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An analysis of the ACA report on the Country Energy BPL trial in Queanbeyan, NSW between November 2004 and March 2005.

This report is an analysis of the ACA's report on the Country Energy BPL trial in Queanbeyan, NSW between November 2004 and March 2005.

Contents

Background

The ACA published a report on 28 April 2005 entitled "ACA Field Report Country Energy BPL Trial Queanbeyan NSW - February 2005". The report is an analysis of the ACA's measurements of electromagnetic field strengths of radiation from that BPL trial. The full ACA report is available online from the ACA's website at http://www.acma.gov.au/acmainterwr/lib284/queanbeyan%20trial%20feb%202005%20final%20public%20report.pdf

Analysis

This document is an analysis of the ACA's report and extrapolation of the reported measurements to predict the impact on a typical amateur radio station with an antenna located 15m from the nearest BPL activated power conductors, and should be read in conjunction with the ACA report.

The ACA report describes the trial configuration is some detail, their measurement configuration and results of their measurements in February 2005.

In brief, the BPL trial was conducted in two precincts in Queanbeyan, one an industrial area around Hinksman Ave, and the other in a residential area around Campbell and Bruce Streets. The ACA made field strength measurements of the residential deployment in Campbell and Bruce Streets using a R&S Field Strength Meter and loop antenna designed for EMC measurements.

The key data presented that allows interpretation and extrapolation of the impact on an amateur radio station is that presented in Appendix A (pp 10-12).

The third plot in Appendix A is for Test Site 9 and shows peak field strength measurements in dBµA/m in the S plane over the frequency range of 0.15MHz to 30MHz. The frequencies used for traffic and that were observed at Test Site 9 covered the 40m, 20m, and 15m amateur bands. Table 1 extrapolates field strength measurements scaled off that plot to model the impact on an amateur radio station in a residential environment. Note that the noise floor in these plot is the internal noise of the measuring instrument and not the ambient noise (clarified by email with the ACA 06/04/2005).

The ACA's measurements were made at a distance of 3m horizontal (7.2m radial) from the nearest powerline using a field strength meter with an effective noise bandwidth of 10kHz. This extrapolation is to an antenna typical for each of the bands at a distance of 15m from the nearest BPL activated power conductors. The extrapolation factor used for modelling the distance is that power reduces as the inverse of the square of distance (which is an accurate model for a point source radiator in free space). The question of extrapolation of field strength with distance is a complex one, though power may fall more quickly in the near field, power will fall less quickly from a linear or area radiator. The error remaining is probably small compared to the excess of radiated interference over the expected ambient noise level. The industry is still working on agreement on a simple distance model.

Table 1: Extrapolation of ACA measurements to model impact on an amateur radio station in a residential environment.
Frequency Field strength Antenna gain (dBi) Antenna Factor (dB/m) Received signal level
Bandwidth 10kHz 3kHz 3kHz
Distance 7.2m 7.2m 15m 15m
Units dBµA/m dBµV/m dBm S meter dB wrt min expected ambient noise (1)
7.1 MHz 18 70 64 4 -17 -32 S9+41dB 75
14.2 MHz 0 52 46 6 -13 -54 S9+19dB 59
21.2 MHz 8 60 54 8 -11 -48 S9+25dB 68
Notes to table:
1. Minimum expected ambient noise is taken from the minimum noise level expected line of Figure 2 of ITU-R P.372-8.  Ambient noise in a residential area could be up to 20dB higher than the minimum noise level expected from that figure.
2. The measurements in this table are based on a peak detector rather than a CISPR quasi-peak detector. The error on unmodulated or lightly modulated closely spaced  OFDM carriers would be a dB or two and is insignificant.

Conclusion

The ACA's measurements of the Country Energy BPL trial at Queanbeyan, NSW in February 2005 contains detailed information that allows extrapolation of the measured data to model the impact on an amateur radio station located in a residential area if such a BPL system were deployed in that area.

Though this analysis is restricted to the impact on an amateur radio station, the radiated interference affected much more than the bands used by amateur radio, and would have impact on other radio communications services operating in or near the BPL service area.

Amateur radio operations on the three bands affected in this case are most commonly limited by the ambient noise level (rather than the internal noise of the station receiver).

The modelled received signal level of the BPL interference based on the ACA's measurements would be -32dBm (S9+41dB), -54dBm (S9+19dB) and -48dBm (S9+25dB), and  up to 75dB, 59dB and 68dB above the lowest expected ambient noise in respect of the 7MHz,  14MHz and 21MHz frequencies.

An amateur radio station located in a residential environment where a similar BPL system was deployed would not be safely able to transmit at all on the 7MHz, 14MHz, and 21MHz bands because of the high risk of interference to possibly active stations that would not be heard through the BPL interference, effectively curtailing all activity on the band by such a station.

V1.1 20/02/09 19:26:38 -0700

 


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