The future of AM radio

Sun Feb 3 12:25:03 EST 2008

The issue would have been delivering 25 mV/m to the the CoL's "central
business district." (This was ultimately defined as the main post
office--I don't know whether that definition was operative yet in
1946, but it may have been; central business district was obviously
way too vague.) For Boston, I don't know whether the main post office
is considered to be South Postal Annex near South Station, which is
where most of the work gets done, or the granite building right near
Post Office Square. The 25 mV/m requirement was abolished in the late
1980s, I think, leaving only the requirements to cover the entire area
of the CoL with 5 mV/m by day (including CH) and 80% of the population
with an NIF signal by night. When 1510 moved to Waltham in 1981,
though, the old 25 mV/m requirement still existed, kind of forcing the
high-on-the-dial station, despite its 50 kW-U and 198-degree towers,
to locate in the undesirable spot where it landed.

Anyhow, according to V-Soft, WHDH (WEEI) delivers only about 35 mV/m
to Boston's 02101 Zip code showing that there wasn't a lot of leeway
in where the transmitter could be located. I don't know how free the
FCC was with waivers of the 25 mV/m requirement, but 1150 received
such a waiver; its signal strength in the 02101 Zip is only in the mid
teens. I think there might have been problems, though, with obtaining
such a waiver for a 50 kW station with half-wave towers
directionalizing toward its CoL.

As for WHDH becoming a IB, an idea you commented on in this thread a
couple of days ago, I believe that it was already impossible on the
day WHDH signed on. I don't know how different the formulas were back
then compared with those used today for calculating NIFs. (I suspect
that, out to a certain distance, the old formulas for estimating the
10% skywave signals that entered into the NIF calculation predicted
weaker signals than do today's formulas. Beyond that distance (no, I
don't know how many miles or kilometers it might be), the opposite may
well be true. (My reasoning is that, until maybe 15 or 20 years ago,
nobody worried much about interference from mainland stations to
Hawaiian stations. For example, sometime in the 70s or 80s, I think,
KFMB was granted 50 kW-N with a pattern that sends the equivalent of
substantially more than 100 kW straight at KGU--Hawaii's oldest
station. No way would such an upgrade be allowed today!) In any event,
the only US ex-1B that is co-channel with another ex-IB that runs ND-U
is KGO; it's about 780 miles further from WGY than WHDH was from KOA.
I suspect that the NIF calculations probably established that WHDH had
an NIF in the low 3 mV/m range--essentially all of it because of KOA.
But that means that WHDH would have had no protected nighttime-skywave
coverage--a requirement for a station to be designated a Class I. In
addition, there were large areas of the Connecticut River Valley in NH
and VT where WHDH and co-channel WXKW duked it out during the daytime.
What that means is that WHDH did not have interference-free groundwave
coverage much beyond its 0.5 mV/m contour. By day, Class I's were
supposed to be free of co-channel interference within their 0.1 mV/m
contours. (First-adjacent daytime protection extended only to 0.5 mV/m

Dan Strassberg (
eFax 1-707-215-6367

----- Original Message ----- 
From: "Martin Waters" <>
To: "Dan.Strassberg" <>;
<>; "Garrett Wollman"
Sent: Sunday, February 03, 2008 11:07 AM
Subject: Re: The future of AM radio

> --- "Dan.Strassberg" <> wrote:
> It was no secret that, because of its lower
> frequency, WLAW
> had a natural advantage in coverage. Curiously, the
> fact that WLAW was
> licensed to Lawrence but wanted to serve Boston forced
> on it a
> transmitter location and a directional pattern that
> were, for the most
> part, superior to WHDH's.
> --------------
>    Couldn't WHDH have done better by building on a
> site farther west and/or southwest of the city? That
> way, it should have done better in metro west --
> which, now that it has a substantial population, is
> the major weak spot for every old-line Boston AM
> station except WBZ.

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