Monday, June 29, 2009

FCC "regularizes" rules for FM translators of AM stations

The FCC has released regular rules for the use of FM translators by AM stations.

Existing FM translators -- those either on the air or holding construction permits as of May 1st -- will be allowed to relay AM stations. Applicants for new translators must specify which station they plan to relay, and applications that specify AM stations will be dismissed. Existing translators must notify the FCC when they change which station they relay; if a translator authorized after May 1st notifies the FCC of intent to relay an AM station, they will be denied permission. The FCC indicates they may relax this policy after the next LPFM filing window is complete.

The 60dBu service area of such translators must be contained entirely within 25 miles of the AM towers or the 2mV/m daytime service area of the AM station, whichever is smaller. The 60dBu service area of a typical 50-watt translator (assuming an antenna 30m high) is a bit less than 5km, about 3 miles.

3 comments:

jo1723se said...

Dear,

Do you know something about AM translators, at AM BAND (Am&Am), improoving AM signal.

In older times, someone told me
about AM filler into tunnels.

Thank you.

Eduardo Cappia

Doug Smith said...

Eduardo, sorry about the delayed response!

There are no provisions in the rules in the U.S. for translators *within the AM band*.

It is legal for one AM station to broadcast the same programs as another AM station, but both stations must have a full, regular license.

There are also a few "synchronous repeaters", where an AM station has a low-powered relay *on the same frequency* as the main transmitter. These are all experimentally licensed.

Probably the best-known is a 230-watt transmitter on 770KHz in Santa Fe, New Mexico. It relays the 50,000-watt station on that frequency in Albuquerque.

The Albuquerque station is required to switch to a directional antenna at sunset, protecting a New York City station on the same frequency. But the state capitol, Santa Fe, is in the direction in which the nighttime antenna radiates particularly poorly. So the 230-watt relay transmitter provides service to Santa Fe.

Doug Smith said...

Oh, I have heard of AM fillers in tunnels. I think in most cases there is no transmitter. They just install a receiving antenna outside the tunnel, then connect it directly to a transmitting antenna *inside* the tunnel.