[Lowfer] New Ham band

Tue, 21 Jan 2003 17:07:42 -0500

At 11:48 AM 01/21/2003 -0500, you wrote:
>Thanks for an informative reply. I learned much about PLCs from your post.
>
>Mike
>wa1ptc
>
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]]On Behalf Of [email protected]
> > Sent: Tuesday, January 21, 2003 12:04 AM
> > To: [email protected]
> > Subject: RE: [Lowfer] New Ham band
> >
> >
> > At 01:18 PM 01/20/2003 -0600, Tod - Minnesota wrote:
> > >Regretably, the power company lobbying groups
> > >have done an about face and declared that such a band could
> > cause 'homeland
> > >security' problems by hams interfering with PLC's. I suspect the real
> > >concern is that the power companies do not meet the FCC requirements for
> > >emmissions from the PLC's.
> >
> > At UTC's (Utility Telecommunications Council) look into this
> > situation last
> > fall, rather than seriously look at the facts, they just did the
> > "knee jerk"
> > response and said, "It won't work."    I had recently left this field of
> > endeavor
> > and unfortunately could not inject any serious input and my
> > former colleagues
> > mentioned this to me in passing after the session was over, saying, "Gee,
> > wish you could have been involved..."     Grrr.....   (gritting
> > of teeth!!)
> >
> > Aside from some minimal radiation (and pickup) using the 3 phase HV
> > transmission lines, it should be mentioned that PLC receiver sensitivities
> > are measured more in "volts" than microvolts.  They operate in a high
> > signal mode to stay above the "line noise" that would be a problem if
> > trying to receive microvolt type signals that we are used to working with.
> >
> > Hence, PLC xmtrs usually operate in the area of 10 - 25 watts using a
> > full length "transmission line" that has a nominal loss of 1dB or less
> > per mile.   As long as "line tuning" (Z matching 50 ohms from equipment
> > to the "hundreds of ohms" of the HV line) remains decent,  the
> > PLC receivers are impervious to any interference.   Interference, if any,
> > usually shows up when a neighboring power company fires up their
> > PLC on the same freq.  (and even this is normally coordinated thru UTC)
> >
> > Consider the minimal signal levels of Amateur/Experimental stations
> > with extremely low efficiency and they might get signal "pickup"
> > on a level quite lower than their normal ambient noise......
> > which, again, is far below their normal operating margin in the high
> > millivolt range.    Another factor of isolation would be that PLC
> > "polarity" is necessarily horizontal, and our LF radiation is
> > necessarily vertical.
> >
> > Other than that, PLC usage by utilities is at it's lowest point ever,
> > with all "intelligent" or data type modes being conveyed on Microwave
> > or Fiberoptic links.   The remaining usage consists mainly of
> > "trip blocking"
> > signals that are sent to "prevent" unnecessary tripping of
> > substation breakers
> > when a fault occurs somewhere on a HV path.   If a million to one
> > situation
> > occurred where a lowfer signal hit exactly on a PLC trip blocking receiver
> > and was of sufficient strength, it would not cause any harm, but actually
> > work "in cooperation" with the main purpose of the system..... which is
> > to PREVENT tripping!   (a PLC rcvr with NO signal present under a fault
> > condition would allow tripping of the substation breakers)    If
> > a real fault
> > occurred near a particular substation, there would be no signal conveyed
> > to the PLC rx in any manner, due to the fault (or shorting
> > condition) on the
> > HV line killing any signal pickup.
> >
> > Just so I don't leave anything out, there is another mode called "transfer
> > trip" which is used to trip breakers at a distance via PLC.
> > However, this
> > system uses two to four signals that shift apart in frequency to ensure
> > a "foolproof" system (not one single freq signal).   Also, at the point of
> > transmission of a trip signal, this system increases xmit power 10 dB.
> > No problems here either.......
> >
> > Sorry for the verbiage, but what this situation needs is some
> > intelligent FCC
> > input during any comment period....if it is still open.
> >
> > Perry      w8au
> >
> >
> >
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