engineers are building up experience with modulation-dependent carrier level
operation on AM stations.
using the power-saving MDCL approach is Crawford Broadcasting, as RW has
reported previously. The FCC recently started to allow U.S. AM stations to use
such techniques through rule waivers.
The MDCL at work. This screen shot from KLTT’s NX50 transmitter shows the power output at the instant the shot was taken as 30.5 kW with the power output set to 52.65 kW.
Engineering Cris Alexander provides an update in the company’s latest
“We now have two
full months under our belts with the KCBC modulation-dependent carrier level
operation, which we started in late October,” he wrote, referring to a Crawford
station in Manteca, Calif. “For both November and December of 2011, our energy
usage was reduced by 21% over the same period in 2010.”
also has begun MDCL operations on AM stations WXJC and WYDE in Birmingham,
Ala.; and KLTT in Commerce City, Colo. All these AM stations are using Nautel
“WXJC is another
50 kW AM, and [engineer] Stephen Poole performed the required firmware update
on the AM-IBOC HD exciter to enable the MDCL option. We look forward to gauging
the energy savings at that station starting here in a month or so.”
He wrote that
Poole wanted to try MDCL on 5 kW WYDE as well, “not so much for the energy
savings but as a means to simply reduce stresses on the transmitter. As with
WXJC, all it took was a firmware upgrade and enabling the MDCL option. Once we
learned how, enabling the MDCL option on the new KLTT [Nautel] NX50 was a piece
The stations are
using the AMC algorithm, which reduces the carrier with modulation; it returns
to full power during low or zero modulation.
“I have had the
opportunity to evaluate the effects of the MDCL operation on the signal
firsthand and … well… I haven’t detected any,” Alexander continued. “The signal
is strong and robust, maybe even louder than before, and the digital
performance is outstanding (we get a digital lock in about one second on most
Alexander noted a
related implication: “One thing that occurred to me as I was thinking about all
those power savings is that if we operate our aux transmitters at KLTT or KCBC
(where we have full-power auxiliaries), in about 15 minutes we will produce a
peak demand that is the same as it used to be, something that will really hit
us in the wallet.”
For KLTT, he
wrote, this is not a concern. “The ND50 aux is driven by a two-year-old AM-IBOC
exciter. We were able to do a firmware update to the AM-IBOC and enable the
MDCL option. So now both the main and the aux operate with AMC with 3 dB of
carrier reduction. We can, if we need to, operate the KLTT aux at full power
(including digital carriers) without much of a power cost penalty.”
But at KCBC, its
ND50 aux is driven by an older NE-IBOC exciter that can’t be updated for MDCL.
“So for the moment and until further notice, if we have to use the ND50, we
will operate it at 25 kW to hold the peak demand down and avoid the utility
first-person experiences with MDCL. Write to email@example.com.