Future designs should not be restricted by this fact.
54. AZIMUTH SIGNAL CHARACTERISTICS. The VOR shall radiate a radic frequency carrier with two associated 30 Hz modulations. The phase of one of these modulations shall be independent of the azimuth of the point of observation (reference phase). The other modulation (variable phase) shall differ from that of the reference phase by an angle equal to the magnetic bearing of the point of observation with respect to the VOR.
a. The radio frequency carrier shall be amplitude modulated by two signals in accordance with the following.
(1) Subcarrier Frequency Modulation. One signal component shall be a subcarrier of 9,960 Hz of constant amplitude.. • It shall be frequency modulated at 30 Hz having a deviation ratio of 16 ‡ l (i.e., 15 to 17) as follows.
NOTE: The deviation ratio of the signal from a Doppler VOR decreases from the value at the facility by the cosine of the vertical angle (l.e., will be as low as 8 at a point 60 degrees above the horizon).
Chap 3 Par 50 Page 13
(a) For the conventional VOR, the phase of the 30 Rz component of the FM subcarrier is fixed without respect to azimuth. It is termed the "reference phase."
(b) For ihe Doppler VOR, the phase of the 30 Hz component of the FM subcarrier varies with azimuth. It is termed the "variable phase."
(2) Subcarrier Frequercy and Accuracy. The subcarrier modulation mid-frequency shall be 9,960 Hz within +1.0 percent, and shall carry the 30 Hz frequency modulation.
(3) Subcarrier Modulation Frequency and Accuracy. The modulation frequency shall be 30 Hz within + 1.0 percent.
(4) Subcarrier Amplitude Modulation. Amplitude modulation of the subcarrier shall conform to the following.
(a) For the conventional VOR, the percentage of amplitude modulation of the 9,960 Hz subcarrier shall not exceed 5 percent.
(b) For the Single Sideband Doppler VOR, the percentage of amplitude modulation of the 9,960 Hz subcarrier shall not exceed 40 percent when measured at a point at least 1000 feet from the VOR. When Double Sideband Doppler VOR is installed, this modulation, for each sideband, shall not exceed 50 percent.
(5) Sideband Level Subcarrier Harmonics. When 50 kHz channel as poets are dated signal shall lot the the following ever H referenced to the level of the 9,960 Hz sideband.
Subcarrier Level 9,960 HZ O dB reference 2nd harmonic - 30 dB 3rd harmonic - 50 dB 4th harmonic and subsequent - 60 dB harmonics
55. 30 Hz AMPLITUDE MODULATION. The other signal component shall be 30 Hz amplitude modulation as follows.
a. For the conventional VOR, this component results from a rotating field pattern, the phase of which varies with azimuth. It is termed the "variable phase" and is of constant amplitude.
b. ror the Doppler VOk, this component of constant phase with relation to azimuth, is radiated omnidirectionally. It is termed the 'reference phase" and is of constant amplitude.
56. AMPLITUDE MODULATION FREQUENCY AND ACCURACY. The modulation frequency shall be 30 Hz within + 1.0 percent.
Chap 3 Page 14 Par 54
57. DEPTH OF REFERENCE AND VARIABLE PHASE MODULATIONS. The depth of modulation of the radio frequency carrier due to the 30 Hz or 9,960 Hz signals shall be within the following limits for each signal.
28 to 32 percent at all elevation angles from 0 to 5 degrees above the horizon; and
b. 25 to 35 percent at all elevation angles between 5 and 60 degrees above the horizon.
58. PHASE RELATIONSHIPS OF REFERENCE AND VARIABLE PHASE SIGNALS. The fundamental of the reference and variable phase modulations shall be in phase along the radial corresponding to magnetic north.
NOTE: The reference and variable phase modulations are in phase when the maximum value of the sum of the radio frequency carrier and the sideband energy due to the amplitude modulation signal occurs at the same time as the nighest frequency of the frequency modulation signal.
59. CODE IDENTIFICATION SIGNAL CHARACTERISTICS. The characteristics of the code identification signal shall conform to the following.
Tone Modulation Frequency and Accuracy. The modulation frequency shall be 1,020 + 50 Hz.
b. Depth of Modulation. The depth to which the radio frequency carrier is modulated by the code identification signal shall be:
(1) 5.0 ‡ 1 percent where voice services are provided.
(2) 4 to 10 percent at components where voice services are not provided.
60. VOICE IDENTIFICATION AND COMMUNICATIONS SIGNAL CHARACTERISTICS. The characteristics of voice identification and voice communications signals, when provided, shall conform to the following.
a. Voice Channel Frequency Response. Throughout the frequency range from 300 to 2,200 Hz, the frequency response characteristics for the voice channel shall be within 3 dB of the response at 1,000 Hz.
b. Depth of Modulation. The depth to which the radio frequency carrier is modulated by voice signals shall not be greater than 30 ‡ 2 percent.
6l. MONITORING. The radiated signal shall be monitored and removed from service upon recognition of unsafe operation.
62.-79. RESERVED.
Chap 3 Par 57 Page 15
SECTION 2. OPERATIONAL CHARACTERISTICS FOR VOR AIRBORNE COMPONENTS
80. INTRODUCTION. This section specifies functional capability and performance characteristics required of VOR airborne components. The term 'component" describes the complete aircraft installation. This includes the antenna and its transmission line, the receiver, electrical power source(s), identification and voice comnunications signal reproduction devices, and selector and display instrumentation devices for bearing and course indication. Airborne components used in the performance of aircraft operations under IFR must meet all requirements. For other aircraft operations the requirements are limited to those of paragraphs 80 and SC.
Components should be capable of performing as specified throughout the operational service volume of ground stations. The applicable performance requirements should be met when the ground stations are operating in accordance with this standard.
81. RECEIVER STABILITY. For each channel in use, the receiver's center requency shall be in accordance with Appendix 3. The receiver stability shall be ‡ 0.005 percent or better.
82. RECEIVER SENSITIVITY. Based on the signal power density of paragraph 53, the airborne component shall provide the sensitivity necessary to display navigation information to the accuracy specified. Clear and distinct reproduction of communications and identification signals shall be provided.
(See also Appendix l.)
83. REJECTION OF UNDESIRED SIGNALS. The airborne component shall provide undesired signal rejection characteristics adequate to assure the specified performance. For co-channel and adjacent-channel ILS and VOR signals, the D/U retios of paragraph 29 a shall apply.
84. MISTUNING PROTECTION. Mistuning by 50 kHz may result in erroneous information not readily apparent to the user if no VOR carrier is present on the tuned channel. Provision shall be made to protect against mistuning an airborne receiver by operational, mechanical, or electronic means.
85. FACILITY IDENTIFICATION AND VOICE SIGNALS. The airborne component shall provide the pilot with positive identification of the ground component.
86. BEARING AND COURSE DEVIATION INFORMATION. The airborne component shall provide devices for unambiguous determination of the aircraft magnetic bearing with respect to the selected ground component. This display shall show the aircraft deviation from the selected course.
87. COURSE DEVIATION DISPLAYS. The response, readability, and resolution of course deviation displays shall enable the pilot to determine the direction and extent of the aircraft deviation from the selected course.
88. WARNING FUNCTION. The airborne component shall provide a warning indication whenever the azimuth signals necessary for the prescribed performance are not present. This warning shall be clearly evident to the pilot.
Chap 3 Page 16 Par 80
9/20/82 AC 00-31A
89. ACCURACY OF BEARING AND COURSE DEVIATION INFORMATION. The total airborne component error, in bearing and course deviation information as displayed to the pilot, shall not exceed * 3.0 degrees (95 percent probability) at an bearing.
90. RADIATION. Radiation from airborne components shall not result in derogation of operational use to other system users or in the derogation of other aeronautical services.
91.-109. RESERVED.
Chap 3 Par 89 Page 17
CHAPTER 4. DME AND TACAN SYSTEMS SECTION. OPERATIONAL CHARACTERISTICS FOR DME AND TACAN
GROUND COMPONENTS
110. INTRODUCTION. This section identifies standard signal and performance characteristics for DME and TACAN ground components. These characteristics represent the performance which shall be provided throughout the operational service volumes defined in paragraph 23.c. Requirements apply to both DME and TACAN components, unless noted otherwise.
111. POLARIZATION. The ground component antenna shall radiate and receive a vertically polarized signal. Any horizontally polarized signal components shall be at least 26 dB weaker than the vertically polarized component.
112. TRANSPONDER RESPONSE TO INTERROGATION SIGNALS. The response of the transponder to interrogation signals shall conform to paragraphs 113 through NOTE: At the ground component antenna, the presence of Ci:
signals within I 3.0 MHz of the nominal value of the interrogation frequency at a signal power density of -l13 dBW/m or more, will normally derogate the performance of the system. Steps should be taken to avoid this situation.
113. INTERROGATION RADIO FREQUENCY. For each channel in use, the center frequency of the transponder's interrogation and reply frequencies shall be in accordance with Appendix 3.
114. SENSITIVITY TO INTERROGATION SIGNALS. Transponder sensitivity is specified as that minimum value of peak pulse power density (prior to ntercept by the ground component antenna) which will result in a transpondel reply efficiency of 70 percent. (See Appendix l) NOTE: Ground components may not respond to interrogations as specified if the difference in level of the constituent pulses of interrogation pulse pairs is greater than 1 dB.
115. ON-CHANNEL SENSITIVITY. For interrogation signals within ‡ 100 kHz of the assigned frequency, having a repetition rate no greater than 200 pulse pairs per second and pulse pair spacing of exactly 12.0 microseconds (36.0 microseconds for Y channel), DME sensitivity shall be not less than -101.5 than -104.5 dBu/m same conditions, the TACAN sensitivity shall be not less NOTE: At 1150 MHz, the value -101.5 dBW/m2 corresponds to -124.0 dBW at the output of a lossless isotropic receiving antenna. Similarly, the value -104.5 dBW/m? corresponds to - 127.0 dBW. (See Appendix 1) Chap Par 110 Page 19
116. SENSITIVITY AT OTHER PULSE SPACINGS. When the spacing of the constituent pulses of interrogation pulse pairs differs from the design center value (12.0 microseconds for x channel; 36.0 microseconds for Y channel) by + 0.5 microseconds or less, the sensitivity of paragraph 115 shall not be reduced by more than 1 dB.
more from nominal, the reduction in sensitivity shall be at least 70 dB with respect to the level of paragraph l15.
117. VARIATION OF SENSITIVITY WITH INTERROGATION LOADING. When the beacon is loaded with 3175 additional pulse pairs per second at a level of -65 dBm (referenced at the input to the transponder receiver with the transponder's echo suppression circuits disabled), the sensitivity of the receiver shall not be reduced by more than 1 dB from the value measured in paragraph 115.
118. SENSITIVITY TO ADJACENT CHANNEL INTERROGATIONS. Interrogation signals removed 900 kHz or more from the assigned channel interrogation frequency and laving an amplitude up to 80 di above the on-channel sensitivity or the component shail not elicit a reply from that component.
IlS. TRANSPONDER DEAD TIME. Dead time is the time immediately following an accepted interrogation decode for reply processing, during which succeeding interrogations receive no reply. The transponder dead time shall normally be the treconds f or 60 microseconds for X channels (72 microseconds for Y channels).
120. ECHO SUPPRESSION DEAD TIME. The retriggerable blanking gate (RTBG) (see paragraph 145.b) is typically set such that the effective dead time is a nominal 150 microseconds. When required for a particular site, the effective dead time may be increased up to a nominal 250 microseconds.
121. TRANSPONDER OUTPUT SIGNAL CHARACTERISTICS. The transponder shall conform to paragraphs 122 through 150.
122. FREQUENCY STABILITY. For each channel in use, the center frequencies of the ground station's transmitter and receiver shall be in accordance with qui ment uresed arter liy ee tabi trent er reer stat ions shall be ‡ 0.002 percent or better.
NOTE: Stabilities of older equipment need not be increased to + 0.001 percent.
123. SIGNAL STRENGTH IN SPACE. Within that part of the operational service ve t part or che operatonat sor vice votume that a betor 18, 00 ret 15,.496 above 18,000 feet (5,486 m) AGL, a minimum signal power density
m) AGL, a minimum signal power density of -86.0 dBW/m< shall be provided.
Signal power shall be determined by the average over one second ot the equivalent peak pulse voltage waveform. At the nearest aircraft position expected during operations, the maxımum signal power density expected durıng liaht will be on the order of -17.0 dBW/m< .
Chap 4 Page 20 Par 116
NOTE: At 1213 MHz, the value -91.5 dBW/m2 corresponds to
- 114.5 dik at the output of a lossless isotropic receiving Similarly change in antenna. Similarly, -86.0 dBW/m- corresponds to -109.0 dBW. The apparent change in numbers from the old standard does not represent a change in beacon radiated power (for example, see Appendix 1). Therefore, increases in rece!ver sensitivities of existing airborne equipments are not. required to achieve the same service ranges that users have experienced in the past. Future designs should not be restricted by this fact.
124. RADIO SPECTRUM. The spectrum of the pulse modulated signal shall be as follows.
a. The equivalent isotropic radiated power (EIRP) contained in a 0.5 MHz band centered on a frequency either 0.8 MHz above or 0.8 MHz below the nominal channel frequency shall (in both instances) not exceed 200 milliwatts (except that the power relative to center frequency shall not exceed -50 dB).
b. The EIRP contained in a 0.5 MHz band centered on a frequency either
2.0 MHz above or 2.0 MHz below the nominal channel frequency shall (in both instances) not exceed 2 milliwatts (except that the power relative to center frequency shall not exceed -70 dB).
c. Each lobe of the spectrum will be generally of lesser amplitude than the adjacent lobe nearer the nominal channel frequency.
125. SPURIOUS RADIATION. The RF output level, during the interval between occurrence of the desired pulse pairs, shall not exceed a level which is 80 dB below the maximum power level during a pulse. In addition, between the pulses of each pair there shall be an interval for 1.0 microsecond or greater in length during which the RF output level does not exceed a level which is 50 dB below the maximum power level of the weaker pulse of the pair.
126. PULSE SHAPE. The following, as limited by the requirements of paragraphs 124 and 125, shall apply to all radiated pulses.
a. Pulse Rise Time. The time required for the pulse to rise from 10 to 90 percent of its maximum voltage amplitude shall not be less than 0.1 microsecond nor more than 3.0 microseconds.
b. Pulse Top. Between the points on the leading and trailing edges which are 95 percent of the maximum voltage amplitude, the instantaneous amplitude of the pulse shall not fall below a value which is 95 percent of the maximum voltage amplitude of the pulse.
c. Pulse Duration. The pulse duration, as measured at the 50 percent maximum voltage amplitude points, shall be 3.5 1 0.5 microseconds.
d. Pulse Decay Time. The pulse decay time, trom the 90 percent point to the 10 percent point of the maximum voltage amplitude, shall be such that the remaining requirements of this standard shall be satisfied.
Chap 4 Par 123 Page 21