ACP-WGF/16-WP16
NSP/SSG WP/XX
NAVIGATION SYSTEMS PANEL (NSP)
Working Group 1 Meeting
Montreal, Canada
December 11-15, 2006
Agenda Item : Update of guidance material on VOR and DME service volumes
DME Power Availability Curves and Service Volumes
Presented by Bruce DeCleene
(Prepared by Robert Frazier)
SUMMARY
This Working paper is in response to Question SSG9/9: To
provide
further
background
information
on
the
“discontinuities” in the DME propagation curves, whether they
are due to antenna lobbing or due to multipath
1.
INTRODUCTION
1.1
Recommendation 6/15 adopted by the Eleventh Air Navigation Conference (AN-Conf/11wp-201) calls for updating of SARPs for radio navigation aids in Annex 10, Volume 1 and in
particular for revision of guidance material on DME and VOR service volumes. Conventional
Navaids and Testing Subgroup (CN&TSG) at its October 2005 meeting in Montreal adopted an
action calling for development of update to the guidance material on VOR and DME service
volumes and coverage prediction. According to these actions, the United States presented a Working
Paper (WP-38) titled “DME Power Availability Curves and Service Volumes” at the WG1/2
meeting in Brussels during May 8-18, 2006 and another Working Paper (WP-XX) at the WG1
meeting in Montreal during October 13-15, 2006. .
1.2
This working paper presents further information on the discontinuities in the DME
propagation curves, whether they are due to antenna lobing or due to multipath (Question SSG9/9).
2. DISCUSSION
2.1
The U.S. National Standards for DME presents five different power density figures for
typical DME and TACAN facilities based on the minimum power density requirements of -91.5
dBW/m² in the airspace above 18,000 feet and –86.0 dBW/m² below 18,000 feet in the United
States. One of these five figures is shown in Figure 1 below. It is for a Cardion 1,000 watts DME
facility having 1.5 dB cable losses and an antenna gain of 11.4 dBi. The effective isotropic radiated
power (EIRP) of this facility is 39.9 dBW at 1213 MHz.
ACP-WGF/16-WP16
NSP WG1 WP/XX
Figure 1. US Power Density Curves from US National Standards for DME
2.2
The discontinuities are shown in all three curves in Figure 1 above. For example, the
discontinuities for the -91.5 dBW/m² curve are located at approximately 100 NMI at the altitudes
of approximately 8,000-10,000 feet.
2.3
The PC based IF-77 model was used to investigate the cause of the discontinuities.
Figure 2 shows a -91.5 dBW/m² power density curve for the 1 KW Cardion DME system
generated by the PC based IF-77 model with the lobing option selected to “No Lobing”. Figure
3 (Incl Lobing) also shows a -91.5 dBW/m² power density curve for the same DME system but
with the lobing option selected to “Incl Lobing” which means lobing is on.. As can be seen, the
power density curve in Figure 2 (No Lobing) is very close to the DME power density curve from
the U.S. National Standards document in Figure 1. This is illustrated in Figure 4. Although we
are continuing to study the model and learn exactly how the model works, based on comparisons
so far, it is likely that the power density curves in the U.S. National Standards were generated by
this version of the IF-77 model with the lobing option selected to “No Lobing”. Figure 5 shows
the other IF-77 parameter settings used for both Figure 2 and 3.
ACP-WGF/16-WP16
NSP WG1 WP/XX
Figure 2 (No Lobing)
Figure 3 (Incl Lobing)
ACP-WGF/16-WP16
NSP WG1 WP/XX
Figure 4 (U.S. National Standards curves in blue overlaid on Figure 2)
Figure 5 ( IF-77 Parameter settings)
ACP-WGF/16-WP16
NSP WG1 WP/XX
2.4
Analysis of Figures 2 shows that the power density curves at the upper left hand corner
display the characteristics of lobing effect even though the lobing option was selected to “No
Lobing”. This portion of the curves was then compared with the power density curves in the
same area in Figure 3 (Incl Lobing) which are the power density curves with lobing on. It was
noted that these curves are identical. This indicates that the IF-77 model considers lobing effect
regardless of the lobing option selected. It appears at this time that when the lobing option is
selected to “No Lobing”, the IF-77 model does not plot lobing patterns except in the cone of
silence region. Figure 6 below shows the smooth “no lobing” -91.5 dBW/m² curve ( DME
Curve from Figure 2) overlaid on the lobing patterns in Figure 3. Comparison of the smooth “no
lobing” -91.5 dBW/m² curve in Figure 6 with to the “lobing on” curves indicates that the “no
lobing” option is designed to generate a very conservative curve.
Figure 6
2.5
We have not been able to isolate the algorithm used in the IF-77 model to plot smooth
“no lobing” curves. We continue to investigate the cause of the discontinuities and plan to
submit an updated working paper at a future meeting.
3. CONCLUSION
ACP-WGF/16-WP16
NSP WG1 WP/XX
The Working Group is invited to review the information provided in this working paper as an
interim response to SSG Q 9/9, and to use it as it sees fit.