ARRL

BPL Seriously Degraded by Nearby Radio Transmitters

Introduction

Many, if not all, of the BPL designs that have been deployed to date suffer from a number of technological weaknesses. Perhaps the most critical of these is that BPL is seriously degraded by nearby transmissions from low-powered transmitters from sources like Amateur Radio or CB. In several BPL cities, amateurs have done experimentation that shows that as little as 5 watts of power from a nearby radio transmitter can seriously degrade the performance of BPL. In some cases, the interference logged off a BPL user, requiring a reconnection to the network.

This fatal flaw will seriously limit the way that BPL can be deployed and will decrease the reliability of a BPL system in any area where it is possible that nearby radio transmitters could be operating. Under the FCC's rules, BPL is an unlicensed device that must accept any interference caused to it by authorized radio services. In the past, and through decades of experience, such interference is rare to other broadband services, such as DSL, cable or satellite. However, in all of the BPL areas tested for susceptibility so far, the unshielded wiring that is used by BPL apparently picks up nearby radio transmitters and overload or otherwise degraded the performance of the system. Although this has been seen at power levels as low as 5 watts from Amateur Radio transmitters, Amateur Radio transmitters can use as much as 1500 watts of power, greatly extending area over which BPL will be unable to tune out these over-the-air signals.

Interference Studies

The following studies have been done that demonstrate that BPL systems will experience significant interference from nearby radio transmitters:

AMRAD Test of BPL Susceptibility to HF Radio Signals
AMRAD wanted to see if the BPL system in Potomac, MD was susceptible to RF in the HF band. They suspected it might be since the BPL system used portions of the HF band for its own signaling. Because of this the BPL system cannot reject this kind of interference with RF filters. Instead, the BPL system must rely on internal signal processing to reject in-band interference. An HF mobile rig was desired. AMRAD enlisted the help of Brian Cochran, WC4J and his HF mobile rig to conduct testing. This mobile rig consisted of an ICOM IC-706 Mk-IIG with a Predator 4 inch screwdriver antenna by N9JMX. A power amplifier was available for generating higher signal levels but was not needed during the testing. The tests demonstrated that the BPL system totally ceased to transfer data while the mobile station was transmitting with less than 4 watts from the curb of the susceptible house and with 100 watts from over one half mile away.

Hobart, Tasmania, Australia
A team has performed a small scale ingress test on a Mitsubishi DS2 based system in Hobart, Tasmania (Australia). The tests revealed that BPL system is severely disrupted by ingress of low intensity Radio Frequency energy from nearby radio transmitters. Less than 5W transmitter output power from a modest mobile station (estimated <1W EIRP) within 60 to 80 metres of the user modem adversely affected the BPL service.
The full report is at: http://reast.asn.au/vk7bplwatch.php#rfsusceptibility

Manassas, VA
The BPL system in Manassas, VA is manufactured by Main.net. The equipment is being operated by the local City of Manassas municipal-owned electric utility, in partnership with ComTek (Communications Technologies). In this study, licensed Amateur Radio operators in Manassas performed controlled experiments that show that even in an neighborhood that had been "notched" to protect Amateur Radio from interference, as little as 2 watts of transmitter power connected to an inefficient mobile antenna caused the system to lock up. The summary of the findings of the Manassas Amateur operators states, "By far the most devastating engineering mistake made by the BPL equipment manufacturers was not providing a means for filtering external RF from entering their system. This is a major engineering flaw with devastating consequences!"

Engineering Studies

Interference to PLC systems from Amateur Radio Operation

The Amateur Radio Research and Development club (http://www.amrad.org) has done studies in the Potomac, MD area that show the BPL systems can be made non-functional by nearby radio transmitters. See http://gullfoss2.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6515383154. Analysis by Ed Hare, W1RFI.
This study shows the calculated expected field strength from HF stations operating in the Amateur Radio Service.

 

Links to operating parameters of Amateur Radio Stations
This paper shows the power levels, frequencies, antenna gain and operating modes in common use by stations operating in the Amateur Radio Service.