When Northwestern College Radio acquired WMAD, Sun Prairie, WI, in
January 1997, one of the first priorities was to replace the
transmitter, a 1981-vintage unit from a defunct manufacturer. The
previous owner spent $2,000 a year on tubes alone to maintain this
unit. We selected the Broadcast Electronics AM-1 but did not purchase
the new transmitter right away as we were also investigating the
possibility of a power increase. We decided to delay the transmitter
replacement until we knew exactly what power level would be needed.
Decision Time In the meantime, the old transmitter started showing
its age in the summer of 2000 and began to fail on a regular basis. One
failure required several days to fix while the problem was diagnosed
and parts were ordered. It was realized quickly that the economies of
replacement-part costs, lost air time and even regular maintenance
expenses made a new solid-state transmitter a smart purchase, even if
the station did receive a power-increase authorization in the future.
To help justify the expense of the new transmitter, station management
used operating cost figures obtained from the salesperson at Broadcast
Electronics. Without any additional expensive breakdowns from the old
transmitter, the new transmitter cost would be recovered in just three
years. Based on the old transmitter's performance over the last six
months, the actual time period was going to be less.
The Northwestern College FM station already owns a Broadcast
Electronics FM transmitter, which has provided outstanding service.
Previous satisfaction made the AM-1A an easy decision, especially with
its reasonable cost. (The AM-1 had been replaced by the AM-1A by the
time we were ready to buy.) The basic transmitter has several standard
features, including a modulation monitor and an AM stereo exciter. It
also provides an array of control inputs and status outputs to
interface with a remote-control system.
One unusual feature of the AM-1A is that it is does not include a
rack enclosure. This feature allows the transmitter to be shipped in
sections by package carriers like FedEx or UPS. The main output
amplifier is rather heavy (packed weight was more than 80 pounds), but
when the need is dire, receiving the transmitter by next-day shipping
is helpful. Installed, the transmitter occupies 42" (24RU) of space.
The station bought a standard, 6-foot, 19-inch rack through a local
audio supplier and had it wired with a welder-type outlet to provide
the 220-volt, single-phase power source for the transmitter.
The transmitter is designed to operate into a 50V load with minimal
reactance. Stations that must feed a load that is not 50V can install
an optional output tuning unit for matching the transmitter to
impedances outside the design range.
The transmitter doesn't have much metering; instead it relies on LED
status indicators (which we call idiot lights) on the front panel for
most status and alert indications. There is a meter for reflected power
and a multi-meter that measures two RF power ranges and AC input
voltage. I would prefer additional metering for PA supply voltage and
Ordering and Installation It only took two weeks from the initial
order for the transmitter to arrive at WNWC. To follow good engineering
practice for solid state transmitters, we also installed AC
surge-protection equipment. An assortment of amenities such as wire
ties, and necessities such as ferrite cores, were provided with the
The transmitter arrived before the equipment rack, which gave us
some time to unpack the unit and study the documentation before
beginning the installation. The transmitter manual is thorough and
readable. By the time preparations were complete at the transmitter
site, we were confident that the rest of the installation would be
Once the rack was delivered, the transmitter sections were installed
easily. The final amplifier section can be installed by two people, but
I recommend having three people available. It is a challenge for two
people to handle the 80-pound section and get the rack screws
On The Air The remote-control cabling, feedlines and AC power went
in without a hitch, and we were ready to start the transmitter.
However, once AC was applied, the transmitter didn't work. This
definitely was not what we expected, but it was the only problem
encountered so far. The front panel indicated that lightning was
present, and we didn't have any clue as to why - it was a bright, sunny
day. As it turned out, the bright sunlight from the open door of the
building was activating the lightning sensor's phototransistor and
providing the false reading. The spark gap and phototransistor are
clearly visible through vent holes at the side of the transmitter.
After covering just enough holes to shadow the lightning sensor, we
were once again ready to test the unit.
First, I ran the transmitter into a dummy load at its lowest power
level, and everything looked fine. Next, I plumbed the transmitter
through an antenna switch into the phasor, and began bringing it up
through the power levels. Again, everything looked fine, though there
was slightly more reflected power than I wanted for the permanent
installation. I didn't have access to a common point bridge, so I used
the transmitter's forward and reflected power metering to adjust the
common point for minimum VSWR at the transmitter's antenna terminals.
This plan worked well, and the station ended up with base currents
within two percent of the licensed values at the licensed common point
current. The resulting reflected power was less than eight watts with
1,100 watts forward power.
The transmitter has performed well since its installation in July
2000.We've had no unplanned downtime since it was put into service. It
also sounds great on the air. Without adjusting the station's on-air
processing, the audio sounds crisper and cleaner on typical radios. The
station has never sounded better on a wideband radio than it does
We are very pleased with the transmitter so far, and we have not
needed manufacturer product support yet. Based on my short experience
with the transmitter, I recommend it to anyone requiring a
straightforward, 1kW solid-state AM transmitter that's easy to install
and inexpensive. I think it's a great buy.
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