[Lowfer] New MW Allocation in the U.S. & Questions about LF

[w8au at sssnet.com]

At 05:40 PM 2/15/2012, craig wasson wrote:
>More likely the power companies' opposition to the LW allocation was
>the power companies control generation and switching
>using carriers in the 135khz range.  Simple on/off keying with no
>security of any kind.  So a random signal in that range might shut
>down a power plant or feeder.
>
>You would think that in this day and age they would want the power
>grid to be more secure.

Actually "security" was/is not a problem.

A similar discussion on this topic occurred over 5 years ago with a debunking
of Power Industry claims.   But it's hard for government to ignore the UTC
(Utilities Telecommunications Council) speaking as if their arguments 
were true.

The Utility use of LF is nowhere as extensive as it was years ago 
before Microwave
and then Fiber Optics mediums were used.  All voice comms, generation control
(of power plants), telemetering and data are gone. The migration from 
LF to Microwave
and Fiberoptics was due to the much greater bandwidth available. 
Power company use
of the LF spetrum is from 50 - 300 khz at most, and only provides 250 
kHz bandwidth.
What basically is left on PLC is called Protective Relaying and 
Transfer Trip.
These are non-intelligent single or dual carrier transmissions.

Protective Relaying is used all along a string of connected 
substations to eliminate the
tripping of every breaker along the path when an overcurrent fault 
occurs.  When a fault
does occur, all substations (and generator plants) send a single 
carrier to each station
to which they are connected.  The lines that are not at fault will 
convey the RF between
stations and tripping will be blocked.  The only line that will not 
be blocked is the
section that has the fault and it's RF signal will be lost because of 
the fault and will allow
the associated breakers to trip, thereby keeping consumer power 
outages contained
within a small area instead of the whole region.

Let me add here that PLC (power line carrier) receivers are not 
sensitive!  They are
designed to take volts, not microvolts, to activate them.  This is 
because sensitive
receivers would overload on the noise levels usually found on HV 
transmission lines.
The typical low loss of 1 dB per mile on HV transmission lines then 
allows PLC transmitters
to run anywhere from 1 to 10 watts with volts to spare at the 
receiving end. .

The general rule is that one should not hear a PLC signal beyond 1/4 
mile because
the 3 phase parallel lines that are used to conduct these signals 
effectively suppress
radiation, very similar to our open wire feedlines.   So, conversely, 
incoming signals
from radiated sources will not normally be picked up by these lines.

AND, even if they were, and the PLC receivers were activated, nothing 
would happen.
As stated above, this would act to prevent any tripping of breakers, 
not cause it.

Transfer Trip is a dual signal that runs continuously between major 
power plants and
major substations.  (345kV - 750kV lines)   These signals are spaced 
a number of kHz
apart and are used to actually trip breakers, not prevent it.  When 
one area has a fault
the two signals are shifted 1 kHz in opposite directions.  For 
instance the lower of the
two signals will shift 1 kHz low and the higher signal will shift 
1kHz high.  This provides
the security.  An interfering signal will never duplicate this.  AND 
the transmitters doing
the freq shifting will elevate their power levels by as much as 10dB 
just to make sure they
are received at the other end.

Again, coupled with PLC rcvr insensitivity and higher Transfer Trip 
xmtr power, the security
is maintained.

So, call it Turf Wars, or Politics.... it definitely isn't common sense.

Perry  w8au   (First Energy Corp, ret)


>On 2/15/12, KD7JYK DM09 <kd7jyk at earthlink.net> wrote:
> > : Can someone refresh my memory on what the objection within the US is to
> > : the WARC 07 allocation at 135.7-135.8?
> >
> > Wasn't it due to a lack of  kickbacks to shut up the power companies and
> > their lobbyists that know nothing about radio?
> >
> > Kurt