another look at signal leakage...there is little or no correlation of signal leakage field strengths...
Post on 29-Mar-2020
1 Views
Preview:
TRANSCRIPT
Another Look at Signal Leakage: The Need to Monitor at Low and High
Frequencies
Ron Hranac
Technical Leader
Cisco Systems, Inc.
Greg Tresness President
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 30
Over 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 example
Verizon 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
0
100
200
300
400
500
139 MHz analog 735 MHz QAM
Fie
ld s
tre
ngt
h in
µV
/m
Low and high frequency leak level correlation - all
detected leaks
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 Response
No 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 Response
No 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 Response
Leakage 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 Field Sources of high frequency only leaks
1
2 4
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
rhranacj@cisco.com
Ron Hranac Greg Tresness
Arcom Digital, LLC
P.O. Box 6729
Syracuse, NY 13217
tresness.greg@arcomlabs.com
top related