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