[Lowfer] Rulemaking Ruminations - TWO: Supporting Data Needed

[JD]

Interesting results, Craig, and I believe you are correct about a 100 m 
separation being workable in many cases.  In real-world cases involving Part 
5 licensees, I gather that has been put to the test, and there have been no 
adverse effects at all, thus far.

However, I also note that the NTIA paper contains numerous plots of received 
PLC signals from power lines that are as much as 10 dB greater than 
calculated values.  In the reverse situation, transmitter into power line, 
differences tended to be more in the range of 3 to 4 dB.  I suspect it is 
these discrepancies that prompted ARRL to suggest 1 km, a separation thereby 
containing a built-in safety factor.  Particularly where trip protection 
circuits are concerned, the utilities certainly don't want us pushing the 
envelope re: S/N ratios. Workable in many or even "most" cases will not be 
sufficiently comforting to them, I expect, so a further margin is in our 
best interests as well.

Coordination might be useful where someone wants to operate at shorter 
separation distances, to ensure that no frequencies are in use by PLCs that 
would receive interference on that line.  That could open up many more 
possible operating locations in populous areas.  But I think we'll have 
trouble getting that degree of cooperation; or if we do, there'll be a lot 
of strings attached.  It's probably best to concentrate first on getting a 
separation distance in place that everyone agrees will provide the broadest 
protection, so we don't have to deal with UTC on a case-by-case basis any 
more than necessary.

As for a 100 m separation being easier to determine by visual inspection 
than 1 km, that may be true in some highly wooded, hilly places.  However, 
since it seems unlikely we'll get that short a distance in the rules, I 
don't believe visual inspection from the proposed site is going to be 
adequate anyway.

Still, it's not that difficult for an amateur to make a good determination. 
You may have to drive or hike way more than a kilometer from the desired 
operating point in some directions to fully circle the area of interest, but 
so long as you make a complete path around the area in doing so, you are 
assured of having to cross the route of any transmission line that may be 
entering or leaving that 1 km radius.  If you _do_ encounter a line, a 
Google satellite view can give you a detailed enough view of its route to 
determine its nearest point to your intended antenna location.

And, of course, for most people it'll be easier than that.  The practical 
driving distance for a closed loop around most neighborhoods (or entire 
small towns such as the one I live in) to encompass at least a circle of 1 
km radius will be on the order of 8 miles, tops.  I've known where our power 
substation is for years, and the low/medium voltage transmission line 
serving it is almost exactly one mile from me at its nearest point.  For the 
first few years I lived here, I knew even more precisely where it was...back 
then, it was directly across the street!  There was no hope of doing any LF 
here, transmitting OR receiving.

That's why I bought my farm.  From out there, I have to stand at two 
different points on diagonally opposing corners of the acreage to get 
unobstructed views of all the surrounding countryside; but when I do, I can 
see that there is nothing but a single phase distribution line within one 
mile in any direction...which my friend at the rural electric cooperative 
was glad to confirm is 7.2 kV, and is the highest voltage line you'll find 
within 4 miles of me.  That was the easiest determination anyone could ask 
for. :)

73
John