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runway. Care is also to be taken that where distance information is required in the runway region, the selected site is not
likely to cause the interrogator to lose track due to excessive rate of change of velocity.
23/11/06 ATT C-70
Attachment C Annex 10 — Aeronautical Communications
7.1.7 Geographical separation criteria
In order to allow consideration of actual antenna designs, equipment characteristics, and service volumes, the signal
ratios needed to assure interference-free operation of the various facilities operating on DME channels are provided in 7.1.8,
7.1.9 and 7.1.10. Given these ratios, the geographical separations of facilities may be readily evaluated by accounting for
power losses over the propagation paths.
7.1.8 Desired to undesired (D/U) signal ratios at the airborne receiver
7.1.8.1 Table C-4 indicates the necessary D/U signal ratios needed to protect the desired transponder reply signal at an
airborne receiver from the various co-frequency/adjacent frequency, same code/different code, undesired transponder reply
signal combinations that may exist. For initial assignments, the D/U ratios necessary to protect airborne equipment with
6-microsecond decoder rejection should be used. In making an assignment, each facility must be treated as the desired source
with the other acting as the undesired. If both satisfy their unique D/U requirement, then the channel assignment may be
made.
Table C-4. Protection ratio D/U (dB)
Type of assignment A B
Co-frequency:
Same pulse code
Different pulse code
8
8
8
–42
First adjacent frequency:
Same pulse code
Different pulse code
–(Pu – 1)
–(Pu + 7)
–42
–75
Second adjacent frequency:
Same pulse code
Different pulse code
–(Pu + 19)
–(Pu + 27)
–75
–75
Note 1.— The D/U ratios in column A protect those DME/N interrogators operating
on X or Y channels. Column A applies to decoder rejection of 6 microseconds.
Note 2.— The D/U ratios in column B protect those DME/N or DME/P interrogators
utilizing discrimination in conformance with 3.5.5.3.4.2 and 3.5.5.3.4.3 of Chapter 3 and
providing a decoder rejection conforming to 3.5.5.3.5 of Chapter 3.
Note 3.— Pu is the peak effective radiated power of the undesired signal in dBW.
Note 4.— The frequency protection requirement is dependent upon the antenna
patterns of the desired and undesired facility and the ERP of the undesired facility.
Note 5.— In assessing adjacent channel protection, the magnitude of D/U ratio in
column A should not exceed the magnitude of the value in column B.
ATT C-71 23/11/06
Annex 10 — Aeronautical Communications Volume I
7.1.8.2 Accordingly, DME channel assignments depend upon the following:
a) For co-channel assignments: This condition occurs when both the desired and undesired signals operate on a
channel (W, X, Y or Z) that is co-frequency, same code. The D/U signal ratio should be at least 8 dB throughout the
service volume.
b) For co-frequency, different code assignments: This condition occurs when one facility operates on an X channel
with the other on a W channel. A similar Y channel and a Z channel combination also applies.
c) For first adjacent frequency, same code assignments: This condition occurs when both the desired and undesired
facilities are of W, X, Y or Z type.
d) For first adjacent frequency, different code assignments: This condition occurs when one facility operates on an X
channel with the other on a W channel, but with a frequency offset of 1 MHz between transponder reply frequencies.
A similar Y channel and a Z channel combination also applies.
e) For second adjacent frequency, same or different code assignments: The second adjacent frequency combinations
generally need not be frequency protected. However, special attention should be given to Note 4 of Table C-4,
especially if the undesired facility is a DME/P transponder.
7.1.9 Special considerations for DME Y and Z channel assignments
Assignment of a Y or Z channel whose reply frequency is 63 MHz removed from the reply frequency of another channel
(either a W, X, Y or Z channel) or vice versa requires a distance separation of at least 28 km (15 NM) between facilities.
7.1.10 Special considerations for DME W or Z channel assignments
Assignment of a W or Z channel whose reply frequency is 63 MHz removed from the reply frequency of a Y channel or vice
versa requires a distance separation of at least equal to the service volume range of the Y channel facility plus 28 km (15 NM).
7.1.11 Special considerations for making pulse spectrum measurements
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