Harris Broadcast and WOR(AM) say
they’ve had success with a power-saving Modulation-Dependent Carrier Level
algorithm at WOR, with no effect on Arbitron Portable People Meter data
encoding/decoding, HD Radio signal coverage or digital audio quality.
meter reading of about 38 kW is the approximate average power level reading of
a 50 kW transmitter after the AMC (–3 dB) MDCL algorithm was turned on.
Normally the meter would read 50 kW.
MDCL algorithms have been used by
broadcasters operating high-powered AM transmitters in Europe for a number of
control algorithms for AM transmitters enable stations to save money on
operating costs by reducing the carrier without reducing overall transmitter
power. Recently the FCC began allowing AMs to use the
power-saving technology on a waiver basis.
According to Harris Broadcast Vice
President of Transmission Research & Technology Geoff Mendenhall, the
commission is taking a case-by-case approach to waiving the rule that a station
must maintain authorized power levels. He said the agency doesn’t want to
encourage struggling AMs that might otherwise be tempted to try to save money
by lowering power and reducing coverage, as an alternative to going dark.
Harris engineers worked with Tom Ray,
corporate director of engineering at Buckley Broadcasting/WOR(AM) in New York,
to test the compatibility of two Harris MDCL algorithms.
Engineers tested Harris algorithms for Amplitude
Modulation Companding (AMC) with a carrier reduction level of 3 dB at peak
modulation, and Adaptive Carrier Control (ACC) at carrier reductions of 2dB,
3dB and 6dB at minimum modulation. AMC reduces the carrier level during
segments when modulation levels are high; ACC reduces the carrier level during
segments when audio modulation levels are low.ACC plus reduces the
carrier level during segments when audio modulation levels are low, while AMC
plus reduces the carrier level during segments when modulation levels are
WOR at 710 kHz is 50 kW both day and
night, and uses a pair of Harris 3DX-50 transmitters feeding a three-tower
directional antenna array. It had the MDCL option installed on both
transmitters. The station’s programming is mostly talk radio with moderately to
heavily processed audio.
Through testing that began in late
November, participants found that AMC was the most compatible with simultaneous
HD Radio operation, causing no noticeable change in HD Radio coverage,
according to Harris and WOR. AMC also provided the largest reduction in
transmitter power consumption, by saving 37 percent in average AC power input
to the transmitter.
Fluke 434 power quality analyzer was used to measure the actual total AC power
consumption of the transmitter with and without MDCL applied. The Sony
ICF-SW7600 portable receiver was one of the receivers used to check for audio
quality and coverage with the MDCL switched on and off.
Ray estimated this translates up to a
$3,000 per month savings on the electric bill at his New Jersey transmitter
site. As RW has reported, Nautel, another MDCL proponent, has estimated that a
50 kW AM transmitter running 24/7 could easily save $20,000 a year or more,
based on modest electricity rates of 10 cents per kilowatt hour.
Testing MDCL compatibility with PPM was
vital, Mendenhall said. That’s because if a station’s PPM encoding is impaired,
the station doesn’t get listening credit while the encoding is not working.
During testing, WOR called the Arbitron
PPM monitoring station in New York, which assured the station the PPM
encoding/decoding was not affected by the power-saving technology, according to
Ray and Mendenhall.
AMC remains on the air at WOR and Ray
intends to keep it operating. During testing, the AMC was shut off every three
hours so personnel could take carrier power measurements. Ray said WOR’s
carrier is only running at around 26 kilowatts of power with AMC, compared to
52.560 kilowatts of power normally.
WOR also tried the Adaptive Carrier
Control algorithm, but the analog audio quality was affected, the digital
signal was “destroyed” and the power reduction was only about 16 percent,
according to Ray. “It sounded horrendous,” though he said this doesn’t mean it
wouldn’t work for an AM with a different type of format.
Indeed, Mendenhall said ACC gives a
user the greatest power savings with formats whose levels are not running at
peak all the time, such as a lightly processed music format. In contrast, WOR’s
talk levels are processed heavily.
In ACC mode, if the format pauses are
long enough, the automatic gain control in the receiver will start to turn up
the gain in the radio, which can cause the HD to unlock, and blend back to
analog, according to Mendenhall. Such HD dropouts did happen on WOR with ACC.
In contrast, with AMC turned on “we never saw any HD dropouts,” he said.
left: Tom Ray, corporate director of engineering at Buckley
Broadcasting/WOR(AM) in New York, and Harris personnel Terry Cockerill, systems
engineer; Geoff Mendenhall, vice president, transmission research and
technology; and Brian Szewczyk, district sales manager.
Listening tests at weak signal areas on
several types of receivers with digital, analog and synchronous AM detectors
showed no noticeable loss of audio quality. During drive tests with AMC turned
on and off repeatedly, Ray said WOR actually was louder in fringe areas.
reported that Crawford Broadcasting received a waiver to test MDCL algorithms
on station KCBC(AM), San Francisco. The station, which operates at 50 kW power
daytime and 4.1 kW night, planned to test using a Nautel NX50 transmitter,
according to Crawford Director of Engineering Cris Alexander. That system supports
the AMC algorithm as well as Dynamic
Amplitude Modulation. DAM reduces the carrier amplitude at
lower modulation depths where the full
amplitude is not required to prevent negative peak distortion. The audio level
is not adjusted, so this has the side effect of increasing audio volume at low
modulation depths out of the receiver. There is also a corresponding decrease
in signal-to-noise ratio at low modulation depths.