[Lowfer] New Ham band

Tue, 21 Jan 2003 11:48:25 -0500

Perry:

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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