Appendix 1 APPENDIX 1. COVERAGE.
RADIO PROPAGATION. Propagation losses vary as a function of time. For a given EIRP, the power density at a point in space will fluctuate. In addition, propagation loss will vary from site to site. This variation is a function of several factors including atmospheric refractivity, surface reflectivity, wave polarization, etc. Since the VOR/DME/TACAN system is a safety service, signals must be highly reliable. With this in mind, conservative assumptions have been made for the inputs to the propagation model. Figures 2 through 13 show standard VOR, DME, and TACAN signal strengths (95 percent time availability) at varicus points in space. A time availability of 95 percent means that, at a given point in space, the instantaneous signa! strength will be greater than or equal to the value showr 95 percent of the time. Although propagation losses will differ from site to site, the signal strength curves of this appendix are recommended for purposes of standardization. It is important to remember that for the distance function of DME and TACAN both the ground-to-air and air-to-ground transmissions must be considered.
GROUND STATION. The EIRP's and resultant signal strength in space curves given in Figures 2 through 13 are nominal. Allowances should be made for different EIRP's and for other variations in stalion characteristics.
Some ground stations may have higher cable losses (e.g., mountain top installations sometimes require longer cable runs). In addition, intervening terrain may increase ihe transmission path loss. Should this occur, it may be necessary to reduce the service volume accordingly.
VOR COVERAGE.
The power density specified in paragraph 53 (-120 dBW/m?) is equivalent to -123 dBW power available at the output of a lossless isotropic antenna (at 118 MHz). Allowance nust be made for the airborne antenna and for cable and insertion losses. Users will balance their airborne power budgets in different ways. Two examples are shown below.
Еx3mple 1 Example 2 Power Available - 123 dBW - 123 dBW Airborne Antenna Gain* +2.2 dBi -l dBi Airborne Losses -2.2 dB -4 d3 Receiver Sensitivity - 123 dB!! - 728 dBW Many other examples could be given. It is the user's responsibility to insure that the airborne installation will allow proper operation at the minimum signal strength of paragraph 53. (In considering airborne antenna gain, antenna patiern variation should not be neglected.)
*NOTE: Does not consider variations due to antenna locations or other factors which influence antenna gain due to shielding.
Par 1 Page I
Appendix 1
4. DME/TACAN (UPLINK) COVERAGE
a. The power densities specified in paragraph 123 are referenced to the powers available at a point in space. Allowance must be made for the airborne antenna and for cable and insertion losses. Users will balance their airborne power budgets in different ways. Two examples of how users might balance their airborne power budgets for the DME and TACAN are shown as follows:
Example 1 Example 2
DME DME (100W) TACAN (100W) TACAN Power Available - 109.0 - 114.5 dBW - 109.0 - 114.5 dBW Airborne Antenna Gain* +2.0 • +2.0 dBi +0.5 +0.5 dBi Airborne Losses -3.0 -3.0 dB - 1.5 - 1.5 dB Rx Sensitivity - 110.0 - 115.5 dBW - 110.0 - 115.5 dBW
b. Many other examples could be given. It is the user's responsibility to insure that the airborne installation will allow proper operation at the minimum signal strengths of paragraph 123. An airborne DME installation with 1 dB of loss (antenna pattern, cable and insertion losses, signal splicters, etc.) would require a 1°1100 55M. An stone TAch In. When the sensitivity of -110.0 dBW. An airborne TACAN installation with | dB of loss would require a sensitivity of -115.5 dBW. When the total loss is different than 1 dB, a corresponding adjustment must be made to determine the required sensitivity. In considering airborne antenna gain, antenna pattern variation should not be neglected.
5. DME/TACAN (DOWNLINK) COVERAGE.
a. The minimum power density specified in paragraph 178 for the input to the ground station antenna is -99.0 dBW/m? for DME and - 102.5 dBW/m?
for TACAN. These power density values are necessary to generate a reply efficiency of 70 percent from the transponder during periods when the transponder is under heavy load and when the interrogation signal is within + 100 kHz of the nominal channel frequency and its pulse pair spacing is within +0.5 microseconds of the nominal system value. The association of Interrogator signal strength and transponder sensitivity is as follows.
*Note: Does not consider variations due to antenna locations or other factors which influence antenna gain due to shielding.
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Appendix 1
DME TACAN -94.0 -97.0 dBm Transponder Sensitivity per paragraph 115 + 6.7 + 3.0 dB Net coupling to receiver per
(1) +8.2 dBi DME Antenna Gain on horizon -1.5 dB Net Losses (cable and insertion)
(2) +4.5 dBi TACAN Antenna Gain on horizon -1.5 dB Net Losses (cable and insertion) -87.3 -94.0 d8m Receiver input for 70 percent Efficiency per paragraph 115 + 2.0 + 2.0 dB Sensitivity Reduction per paragraphs 116 and 117 -85.3 -92.0 dBm : Receiver Input for 70 percent efficiency
b. It is the user's responsibility to provide that signal strength to insure proper operation for those conditions stated in paragraph 178. For the requirement of 70 percent reply efficiency:
DME TACAN -85.0 -92.0 dBm Receiver Input per conditions of paragraph 178
- 0.7 - 3.0 dB Net coupling per Antenna -91.7 -95.0 dBm Signal Strength at the antenna input -99.2 - 102.5 dBW/m2 Power Density at the antenna input -99.0 -102.5 dBW/mC Value used in paragraph 178
6. TIME AVAILABILITY. At a point in space, signal strength will vary with time even when the ground transmitter's EIRP remains constant. A similar statement could be made for D/U signal ratios. This variation is largely due to propagation effects under different environmental conditions. Examples include atmospheric refractivity, seasonal changes in ground cover, and as are aiso inund cover Although it surface reflectivity. Numerous other factors are also involved. Although it is difficult to describe accurately all the variables involved, the situation statistical discussion of reliability, is time availability. It is that can be adequately covered by statistical treatment. A helpful concept, in a that a given sight strengen or bly natio unction fe ne percentage of time that a given signal strength or D/U ratio is met or exceeded. Figure I shows an example of signal strength as a function of time availability. For a time availability of 95 percent, the signal strength is
- 120 dBW/m?. This means that a signal strength of -120 dBW/m? or greater is present 95 percent of the time. For a time availability of 50 percent, the signal strength is -117 dBW/m' at the same point in space assuming the same constant ground station characteristics. In a similar manner, the signal strength present for any given percentage of the time can be read from the graph. This graph does not, however, take transmitter downtime into account.
Par 5 Page 3
Appendix 1 FIGURE 1. SIGNAL TIME AVAILABILITY SIGNAL STRENGTH IN SPACE (dBW/m2) 130 150 -01 5 10 50 90 95 99 • 99.9 99.99
PERCENT TIME Page 4
Appendix 1
TUDE IN THOUSANDS OF I FIGURE 2. VOR SIGNAL STRENGTH IN SPACE - LONG RANGE DISTANCE FROM THE DESIRED STATION IN Em 180 200 220 240 200 280 200 320 /MA 3OL- DISTANCE FROM THE DESIRED STATION IN MO 100 120 140 160 VOR SIGNAL STRENGTH IN SPACE 100 W (20 OBW) Tranamitter Power 3 d8 Cable Losses (Ground) 22 dBi Mainbeem Antenna Gain 19.2 dBW EIRP, 118 MHz
- •
ALTITUDE (AGLI IN THOUSANDS OF Page 5
9/20/82 AC 00-31A Appendix 1
ALTITUDE IN THOUSANDS OF METER FIGURE 3. TAGAN (RTB-2) SIGNAL STRENGTH IN SPACE - LONG BANGE мар 9 DISTANCE FROM THE DESIRED STATION IN km 160 100 200 220 240 260 140 DISTANCE FROM THE DESIRED STATION IN mmi 120 M8P 100 120 140 60 20 SIGNAL STRENGTH IN SPACE OBWI Transmiller Powe Losses (Ground) beem Antenna Gain RIP. 1213 MHZ
•
LTITUDE (AGLI IN OUSANUS OT Page 6
Appendix 1
ALTITUDE IN -ş FIGURE. CARDION OME SIGNAL STRENGTH IN SPACE - LONG BANGE 100 200 220 200 200 2á0 200 220 20 360 3é0 ISP DISTANCE FROM THE DESIRED STATION IN km do 100 120 140 180 SIGNAL STRENGTH IN SPACE dEW) Tramamitter Power Losses (Ground) nbeem Antenne Gain 1213 MHz EIRP.
CARDION 1000 W
ALTITUDE (AGL) IN THOUSANDS OF FEE Page 7
Appendix 1
- 30 FIGURE 5, CARDION DME SIGNAL STRENGTH IN SPACE - LONG RANGE 100 DISTANCE FROM THE DESIRED STATION IN mmi RDION DME SIGNAL STRENGTH IN SPACE ẨвУ 100 W (20 dEW) Transmitter Power seei (Ground) um Antenne Gain 1213 MHz
1.5 da Callo Lo .4 dBI Mainbe • dBW EIRP
11.
- &
ALTITUDE (AGLI IN THOUSANDS OF FEET Page 8
Appendix 1
ALTITUDE IN THOUSANDS OF METER FIGURE 6. MONTEX DME SIGNAL STRENGTH IN SPACE - LONG RANGE DISTANCE FROM THE DESIRED STATION IN km 140 DISTANCE FROM THE DESIRED STATION IN Ai 140 160 100 200 220 260 60 60 100 120 MONTEK DME SIGNAL STRENGTH IN SPACE 1000 W (30 dBW) Tranemitter Power 1.6 de Cable Losses (Ground) 8.8 dBI Mainbeem Antenna Gain 37.3 dBW EIRP. 1213 MHz M8P 9'6L 8P !
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Appendix 1
THOUSA MCS OF FIGURE 7. MONTEK DME SIGNAL STRENGTH IN SPACE - LONG RANGE DISTANCE FROM THE DESIRED STATION IN km 129 DISTANCE FRON THE DESIRED STAI 100 120 740 MONTEK DME SIGNAL STRENGTH IN SPACE 1 Transmitzar Powe Jesse (Ground) Ansense Gain 100 W 120 di 1.5 dB Cable 77.3 doW EIR
- 8 NOTE: Thi!
LTITUDE LAGLI IN THOUSANDS OF FEET ge 10
AC 00-31A Appendix 1
ALTITUDE (AGLI IN HUNDREDS OF METERS dBIV/m2 мар FIGURE 8. VOR SIGNAL STRENGTH IN SPACE - SHORT RANGE DISTANCE FROM THE DESIRED STATION IN km DISTANCE FROM THE DESIRED STATION IN ON VOR SIGNAL STRENGTH BW) Transmitter Fower EIRP 120
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Appendix 1
ALTITUDE (AGLI IN HUNDREDS OF METERS FIGURE 9. TACAN (RTB-2) SIGNAL STRENGTH IN SPACE - SHOR I RANGE DISTANCE FROM THE DESIRED STATION IN km 35 DISTANCE FROM THE DESIRED STATION IN Ni STRENGTH IN SPACE ans Qain
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