Changing frequencies - changing transmitters? Power?

[Garrett Wollman]

<<On Sat, 18 Nov 2006 00:24:41 -0500 (EST), Peter Murray <pete@partnercomm.com> said:

> The listenable radius of WCRB is almost indistinguishable from that of
> WKLB-FM, because the additional height under WCRB's antenna is balanced
> out by the 5.2dB of additional power for which WKLB-FM is licensed.

However, this does not take into account the differences in reception
caused by such factors as terrain (outside the 16 or 32 precise
radials used to compute HAAT), location of other transmitter sites,
and antenna design.  For some listeners, even in downtown Boston, the
99.5 transmitter site in Andover may provide superior reception to the
102.5 site in Newton due to intermodulation products from the stations
on the Prudential Tower.  Conversely, for listeners in parts of Canton
and Randolph, the shadow of the Blue Hills will impair reception of
99.5 even though the FCC's F(50,50) curves predict a good signal
there.  The experts I have spoken with agree that higher is usually
better, despite the ERP trade-off.

Those who have followed FCC FM and TV applications in the last several
years will be familiar with the Longley-Rice method, a signal
prediction algorithm that takes fine-scale terrain into account (and
also other factors such as the climate type); most of the
signal-strength maps seen in FCC applications today are generated
using this method, because it can be used to predict with much greater
accuracy and square-mile resolution the actual population which will
be served by a given signal.  (It's often seen in FM applications
involving grandfathered short-spacing, as an applicant must
demonstrate that the area of prohibited overlap is not increased.)

-GAWollman