Re:WGBH

["Aaron 'Bishop' Read" <aread@speakeasy.net>]

At 05:08 PM 6/10/2002, dan.strassberg@att.net wrote:
>Are you sure that already granted CPs are affected by
>the freeze? I kinda doubt it. Also, are you sure that
>this particular combination of greater antenna height
>and lower power yields the same contours as the current
>operation? Not only do I kinda doubt that, I think it's
>flat-out impossible.

Is WGBH's move already granted?  I thought it was still pending...the 
freeze has been in place for several years now.  To answer your question, I 
believe CP's are not frozen.

I couldn't tell you off the top of my head whether the contours will be the 
same.  I could if the power was staying the same and/or going up and the 
Height AGL was going up, too.  But with a lower power and a higher 
HAAT...I'd have to run the math.  I would strongly suspect that the contour 
is staying the same - or close to it - because if it weren't every station 
on 90.3, 90.1, 89.9, 89.5, 89.3 and 89.1 for 75 miles would've fought it 
tooth and nail and virtually no station on those freqs that're within 
WGBH's interfering contours is terribly powerful and cannot afford to lose 
any coverage.   The only way their contour would change is if it is getting 
*smaller* - unlikely WGBH would accept such a move unless A: the loss was 
mostly in the Cape area, where their Cape stations cover well enough 
anyway, *AND* B: the greater height means better reception in the city 
and/or the MetroWest area (rich donors in Newton & Wellesley :-)

Height is always king in FM.  With greater height comes far better reach 
into terrain both natural and concrete.  Anything over 2 or 3kW will 
usually get you pretty far out in terms of distance as long as your height 
is up enough.  If you have to choose between power and height - you almost 
always go for the extra height.  It has made all the difference for WMBR, 
WERS and WBUR - just to name a few off the top of my head.

>As far as I know, the predicted contours (though not the
>real ones) for nondirectional FMs are circular with the
>center of the circle being at the TX site. I guess it
>should be possible to predict contours that show the
>effects of topography, but I believe that the HAAT is
>assumed to apply along all radials. In this case, the
>land is flat enough that, even if topography were
>factored in, you couldn't make the contours come out the
>same without using a DA.
>
>My guess is that you got your info from the famously
>inaccurate Radio-info.com. If that's where the info came
>from, we've got all the info we need on why we shouldn't
>believe your post.

Radio-locator.com is 100% accurate (within the limits of the FCC 
databases...the FM one is a lot better these days, AM still needs work) in 
their contour maps.  It's EXTREMELY important here to remember that 
contours are a basis for determining spectrum allocation.  They are NOT a 
means of gauging reception of any given station...well, in the thinnest 
sense they are but they should NEVER be counted on to determine 
reception.  HAAT is measured out over a IIRC 10 mile radius...a very flat 
area with one big hill will yield a nominal HAAT that's actually quite 
skewed in real-world terms.

For that matter, contours are 50,50 - meaning that 50% of the listeners 
will receive interference (to the point of making it unlistenable) 50% of 
the time.  So by their own definition a contour is showing an area where 
you're not going to get reception half the time.

You can indeed predict reception quite well using longley-rice calculations 
and a good terrain TOPO map...we do it all the time at Broadcast Signal 
Lab.  I think the software is pretty specialized and expensive, 
though...and it will only yield signal strength comparisons (i.e. signal A 
is 20dB stronger than signal B everywhere on the map marked in yellow, etc 
etc).   Without knowing how sensitive your receiver is - and there's some 
serious variation in receiver sensitivity out in the market - the info is 
not all that useful fro anything beyond rough estimations.


______________________________________________
Aaron "Bishop" Read       aread@speakeasy.net
Fried Bagels Consulting   www.friedbagels.com
34 Kirkwood Rd. / Boston, MA / 02135 (as of 6/1/02)