Operational Savings for AM Broadcast with AMC
Switzerland — Operating costs are the focus of every broadcaster today.
Optimizing these costs while minimizing impact on public service and AM broadcast
signal quality is, for many broadcasters, essential in order to remain
profitable enough to stay on the air.
Faced with increasing energy prices, broadcasters
are looking for ways to operate their equipment more efficiently. Now there are
significant potential savings arising from the implementation of modulation
schemes for high power AM transmitters — so called Modulation Dependent Carrier
Level algorithms like Dynamic Carrier Control or Amplitude Modulation
Companding. Any of these and similar schemes modify the carrier power depending
on the degree of modulation depth applied. The potential for energy savings is
a result of the particular technology, its configuration and the program
content. In typical cases, the power consumption of an AM transmitter can be
reduced by 20–40% when compared to regular AM modulation.
These technologies have long been used
by international broadcasters operating high-powered AM transmitters. But
rising energy costs and easier implementation of MDCL algorithms (even in older
transmitters) is focusing attention on ways of extending the benefits. Just
recently the U.S. Federal Communications Commission has approved the
implementation of such MDCL AM broadcasting in the U.S. on a per station waiver
basis, as long as an AM station can maintain its audio quality and coverage
Thomson today recommends AMC as the
preferred algorithm. Audible impact is minimal but with considerable energy
The principle behind AMC is the
absolute peak value detection of the audio signal and the respective dynamic
power adjustment. AMC maintains the absolute RF peak voltage almost constant at
any modulation level by steadily reducing the carrier and its AF signal. This
companding function reduces, for example, the peak voltage to half at 100% modulation,
which leads to a quarter of the nominal peak power energy consumption. For
broadcasters using audio pre-processing to increase the average modulation
level, AMC is a highly economical solution, because AMC works best at high
Recently we have been facing an
increasing demand for AMC implementation in older equipment. At first,
customers were skeptical about AMC and its impact on the carrier power because
of possible deterioration of signal strength and quality in fringe areas. There
was also some skepticism about the expected contribution to energy saving.
According to Gerd Höfs, head of the Transmitter
Department at Deutsche Welle (DW), these misgivings are unfounded.
“We were using DCC or DSB at our high
power stations,” said Höfs, “and we were attracted by Thomson’s offer to
upgrade our transmitters with AMC to reduce our energy footprint.”
“The upgrades were done in 2006 and
2007 respectively, and results have been very convincing: average values over a
longer period show that the use of AMC has reduced our energy costs by 23% as
compared to DCC, and by 35% as compared with DSB, with no reduction in signal
quality reported. Savings could be even greater, depending on program content
and degree of audio compression. We are completely satisfied with this solution
and can fully recommend it,” Höfs concluded.
Heer is head
of customer services for Thomson
information, contact Jean-Charles Daninos in France at telephone at +33-1-34-90-30-11
or visit www.thomson-broadcast.com.