Field Strength Measurements Relative to ARRL Concerns Regarding BPL

1. Field Strength Measurements Relative to ARRL Concerns Regarding BPL October 16, 2003 Steve Martin Technical Research Branch Federal Communications Commission (FCC) Laboratory FCC Lab/TRB

2. ISSUES • Ambient noise levels seen by amateur antennas • Are the ITU noise models (rural, residential, etc) still valid? • NTIA Report 02-390 concluded that, at 137 MHz, • Business noise levels are unchanged • Residential noise levels have decreased • What are the noise levels near a power line? • BPL interference levels seen by amateur antennas • Distance from power line to amateur antenna: • I’ll assume 30 meters • Part 15 specifies emissions at 30 m* • 53% of hams report having antennas within 30 m of overhead power lines • Is 40 dB/decade distance extrapolation* valid? • 1 meter measurement height* vs actual amateur antenna height • Magnetic loop measurements* vs E-field sensing amateur antenna * for F < 30 MHz

3. ITU-R P.372-8 NOISE LEVELSFor a Dipole Antenna Business, Residential, & Rural curves based on 1966-1971 measurements (OT Report 74-38). Recent NTIA data shows that, at 137 MHz, the Business curve is still valid, but that Residential noise levels have decreased by 10 dB—to 4 dB below the Rural curve (NTIA Report 02-390, Dec 2001).

4. Best-Case Instrumentation Noise FloorFor FCC Lab Measurements Instrumentation noise restricts ambient noise floor measurements to frequencies > 20 MHz for typical EMI instrumentation at the FCC Laboratory Note that instrumentation noise floor may exceed that shown for passive loop and bicon if filtering is required to prevent preamp overload by radio or TV signals

5. Locations of Ambient Noise Measurements • Potomac, MD: • 2-m antenna height • Directly under power line • Local BPL disabled • In front of FCC Laboratory: • 10-m antenna height • 30-m from power lines • No BPL

6. FCC Lab Measurements of Ambient Field Strength Near Power Lines At a representative location for an amateur antenna (10m high, 30m from the power line across street from FCC lab), average noise floor for horizontal polarization is 5-8 dB below ITU Rural curve (also below preamp noise with broadband antenna)

7. FCC Lab Measurementsof Access BPL Emissions

8. 14 m slant range 11 m 11 m 10 m 30 m C AmateurAntenna 30 m slant range A B 1 m 1 m Loop Antenna at 1 m height Loop Antenna at 1 m height Actual loop antenna axis would be horizontal and parallel to the page or vertical and parallel to the page.

9. Ron Chase’s Model

10. FCC Lab Access BPL Measurements Extrapolated to Representative Amateur Antenna Location

11. Extrapolated BPL Emissions Relative to Ambient Noise Fields at Representative Amateur Antenna Position 28-dB increase in noise floor caused by BPL system operating 11 dB below the Part 209 limit in amateur band Narrowband signals in amateur band that would be swamped by BPL signal

12. Considerations for BPL NPRMWith Respect to Amateur Radio • Amateur radio versus robust system (e.g., public safety?) • A robust system is designed to operate in near-worst case noise fields • Amateurs (and shortwave DXers) operate close to the local noise floor to maximize com distance. Some amateurs choose their house locations based on low radio noise levels. • BPL versus other Part 15 devices • BPL devices radiate at or near the Part 15 limits across a broad range of frequencies. • Achieving throughput and range requires broadband signal injection at as close to the emission limits as possible • Two of three access BPL systems measured by the FCC Lab emitted at the Part 15 limits • Except for BPL, it is unlikely that an amateur will be exposed to a Part 15 device near his property line that radiates at or near the Part 15 limits in an amateur band. • Except for BPL, radiation from a Part 15 device in a neighbor’s home will likely be attenuated by walls before reaching an amateur’s antenna. • FCC measurements and predictions • Emissions from a BPL device operating 11 dB below the Part 15 limit are predicted to exceed by 27 dB the ambient noise floor 30 m from a power line at the FCC Lab’s “Residential” location. • That BPL system showed no reduction in radiated emissions 200 m downline from the coupler • Conclusion: • BPL operating near the current FCC limits without specific means to reduce emissions in amateur bands will likely have a major impact on some amateurs. A 25-35 dB increase in noise floor 30 m from a residential power line is significant—especially if decay rate down the line is low. • The FCC should make power companies and BPL manufacturers aware of the high likelihood of interference • “PPL officials said the shortwave operators shouldn't be affected. If there was the potential for a problem, the Federal Communications Commission, which regulates radio frequencies, wouldn't have given the company the green light on commercializing the service, they said.”