Re: LPFM's I Never Thought I'd See

[Aaron Read <aread@speakeasy.net>]

At 05:19 PM 7/8/2003, Laurence Glavin wrote:
>In the past week, two LPFM's have been authorized in NH:
>an operation on 102.9 in Londonderry;  and a 94.7 in Concord.
>It seems to me that the former will operate on a channel occupied
>by a 100k blowtorch transmitting from west of Portland, and the
>latter immediately adjacent to another blowtorch from atop
>Mt. Washington.
>If both put up 100 watt C/P antennas at a decent altitude,
>it seems they will cause the kind of interference LPFM opponents warned 
>about. (I'm not anti-LPFM).
>Or are the communities so far out of the coverage area
>of the full-power stations the FCC doesn't give a rat's posterior (don't
>want to offend Peter Casey)?
>
>Laurence Glavin

No, they will not.  They will cause interference to the stations as you 
describe but only within the area immediately around the LPFM's 
transmitters and besides which - it's perfectly legal.  Londonderry is at 
the 40dBu contour of WBLM (Portland, ME - 102.9), and Concord is around the 
54dBu of WHOM (Mt.Washington, NH - 94.9).   Assuming a fairly small contour 
area for the LPFM's...a safe assumption...the interference zone is small.

Going off memory here....in the legal world, the contours don't 
matter...LPFM is strictly by distance separation, I believe.  Hence WBLM's 
and WHOM's huge contours sort of work against them here, since the 
distances are just by class....the fact that WBLM and WHOM have contours 
WAAAAAY beyond the usual range of their class is meaningless with LPFM.

In fact, a blowtorch like WHOM works to LPFM's favor in general...since 
that blowtorch will block anything else from getting too close and thus 
keeps the dial more "open".  That allows for more pipsqueak signals like 
LPFM's to squeeze in around the edges.

Remember also that LPFM is authorized for 100 watts at 30m HAAT...or the 
equivalent.  So if it's more than 30m HAAT, the wattage must be reduced 
accordingly.  A better way of thinking about it is that the service contour 
(60dBu) has a diameter of about 5.6km regardless of what the actual 
power/height are.   Obviously more height usually means better overall 
reception and less multipath - especially in hilly New Hampshire areas (I 
dunno how hilly Londonderry and Concord are, though).   But the service 
contour will remain about the same: small.  ;-)


--------------------------------------------------------------------------------------------
Aaron "Bishop" Read             aread@speakeasy.net
FriedBagels Consulting          AOL-IM: readaaron
http://www.friedbagels.com      Boston, MA