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Absolute-maximum limits defined in Part 15 |
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Carrier-current must meet limits for intentional
emitters |
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Non-interference stipulated in Part 15 |
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Verified as described in Part 15 |
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Must use good engineering practice as required
by Part 15 |
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Manufacturer responsible for FCC authorization
and maximum limits |
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Operator responsible for harmful interference |
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Both are important to mitigate possible harmful
interference |
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Sec 15.209 |
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1.705-30.0 MHz -- 30 mV/m at 30 meters |
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Peak signal, 9 kHz bandwidth for measurements
made below 30 MHz |
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These limits should protect users of the
spectrum against interference, yes? |
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If the absolute emissions limits were set to
offer unconditional protection to all radio services, the permitted levels
would be unworkably low |
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Amateur Radio Service, by design, uses sensitive
equipment and weak signals |
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The “legal limit” will result in a strong signal
to nearby amateur HF installations |
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On 3.5 MHz, a half-wave dipole placed in a 30 mV/m field will receive a
–86.4 dBW signal (338 mV across 50 ohms) |
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To amateurs, this is S9+16 dB – clearly harmful
interference to typical amateur communications! |
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Harmful interference at even greater distances
than the compliance distance is likely |
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The absolute limits are not enough to prevent
interference to nearby receivers |
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Defined as the repeated disruption of radio
communications or any disruption of certain emergency communications
services |
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Merely hearing a signal is NOT harmful
interference |
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30 mV/m at 30 m works to a degree for discrete
frequency signals |
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If from broadband device, however, will
interfere with entire band(s)! |
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30 mV/m works to a degree for isolated point
sources |
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If from PLC, level will occur for entire length
of line in areas where access PLC is deployed! |
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What amateur operator has not looked at the
power lines and thought that they would make a great long-wire antenna? |
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Overhead electrical wiring spaced 5 to 10 feet
or so, far enough apart to function as an antenna |
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Building wiring has unknown loads and open light
switches that create more antennas |
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Interference will occur at a strong level over
tens of MHz, for most of entire neighborhoods or cities where PLC with
overhead lines is deployed |
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PLC performance with underground wiring can’t be
easily calculated, so this is best measured in field trials |
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FCC asking how BPL should be regulated |
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Industry wants to increase limits |
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Present limits already too high |
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ARRL has filed extensive technical comments! |
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ARRL has worked on related issues for years:
HomePlug, Home Phone Networking Alliance, VDSL |
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120 page FCC comment filing |
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Contained antenna modeling and calculations of
interference potential |
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EZNEC 3.1 used to model 300 feet of simple
electrical wiring (uses NEC-4, written by Lawrence Livermore National
Laboratories) |
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Terminated in 50 ohms – j 50 |
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Showed “gain” of –16 dBi to –7.8 dBi when over
average ground |
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Real-world installations – bigger radiators, but
more loads on line |
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Real world - multiple signals |
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Real world – open light switches? |
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Power companies have shown spotty compliance at
correcting power-line noise… |
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100 page filing |
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Contained calculations of conducted emissions
that show that the industry wants to have conducted signals up to 58.5 dB
higher than the present conducted emissions limits |
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That is a power factor of 700,000 |
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Contained an analysis of the degradation of HF
Communications by Part-15-level signals |
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Over 70 dB increase in peak local noise – on
entire length of line – in entire neighborhoods! This is from a single PLC
signal on an overhead power line line… |
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Multiple signals: 10 signals will have at least
10 dB increase – possibly more on peaks, depending on how they add up |
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Other losses might reduce the radiation
potential of line |
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Building wiring also involved – could add or
subtract loss |
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Japanese and Dutch measured studies showed
similar results to ARRL calculations |
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-50 dBm/Hz |
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+10log(3000 Hz) = +34.8 dB |
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-20 dBi |
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100,000 PLC users within several hundred miles
of a particular location? |
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+50 dB for 100,000 signals |
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Total = -50 + 34.8 – 20 + 50 = +14.8 dBm EIRP |
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+14.8 dBm PEP in every 3000 Hz from 2 to 15 (or
more) MHz! |
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If 1,000,000 signals, PEP = 24.8 dBm EIRP peak |
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W1RFI has made contact with all 50 US states and
all continents with power of +24 dBm and contact with 30 states with +10
dBm… |
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Wireless modem jacks are carrier-current devices
that use residential electrical wiring to couple modem signals between a
computer and a remote telephone connection |
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Phonex model PX-421 designed to operate on 3.53
MHz |
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These were purchased in volume by TCI Cable (now
AT&T) and installed in
conjunction with their digital cable systems |
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Widespread S9++ levels signals and harmful
interference |
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One aeronautical facility in California had to abandon its facility because of
interference from these devices |
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Phonex responded promptly, redesigned product |
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AT&T still in midst of system-wide recall!
Costs? |
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This case history demonstrates that
carrier-current devices can cause widespread harmful interference if
deployed under present rules |
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PX-421 has not been manufactured for several
years. The current Phonex wireless modem products do not pose a significant
interference potential to amateur radio |
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http://www.arrl.org/tis/info/HTML/plc |
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http://www.arrl.org/tis/info/part15.html |
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Notes