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Lately it seems we have been thrust into an era of change. The FM translator service, like other communications services, is no different. It has undergone some profound changes in recent months -- well sort of. As it turns out, the FM translator service, since its inception in the very early 1970s, has been subjected to several major technical overhauls.
The most recent of these overhauls came in 1990. Prior to that time, the coverage area resulting from the permissible technical parameters was quite small. Under this overhaul, the FCC started defining power in terms of effective radiated power instead of transmitter power output. The result was a maximum permissible ERP of 250W rather than the previous limits of 1W TPO east of the Mississippi and south of 40 degrees latitude in California, or 10W TPO elsewhere.
If the translator was a "fill-in", there was essentially no limitation on the center of radiation height so long as the translator did not serve to extend the primary service contour of the facility in any direction. The non fill-in facilities, such as those translating NCE stations were subject to two regionally based stair-step tables relating ERP to the center of radiation above average terrain. Intuitively this is quite sensible as it neutered the possibility of an enterprising broadcaster dropping in a translator with a coverage contour not much smaller than a full power station while bypassing the historical allocation mechanisms.
The concept of the fill-in translator became very important when the FCC finally got around to modifying the permissible service rules to allow an AM facility to be the primary station for FM translators. It should be noted that during the major 1990 rewrite, the subject of AM translators was discussed, and nixed by the FCC. Around that time significant changes to the AM technical rules were underway, and it was thought that improvements would occur in AM without the use of FM translators. Those improvements did not materialize, at least to the degree originally hoped, and the NAB, which in 1990 opposed the concept of AM translators, reversed course and submitted the petition for rulemaking resulting in the service change we see today.
The change in the rules to permit AM stations to rebroadcast via FM translators made no substantial technical changes. Rather, the modifications revolved around the permissible service sections. Because the 1mV/m contour of the translator had to wholly fit within both the 2mV/m daytime contour of the AM station to be translated and a 25-mile radius centered on that station's transmitter site, the translator would be a fill-in facility. It would therefore not be saddled with the power/height tables previously discussed, but rather would be able to utilize a maximum ERP of 250W, in most cases, as long as interference criteria and the 2/25 coverage limits were met. This is undeniably huge for licensees operating AM stations with minimal or no nighttime coverage or those with very high nighttime interference levels. With some very profound, yet simple changes, the FCC increased the value of many translators and AM stations overnight.
To avoid a takeover of all translators by AM licensees, the FCC imposed a restriction that for a translator to be eligible to rebroadcast an AM facility, it must have been authorized, either licensed or have a valid construction permit, as of May 1, 2009. Although this provision is currently being appealed, as things stand right now, the remaining pending translator applications from the 2003 filing window would not be eligible to be used for AM facilities. Assuming the appeal of this provision is not granted, a situation down the road where swaps are taking place to work around this provision is not far-fetched. Indeed we even see some shades of this right now with stations trading IBOC FM channels and the like.
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