[BC]a question for the CFR experts

[Tom Taggart]

Jason Russell asked:

"Isn't it spec'd in the CFR that it is indeed patently illegal to
intentionally attempt to communicate by commercial radio communication with
parties beyond your licensed contour..? (Or some fancy language version of
that...)"


Nope, nada, nich, nyet,non..

Contours are specified in the CFR for several reasons:

1.  For allocation purposes.  Contours, either predicted or measured, are  
used to determine if a new station, or a modified system would cause  
interference to existing authorizations by overlapping with certain  
contours of those exilsting stations.

2.  To determine if a new station, or a modified authorization meets  
minimum coverage requirements of the city of license. (e.g. coverage by a  
5 mv/m AM signal or 70 dbu FM signal)

3.  For purposes of ascertainment, usually using the 1 mv contour to  
determine the "community" covered by a station and hence the area within  
which the station must provide a service to the public and demonstrate  
that its programing covers issues of importance or interest to this  
community.

4.  For cross-ownership purposes, where the market size is determined by  
the number of city grade signals that overlap with the stations that are  
to be acquired.  (Superceded by a different test now in the metro counties  
of rated markets)

If you've followed the "DX Test" thread, its obvious that if you  
accidentally left your daytime AM station on overnight, it might not be  
very wise to respond to requests for QSL cards.  However, if you are  
operating legally, and propogation conditions allow some DX'er to make a  
rare catch, there is certainly no law preventing you from responding.  
Indeed, especially if the listener is a teenager, why not respond,  
explaining why he heard your station, what kind of equipment you are  
using, and other distant locations you've been heard in.  With most kids  
ignoring radio in favor of computers and I-pods, we need new people  
interested in this business.

AM: We all know AM will go long distances at night, even with a little  
power.  DX'ers have always looked for daytimers on winter evenings just  
before sunset.  Here in the midwest, I've heard a number of east-coast  
daytimers over the years come booming in around 4 in the afternoon, just  
before their sunset. On the other side of the coin, when I owned a  
daytimer on 1570, I remembered being 15 miles away from the tower at 9 in  
the morning listening to another station in Alabama.  It's not  
intereference, just physics.

Of course, nowadays, theree are so many stations with some kind of  
nighttime authorizations that many channels are nothing but a jumble at  
night.  But stranges conditions may make for interesting DX.  I remember  
about a year ago or so, with a low in the sunspot cycle, I picked up some  
low power stations in Florida that suddenly emerged from the usual jumble  
one night; while some of the normal powerhouse clears vanished from the  
dial.

FM:  The basic tool for predicting coverage on FM is the Commission's  
50/50 chart, which is based on  a series of measurements made long ago  
creating a set of curves based on an antenna 30 feet above ground.  It is  
called the 50/50 chart because it represents signal strengths for given  
powers/ahaat at "50% of the receiver locations 50% of the time."  So if  
the 50/50 chart predicts that your Class A station should have a 60 dbu  
signal 17 miles out from your transmitter, if you went out to that point  
with an FIM, popped your antenna up 30 feet, you might find 1 mv/m signal.  
Or 1.5 mv/m. Or .75 m/v. And, like Ohio weather, if you didn't like what  
you saw, you could just wait a few minutes and the reading would change.

Hence your FM station's "contours" are nothing more than "best guesses."

Ducting and Sporadic E are natural phenomena affecting VHF, just as the  
night to day cycle affects medium wave propagation.
A friend of mine and former business partner in my FM station has caught  
FM stations from all over the country from a short tower in his backyard.  
Including a Class D station out in South Dakota, or Iowa somewhere. Again,  
if your FM comes crashing down on another station for an hour or two  
because of ducting, it is technically not interference, but something we  
live with as FM broadcasters.
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