R & L Media Systems


Beware Of Interference   Updated 1/28/2023

   It a beautiful day in Nashville. You bought a construction permit on channel 36, 1,000 Watts ERP, non-directional, covering almost 500,000 people in the 80 dBu contour for $25,000. The seller did sell it based on no refund, but you had an FCC Construction Permit, so what could go wrong.

   When you arrive at the tower site, on the side of the transmitter box, you find a hand written note. "You do know there is a full-power on channel 36 on the same tower, right?"

   But how could that be? You have a Construction Permit from the FCC. There must be a mistake! But there isn't. When you apply for a channel, the FCC is concerned about YOUR application causing interference to OTHER stations, not how much interference YOU will receive. If you had run an FCC study, you would have found you are going to receive 92.8% interference from the full-power. If anyone complains about you causing them interference anywhere, it is up to you to fix the problem. And since there is no new interference, the FCC is not going to let you change channels.

   Far fetched? Not at all. Ran into almost the same problem with a small station.

   On the left, the FCC granted them a construction permit and license for 7,000 watts ERP and a HAAT of 118m. Their 80 dBu covered 157,334 on paper. But on the right, a 2nd LPTV station covered most of the small stations coverage and the 2nd station was there first, so they were protected. The FCC computer worried about interference from the small station to the 2nd one, not the interference the 2nd station was going to cause the small station. When all was calculated, the small station covered a grand total of 9,766 people interference free in their 80 dBu contour.
   But all is not lost. If they will turn their back to the interfering station and aim their pattern to 240 degrees and widen it, they will cover 5 times more people in their 80 dBu coverage and be the big fish in the small pond, the ideal situation for an LPTV station.
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