How a translator can move a hundred miles without a major modification to its license.

I often write about translators that are endlessly creeping from one destination to the other.  It's a game to figure out their ultimate final resting place.  Sometimes I get it right, sometimes I get it wrong.  But how do these translators manage to move so far when it can take years from other stations to make major changes to their licensed facilities?  The answer lies in what constitutes a "minor change" to a translator license.

The FCC determines the coverage of all FM and TV stations by a protected contour.  For FM, this is the theoretical 60 dBu contour line.  It takes into effect antenna height, transmitting power, directional antenna patterns if necessary but not terrain.  For a translator to make a minor modification to its license to move elsewhere, the 60 dBu contour must overlap the current contour.  In other words, there has to be a small area of overlapping coverage for the move to still be considered "minor".  This leads translators, which are limited to 250 watts of power, to little leaps from permit to permit.

It's these "overlapping hops" that have allowed translators like W286AQ to move to so far from home.  The station started off near Northport in Tuscaloosa County, but moved, one overlapping hop at a time, all the way to Lay Lake in Chilton County.  If I remember correctly, it's been four or five "hops" from Northport to Chilton County.

Along the way, sometimes these translators will bump up into a licensed full power station's coverage area.  They can't be granted a license if they are interfering with a full power station, as they take higher priority than translators (or LPFM stations).  The solution is to change frequencies. But only certain frequency changes can be made for it to be considered a minor modification to a license by the FCC.  These are 1, 2, 3, 53 and 54 channels up or down.  This equates to moving to a first-, second- or third-adjacent from the current frequency, or moving 10.6 or 10.8 MHz over.

Using W286AQ on 105.1 MHz again as an example, here are the alternate channels the station could move to without requiring a major modification to it's license:

• 104.5 (3rd adjacent)
• 104.7 (2nd adjacent)
• 104.9 (1st adjacent)
• ** 105.1 **
• 105.3 (1st adjacent)
• 105.5 (2nd adjacent)
• 105.7 (3rd adjacent) 
• 94.5 (down 53 channels)
• 94.3 (down 54 channels)

That's not to say that W286AQ could move to any of these channels, but it's an idea of what the FCC would consider.

So the next time you see a translator making what seems like inconsequentially small moves in frequency or transmit location, you'll know why — they're gaming the rules to move to a more lucrative area.