'Split-Level' Combining Explored - Radio World

'Split-Level' Combining Explored

Harris, Cox Tout Approach for Power and Space Benefits; CPB Reviews Grants
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Harris, Cox Tout Approach for Power and Space Benefits; CPB Reviews Grants

Cox Radio's Steve Fluker, director of engineering of Orlando's WMMO, and Harris Principal Electrical Engineer George Cabrera have invented what they are calling "split-level combining" for HD Radio. Patents are pending on the methodology.

At the NPR Public Radio Engineering Conference in Las Vegas preceding NAB2004, Fluker said initial tests conducted before the convention indicated the implementation scheme showed promise for helping stations to save on operation costs and equipment space needs when they go digital.

In tests conducted on April 15, Fluker said he used a Harris HT-5 analog transmitter plus a Harris Z Series-16 for the digital signal. The scheme uses a hybrid IBOC/FM signal in the auxiliary transmitter. By passing some of the analog signal through the auxiliary IBOC transmitter, combiner losses are reduced and the existing analog transmitter can still be used, he said.

His station TPO is 7.3 kW and the IBOC power level was 73 watts. That compares to traditional high-level combining of 8.5 kW for the analog transmitter and 85 watts for the digital transmitter, with both signals being fed to a high-level combiner.

Fluker said he did not need to apply for an STA from the FCC for this combining method. A standard 3 dB combiner was used.

With the split-level combining, he said, rather than sending 90 percent of the digital power and 10 percent of the analog into a dummy load, less power is wasted. He said a station's overall power consumption could be 5 to 25 percent less than with high-level combining. He and Harris said the scheme can trim power consumption and cooling costs.

Harris representatives answered questions from numerous engineers at the show. Harris Vice President of Advanced Product Development Geoff Mendenhall said that, with this implementation, "The analog transmitter is no longer required to operate at higher-than-normal power levels to offset high-level combining losses. This eliminates the need for a station to upgrade the existing analog transmitter."

A station also may use its existing transmission line and antenna system to radiate identical digital and analog signals, he said.

"Stations without floor space to add an IBOC transmitter can use the space occupied by their current backup transmitter for IBOC."

WFMT(FM) Chief Engineer Gordon Carter said the method potentially could save his station half a million dollars a year.

Corporation for Public Broadcasting representatives at the show said they would now review recent grant awards totaling more than $5 million to help 76 stations go digital. They want to see if this new implementation, plus the FCC's recent authorization of dual antennas, saves these stations in their conversion costs. If so, grant money could possibly go to more stations than originally announced, CPB said.

Asked for reaction, Broadcast Electronics Vice President of RF Systems Tim Bealor said, "It may be appropriate for some stations." However, he cautioned, "It presents a different set of problems because now you've doubled the power output into the digital transmitter. The question is, will it save stations money?"

This story originally appeared in the NAB Daily News and is (c)NAB.

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