another look at signal leakage: the need to monitor at low and high frequencies ron hranac technical...
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Another Look at Signal Leakage:The Need to Monitor at Low and High
Frequencies
Ron HranacTechnical Leader
Cisco Systems, Inc.
Greg TresnessPresident
Arcom Digital, LLC
FCC Rules and Signal Leakage§76.605(a)(12): Maximum allowable signal leakage field strengths
§76.609(h)(1) through (5): How to perform measurements
§76.613: Harmful interference
§76.617: Leakage from devices inside the home
§76.610: Spells out sections of rules that apply for aeronautical band operation (§§76.605(a)(12), 76.611, 76.612, 76.613, 76.614, 76.616, 76.617, 76.1803 and 76.1804)
Frequencies Signal leakage limit (micro-volt per meter)
Distance in meters (m)
Less than and including 54 MHz and over 216 MHz 15 30Over 54 up to and including 216 MHz 20 3
Is Aeronautical Band Monitoring Enough?Monitoring for leakage outside the 108-137 MHz aeronautical band was not a major concern until one to two years ago, when reports of cable-related interference to long term evolution (LTE) service in the 698-806 MHz spectrum began to surface
Field measurements have shown that it is surprisingly easy to find leakage in the 700+ MHz spectrum
In many instances when high frequency leakage exists, there is little or no measurable leakage at low frequencies, and vice versa.
Note approximately 18 dB difference between leakage field strength at Ch. 14 (121.2625 MHz) and Ch. 85 (591 MHz)
High Frequency Leakage exampleVerizon tower-to-UE
downlink signals (746-756 MHz)
Verizon UE-to-tower uplink
signals (777-787 MHz)
Signal leakage
Correlation or Not?
Data was simultaneously recorded whenever a leak was detected at one of the two test frequencies, 139 MHz and 735 MHz
Total number of leaks detected was 97– The examples shown here
and on the following slides are typical of what has been observed in every system evaluated
139 MHz analog 735 MHz QAM0
100
200
300
400
500
Low and high frequency leak level correlation - all
detected leaks
Fiel
d st
reng
th in
µV/
m
Correlation or Not?Leaks measureable at 139 MHz but not at 735 MHz: 13 (13%)
Leaks measureable at both 139 MHz and 735 MHz: 19 (20%)
Leaks measureable at 735 MHz but not at 139 MHz: 65 (67%)
Leakage Frequency ResponseNo leakage on Ch. 16 (135 MHz), but low-level leakage is measureable on Ch. 39 (315 MHz), Ch. 60 (441 MHz), and Ch. 110 (711 MHz)
Leakage Frequency ResponseNo leakage on Ch. 16 (135 MHz) or Ch. 39 (315 MHz), but leakage is measureable on 60 (441 MHz), and just below detection threshold on Ch. 110 (711 MHz)
Leakage Frequency ResponseLeakage on Ch. 16 (135 MHz) and Ch. 39 (315 MHz), but not on Ch. 60 (441 MHz) or Ch. 110 (711 MHz)
Examples from the FieldSources of high frequency only leaks
1
24
5
9
6
7
8
3
Summary and Recommendations
There is little or no correlation of signal leakage field strengths in the 108-137 MHz aeronautical band and at higher frequencies (e.g., 698-806 MHz LTE band)
It is critical that cable operators monitor for low frequency and high frequency leakage
Monitoring in or near the 108-137 MHz aeronautical band maintains compliance with existing FCC rules
Monitoring high frequencies provides visibility into potential problems that are unseen if only low frequencies are monitored
Benefits
Avoid cable-related interference to over-the-air services such as LTE
Ensure compliance with the harmful interference clause in §76.613
Minimize ingress from UHF broadcast TV, LTE, and other over-the-air services operating at higher frequencies
Improved plant performance and customer satisfaction
Improved visibility of points of weakness in the network
Cisco Systems, Inc.
9155 E. Nichols Ave., Ste. 400
Centennial, CO 80112
Ron Hranac Greg TresnessArcom Digital, LLC
P.O. Box 6729
Syracuse, NY 13217