Hello Iain and Group,
High Frequency Power Line Communications is a can of worms.....
Open it and you will have a lot of opposants, bystanders and supporters...
So be aware....
My opinion is a spectrum protection opposant....
As some of our collegueas already stated: roll-off with distance is very
difficult
to calulate..
At first: sources of radiation consist of magnetic sources (wires carrying
current)
and voltage sources (wires having a different potential, be it due to the
source voltage or to propagation delays)
At second: Wavelengths between 1 and 30 Mhz are anywhere between 300 meters
and 10 meters
Third : Electromagnetics define close field and far field.
the first being a rapidly decreasing (with d) magnetic or electric
:decrease 1/d^2 or 1/d^3 depending on source
the second decreasing linearly with distance.
The treshold between close field and far field is defined to be
1/(2*pi*lambda) so varies with frequency from 50 to 1m50 meters
Close fields do not propagate further then their range (compare
induction field : reinduct back into the source: no energy loss)
Far fields do get loose from the source (create energy loss) and
propagate
Fourth : measuring the E-field is not enough for PLC, one also needs to
consider close field magnetic components
as interference (and PLC receivers) do react to both E and H-field
components
Fifth : In the past a LISN was created to measure the interference capability
of unwanted emission on mains wires by measuring
the voltages on the mains connection.
The lisn attenuates differential mode signals with 6 dB and measures
common mode voltage unattenuated (V-network)
The LISN measure current contibuted interference by inserting 50
ohms and measure the voltage. Low impedance
sources may contribute more to emission than a LISN might " think"
The 6 dB attenuation was to model the "transformation" factor for mains wiring
to convert a DM to CM voltage, due
to lack of symmetry compared to an ideal twisted pair having a conversion
factor of less then 60 dB
Sixth: The LISN was found an appropriate device to control unwanted emissions
and protect the spectrum for
SPURIOUS emissions taking only a fraction of the spectrum. (their is a
statistic element in that)
Seventh : A LISN may be thought of a an appropriate device to measure PLC
interference capabilities but
when PLC devices are measured using a LISN they cannot function
decently (he he)
Eight: Manufactuers decided that a value of 6 dB for DM attenuation (Called
LCL-value) was not to favorite
for PLC designs and started (neglecting more or less aspects ) studies
showing that an LCL value of up to
20 or even 30 dB would be appropriate for standard mains wires. Using a
redesigned LISN a PLC design
could generate much more energy , having much more range and still pass the
emission tests.
Ninth: Smart modulation techniques allow for creating holes in the emission
spectrum at f.a. amateur
and broadcast frequencies. At these pre-programmed frequency slots the
emssions would be much less
then on other frequencies (although effectively reducing effectivity of the
PLC system).
Tenth: The modulation technique uses the full bandwith (but the slots) and
creates therefore statistically
much more interference then spurious harmonics from a cloick oscillator . The
designs really use the band
up to it's full extend. Resonances, that in a standard design should conicide
with a spurious frequency to create
a interference problem, will in a PLC design always occur.
Last: Using the spectrum as transfer medium for communications is already
very limited, due to a mist
of spurious radiations from PC, elevator, ignition motors and brush motors,
while all these sources
comply with the requirements. Adding an increased level (DM voltages up to 107
dBuV where mentioned)
of wideband noise makes the full AM band unusable in the presence of any PLC
system, let alone using
these frequencies for long distance communications or space exploration.
The introduction of popular called MP3-radio (small band) on medium and
shortwave will give a new impulse to the
utilization of these frequency bands and we really do not need to pollute
these with Internet data
that can be transferred much easier using twited wires, coaxes or microwave
frequencies.
PLC is not use but an abuse of the frequency spectrum.
Regards,
Gert Gremmen
Approvals manager
======================================================
ce-test, qualified testing
Member of EMC committee CENELEC/IEC
+ Independent Consultancy Services
+ Compliance Testing and Design for CE
+ Improvement of product quality and reliability
+ Testing services according to:
Electro magnetic Compatibility 89/336/EC
Electrical Safety 73/23/EC
Medical Devices 93/42/EC
Radio & Telecommunication Terminal equipment 99/5/EC
Website: www.cetest.nl (english)
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Phone : +31 10 415 24 26
Fax : +31 10 415 49 53
======================================================
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of PLC Webmaster
Sent: Monday, December 15, 2003 2:04 AM
To: [email protected]
Subject: E-field drop off with distance (1-30MHz)
I am currently researching the radiated emissions from High Frequency Power
Line Communications (1-30MHz).
I am trying to obtain information on how the e-field typically falls of with
distance. I have read books that have made claims that this is anywhere in the
rang 1/d to 1/5d. I am trying to make a statistical analysis to explain to
those who claim that in the near field it is (1/d^2) which they derive from an
infitesimally small dipole.
Does anyone know of any papers, experiments or actual EMC compliance
measurements in the range 1-30MHz that I could use to make an analysis of the
drop off rate.
Thanks,
Iain
