Michael Graham to be on WCRN, 3 other stations

Dan.Strassberg dan.strassberg@att.net
Wed Feb 6 10:09:26 EST 2013

As a VERY rough rule of thumb, an AM station's signal strength appears to
drop off VERY roughly as the square of the distance between the transmitter
and the listening point. (In fact, more than a few things influence this
square-law relationship: soil conductivity and the station's operating
frequency are the two most important--and most often cited--influences. With
a salt-water path between transmitter and listening point, instead of a
square-law relationship, you have a nearly linear relationship between
distance and signal strength.) However, if you accept the square-law
relationship and use it judiciously, you will find that the 10 mV/m contour
lies (VERY roughly) half as far from the transmitter as the 2.5 mV/m

Applying this to WCRN, its calculated NIF (nighttime interference-free)
contour is, IIRC, 10.55 mV/m. IOW, what R-L shows for WCRN's nighttime
coverage (inner contour) is roughly twice as far from the transmitter in
Leicester as is the actual NIF contour. WCRN's real NIF may be a skosh lower
than 10.55 mV/m, however, because at least one of the major contributors is
a now-dark Canadian AM. And then there is the argument over whether an NIF
contour should be weaker than 20 times the RSS (square root of the sum of
the squares) of the interfering co-channel 10% skywaves. (I think the FCC
has added to the NIF calculation some first-adjacent-skywave value, but I am
unclear on how that term enters into the calculation. For example, does WHAS
really interfere with WCRN at night?)

Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Scott Fybush" <scott@fybush.com>
To: <boston-radio-interest@lists.BostonRadio.org>
Sent: Tuesday, February 05, 2013 11:37 PM
Subject: Re: Michael Graham to be on WCRN, 3 other stations

> On 2/5/2013 1:54 PM, Dan.Strassberg wrote:
>> On a good radio, a 2.5 mV/m daytime signal is usually listenable, as
>> long as interference from all of the stuff (fluorescent lights and light
>> dimmers,
>> for example) that raises the AM noise floor is not too severe. But 2.5
>> mV/m
>> is hardly what most people--even radio geeks--would call a strong signal.
>> The FCC considers 5 mV/m (twice the field intensity at R-L's inner
>> contour)
>> to be the minimum for service to a station's CoL.
> Experts whose opinions I trust tell me that in major markets where it's
> possible to do some fairly granular breakdowns of ratings data, the
> evidence is now clear that mass-market AM stations get essentially no
> listeners in areas where their signals are less than 10 mV/m - and that's
> rapidly edging up to 15 mV/m as "all that stuff" continues to raise the AM
> noise floor. (Stations with specialty formats still draw audiences at
> lower signal levels; if the music you want can be found only on WJIB,
> you'll make a much bigger effort to tune in 740 even if you're in an area
> where its signal is weaker.)
> If R-L showed the 15 or 10 mV/m contours, they'd be significantly smaller
> than the 2.5 mV/m "inner" contour now shown.
> s

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