Air America's night signal

Dan Strassberg
Wed Jan 5 07:00:30 EST 2005

NIF = Nighttime interference free. As best I've been able to determine, the
NIF contour is figured as follows: Take the RSS (root-sum-squared, which
means square root of the sum of the squares) of the co-channel 10% skywaves
(a station's 10% skywave is the field intensity that its nighttime skywave
signal exceeds at a specified location at least 10% of the time), then drop
out all of the interfering signals that are less than 25% of the largest 10%
skywave (because, when you sum the squares of a goup of numbers, the
quantities that are less than 1/4 of the largest number each become less
than 1/16 of the largest square). The result is the 25%-exclusion 10% RSS.
Next, increase this value by 12 dB (dB = decibels--a logarithmic measure of
ratios). If you're measuring volts--as in this case--12 dB = a ratio of 4:1.
Next you repeat this excercise for both of the first-adjacent-channel 10%
skywaves, except that you increase the resulting numbers by not by 12 dB but
by 6 dB--a factor of 2. To finally get the NIF, you take the largest of the
three numbers (co channel and both first-adjacent channel 25%-exclusion

Now if you are figuring the NIF of a station in certain-other Western
Hemisphere countries (Canada, for instance), you use the 50%-exclusion 10%
RSS instead of the 25%-exclusion value to calculate the co-channel RSS. I
don't know which exclusion you use on the first-adjacent-channel values. Why
50% instead of 25%? Because the calculations are defined that way in
treaties with the various countries.

Oh, until sometime in the 80s, the NIF calaculation involved only the
co-channel interfering signals, but, in fact, even without HD Radio, the
interference from first-adjacent stations can be quite annoying. Perhaps the
best example is WWZN/ Both WWKB and WTOP deliver very strong signals to this
area. Most likely, WWZN's NIF is determined by one of these stations and not
by co-channel stations.

Dan Strassberg,
eFax 707-215-6367

----- Original Message -----
From: "A. Joseph Ross" <>
To: <>
Sent: Wednesday, January 05, 2005 12:32 AM
Subject: RE: Air America's night signal

> What does NIF mean?
> --
> A. Joseph Ross, J.D.                           617.367.0468
>  15 Court Square, Suite 210       
> Boston, MA 02108-2503          

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