[BC] FM TX spacing question

[Peter Moncure]

Mark Humphrey wrote:
>FM field strength curves are based
>on an inaccurate, simplistic method that was developed in the 1940's!
>There are certainly more accurate coverage models available today (some of
>which are permitted to be applied in other services, such as land mobile and
>DTV) but the FM broadcast industry seems to be afraid to adopt them for fear
>of upsetting the good ol' "status quo".
>
The problem of creating a better "contour" is in 
fact not simple at all.  I was chair of a working 
group at TIA charged with that task among others, 
and after two years of work we basically 
concluded it was impossible.  There were some 
really good minds on that committee, too, better 
than mine for sure.  But when we tried to stretch 
the general case to include those famous sites in 
the California foothills where coverage doesn't 
really begin for 20 km. and then goes forever, we 
were stuck.  Harry Wong, of FCC's OET, came up 
with the so-called point-to-point contour, based 
on Longley-Rice, but IIRC it was AFCCE which shot 
it down.  One of the problems with a contour 
derived from any tiled study (as with 
Longley-Rice e.g.) is that somewhere or other it 
fails the test of a contour value of N+1 dB? 
being smaller at all azimuths than N.

Now, if you were to ask about the HAAT-ERP 
calculus, you're on the money.  FCC tried to 
standardize this in the infamous Docket 80-90, 
but the class B FM's got together and squished 
it, so it remains approximate (despite Dale's 
online calculator) to this day, and for no good reason.

Ask me sometime about the conversations I had 
with Gary Kalagian on the subject of HAAT if you 
want to be awash in soap.  That was another of 
the tasks of the TR 8.18 committee (to 
standardize HAAT and contour generation), which 
we IMHO did quite well, to complete apathy from 
exactly everyone.  Oh well, a little slop keeps 
the consultants going, and they have to eat too.

-- 
Peter Moncure, VP RadioSoft