ACP/WG-B/WP___

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

Working Group B

Tokyo, Japan

January 28 – February 6, 2004

VDL Mode 3 to DSB-AM Interference Testing

Agenda Item b: VDL frequency assignment planning criteria for VDL Mode 3

Presented by George Sakai

Federal Aviation Administration

United States of America

Prepared by Ed Coleman

Federal Aviation Administration

SUMMARY

This report outlines the status of current testing of avionics VDL-3 to avionics DSB-AM receiver using “red label” (pre-certification) avionics equipment. The test method employed was the technique agreed to at the 9th AMCP WG-B meeting in Bretigny, France in July 2000 and used the 18dB signal-to-pulse interference level agreed to at the 11th AMCP WG-B meeting in Montreal, Canada. To date, the test data is in agreement with previous work, which tested prototype equipment, that indicated frequency planning beyond the fourth-adjacent channel is not necessary. Testing is planned to continue with additional avionics prototypes and certified (i.e., “black label”) VDL Mode 3 radios.

1.0Introduction

This paper reports the status of current test efforts undertaken by the FAA in regards to developing frequency-planning criteria for VDL Mode 3. As part of the FAA’s NEXCOM program, three avionics vendors[1] have developed VDL Mode 3 avionics and have been participating in test and demonstration efforts at the FAA’s William J. Hughes Technical Center. Upon completion of the most recent demonstration effort, these avionics were made available for testing, to aid in the development of frequency planning criteria. This paper discusses the status of the current test effort and plans for continuing work.

2.0Test Procedure

The test described in this report utilized the procedures agreed to during the 9th Working Group B meeting and the 18dB signal-to-pulse criteria agreed to in the 11th meeting report. A diagram of the test setup is shown below:

Figure 1. Test Setup

In this setup the desired signal is tuned to 136.000 MHz, –82dBm, 30% modulated 1kHz tone at the input of the victim receiver. The receiver was adjusted to provide 1-volt peak-to-peak audio output with this desired signal. At each frequency-offset condition, the RF attenuation between the victim DSB-AM receiver and the VDL Mode 3 transmitter was varied until the audio interference visible at the victim receiver output measured 0.125 volt peak-to-peak (yielding the 18dB signal-to-pulse ratio). At this point the interfering RF level was recorded.

3.0Test Results

Table 1 shows the required physical separation for the first through the fourth adjacent channels in order to achieve an 18dB signal-to-pulse ratio at the victim receiver’s audio output. Two separation distances are of special interest: the 2000ft vertical separation and the 0.6nmi horizontal separation currently used for frequency assignments in the U.S. national airspace. In order to ensure that no interference occurs at the 2000ft vertical separation, frequency planning should ensure that no two aircraft within this range are using channels within +/- 100kHz (or the fourth adjacent channel). These results agree with previous work (see WP6 from the 11th meeting of WG-B), which recommended, “no planning at the fourth channel”.

Table 1. Required separation distances to achieve 18dB signal-to-pulse

Adjacent
Channel / Victim RX / Attenuator
Setting
(dB) / Path Loss
(dB)
Note 1 / Undes Pwr @
victim RX (dBm)
Note 2 / Req’d separation
distance (ft)
Note 3 / Req’d separation
distance (nmi)
RX – A / 74 / 97 / -55 / 44732 / 7.4
1 / RX – B / 79 / 102 / -60 / 79546 / 13.1
RX – C / 73 / 96 / -54 / 39867 / 6.6
RX – A / 60 / 83 / -41 / 8925 / 1.5
2 / RX – B / 65 / 88 / -46 / 15872 / 2.6
RX – C / 60 / 83 / -41 / 8925 / 1.5
RX – A / 50 / 73 / -31 / 2822 / 0.5
3 / RX – B / 52 / 75 / -33 / 3553 / 0.6
RX – C / 45 / 68 / -26 / 1587 / 0.3
RX – A / 45 / 68 / -26 / 1587 / 0.3
4 / RX – B / 47 / 70 / -28 / 1998 / 0.3
RX – C / 44 / 67 / -25 / 1415 / 0.2

Sample Calculation for RX-A first adjacent channel:

Path Loss
(dB) / = / Dir Coup
Factor (dB) / + / Var.
Atten Setting
(dB) / + / Coupler Loss
(dB)
97 / = / 20 / + / 74 / + / 3

Sample Calculation for RX-A first adjacent channel:

Pwr @
victim RX
(dBm) / = / TX PWR
(dBm) / - / Path Loss (dB)
-55 / = / 42 / - / 97

Sample Calculation for RX-A first adjacent channel:

Convert path loss into distance using the relationship / Solving for distance given the path loss yields: / Convert ft to nmi:
Path loss = 20log(ft) + 20log(MHz) - 37.45 dB / ft = 10^ {[path loss + 37.45 - 20log(MHz)] /20 }
44,732 = 10^ {[ 97 + 37.45 - 20log(118) ] /20 } / 7.4 =
44732 / 6076

In addition to the adjacent channel performance data presented above, co-channel performance data is available for receiver C (RX – C). In order to achieve an 18dB signal-to-pulse ratio with co-channel interference, a D/U ratio of 20dB was required (i.e., with a desired signal = -82dBm, and an undesired signal = –102dBm). This is significantly better than the current 30 dB developing using prototype equipment. We do not currently recommend any changes to existing co-channel frequency engineering criteria based on this one “data point” however.

4.0 Conclusions:

The data collected on the current generation of Mode 3 avionics is largely in agreement with previous studies using simulated avionics transmissions that had predicted no-frequency planning for the 4th adjacent channel.

5.0Recommendations:

The group is invited to consider the conclusions in this paper as supporting material in developing the frequency planning criteria for VDL Mode 3 to DSB-AM interference. It is further recommended that this frequency engineering criteria be further validated by continued testing of certifiable VDL transceivers.

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[1] Two Air Carrier manufacturers: Rockwell-Collins and Honeywell, and one general aviation: Avidyne