FCC considerations

If you read the FCC's public notice DA 11-1535, dated Sept. 13, 2011, you will note that it reads "Use of MDCL technologies requires a waiver of Section 73.1560(a) of the Commission's Rules, which sets upper and lower limits for an AM station's operating power." So get ready to ask for that waiver. Fortunately, the FCC is trying to make it as easy as it can. "AM licensees who wish to implement MDCL technology shall file with the Audio Division a letter requesting waiver of Section 73.1560(a) of the Rules..." Once the FCC has allowed the waiver, it will modify your license accordingly.

Other considerations

It's pretty clear that when measuring the common point current, base currents or monitor points you'll need to be able to turn off MDCL. What about modulation monitoring, though? Well, fortunately at least one AM modulation monitor can be using during MDCL: the Belar AMMA-2. In addition to monitoring standard AM modulation, it monitors MDCL AM transmissions. The AMMA-2 tracks the carrier, capturing the highest and lowest values of the carrier level, as well as the decibel ratio of the carrier high/low values. Modulation readings are then referenced to the carrier level appropriate for the MDCL system in use.

MDCL can be an effective means of lowering your station's overhead by reducing power bills. It should be noted that MDCL is most effective at power levels greater than 20kW. Consult with your transmitter manufacturer to see how it can potentially benefit your operation.

Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York.