[Lowfer] 1750M?

Mon, 20 May 2002 22:30:05 -0400

At 04:14 PM 05/20/2002 -0500, Bob Roehrig wrote:
>On Mon, 20 May 2002, Tod-Idaho wrote:
>
> > It is my understanding that the power
> > companies use these frequencies 'without' any specific allocation from the
> > FCC.
> > As far as I know they have no legal standing that protects them
> > from interference from FCC licensed services.
>
>You are exactly right.  Read part 15.113 and 15.5. They are NOT protected.
>
>Also, Think about the fact that GWEN operated high power stations here for
>a number of years - if they didn't cause problems why should lower powered
>ham signals?

Bob:
To add to your information......  the utilities use of PLC has diminished 
greatly over the years.
This is due to their use of Microwave networks and the now more popular 
fiberoptic networks.
The LF spectrum used by electric utilities over HV transmission lines 
spanned about 50 kHz to
300 kHz and was used for voice, telemetering, remote control, transfer trip 
circuits and substation
trip-blocking schemes.    250 kHz of spectrum for all of this is not much 
compared to a Microwave
baseband of up to 6 mHz (at 6 gHz) and the huge amounts of capacity of 
fiberoptics.

In actuality, these days, what's left on LF PLC is typically the 
non-intelligence modes of
transfer-trip and trip-blocking (called "relaying").   The voice, 
telemetering and remote control
of power plant generation has all been transferred to MW and fiber.

Also keep in mind that PLC receivers are kept at very low sensitivity to 
eliminate problems
of ambient noise that is always present on HV lines.   PLC transmitters 
typically range from 1 to 10
watts and at the general loss figure of about 1 dB per mile,  high signal 
levels are maintained
from major substation to major substation.   What this means is that 
outside interference
is almost non-existent.

Additionally,  the HV lines that PLC is conveyed on are three phase where 
the spacings
of the parallel wires are from about 6 feet to 10 feet, depending on the 
voltage.  This
corresponds to a parallel RF transmission line where radiation does not 
occur to a great
extent and conversely the reception of outside signals is greatly 
limited.   We had an
old "rule of thumb" that PLC signals could be received out to about 1/4 
mile and not
much further.....  (what the receiving system might be for that standard, 
we never knew) :-)

The GWEN system did at first provide some concern to utilities, but later 
on proved not to
be a problem.   It would not even raise an eyebrow today......

Hence, there is little valid argument from utilities.   Any comments on 
these proposals
should not give too much credence to the utilities concerns, and the more 
we are conversant
with PLC systems and usage, the better we can counter any arguments.

73,

Perry     w8au     (a 30 year veteran of utilities telecommunications...)