Field Report: Broadcast Electronics Predator

Not long before I came to work for the Tucson radio stations owned by Journal Broadcast Group, the company had purchased KGMG, a Class-C2 rimshot FM station. Because the transmitter was located on top of a mountain northeast of the city without line-of-sight to some of the outlying suburbs, the station had signal problems in parts of the city, some of which housed desirable demographics. After considerable investigation of the problem, our conclusion was that a fill-in translator was the best solution for fixing the "hole" in the station's predicted coverage. Unfortunately, the FCC had imposed a freeze on new commercial FM translators, but with a great deal of effort we were able to purchase an existing local translator and upgrade its license to suit our needs.

Performance at a glance
  • Self-contained high-power digital exciter
  • Frequency adjustable from front panel
  • Short boot-up period
  • Provision for automatic analog audio backup
  • Simple AC power requirements
  • Connections for PC control
  • When it came time to purchase equipment to build the translator, our goal was to buy a digital transmitter to match the upgrades we've done at our other FM sites. Any of the digital FM exciters currently on the market would probably have been suitable, but our application required a transmitter power output of more than 200W, and our preference was for a standalone transmitter instead of an exciter mated with a power amplifier. Broadcast Electronics' Predator with the optional 250W RF output module nicely fit these requirements.

    Put to use

    The Predator ocupies 4RU, measures 16-inches deep and weighs less than 30 pounds. In addition to the front-panel LED status indicators and modulation meters, there is a small LCD display with a membrane-style keypad, used for setting exciter parameters and displaying various readings. The display may be a little difficult for some to read, but I found the operation of the keyboard to be intuitive and effective.

    The Predator's frequency is set from the keypad. This feature can be disabled via an internal jumper, which is probably the preferred setting. There is also a provision for synchronizing the exciter to an external frequency reference for use in synchronous FM applications.

    Our unit has the digital AES/EBU input module option. One regret is that I didn't include the additional analog composite input module, which would allow for automatic switchover to an analog audio source if the AES signal fails. However, there is a provision to allow use of one of the rear-panel SCA inputs as an emergency composite input, enabled by a single internal jumper change. The Predator's AES input accepts sampling rates from 32kHz to 56kHz, which are converted to its internal 32kHz rate. The manual warns that if any form of compressed audio is fed into the AES inputs, overshoots will result. A digital limiter circuit is included in the digital stereo generator to remove these overshoots.

    The Predator has simple power requirements: 100-240 VAC, 50/60Hz, single phase, which makes it easy to power from a typical rack outlet. AC-to-RF efficiency for the 250W transmitter is specified at 40 percent assuming operation at full power. Once AC power is applied, the unit takes less than ten seconds to boot and produce RF.

    Final preparation

    As soon as the Predator arrived at our office, I put it on the bench and connected it to a dummy load. I ran it at full power for several hours on the bench, and then installed it in its permanent location and ran it for a couple of weeks into a dummy load, without any problems. One minor difficulty presented itself during installation; the Predator, being primarily intended as an exciter, does not have an RF output on-off control, but rather the typical exciter RF “mute” connection for use with transmitter control circuits. An external latching relay was necessary for remotely turning the Predator's RF on and off. The remote interface does include provisions for RF power control and voltage, current and status metering. There are also ports for connecting a PC, either directly or via modem.

    Once on the air, I had the airstaff monitor the translator signal to compare it with the main site's signal. The air staff was quick to notice the slight audio delay from the digital exciter.

    The Predator has operated nearly trouble-free since it was put into service in April of last year. The only problem occurred after a power failure at the translator site, when the backup generator came online briefly; during the switchover back to AC mains, the Predator “glitched” and the RF could not be turned on. The cure was to cycle the Predator's AC power. We've since installed a UPS to protect the unit from AC power line disturbances. Apart from weekly meter readings and occasional dusting of the unit's cooling fan filter, I have not had to perform any maintenance on the Predator.

    I've done informal listening tests between the primary and translator signals. The differences, if any, between the two signals are subtle, as one would expect if both transmitters were being fed from the same processor (although the main transmitter has an analog exciter and a conventional composite STL). The Predator has a fuller low end when compared to the analog transmitter's audio.

    We're happy with the Predator's performance in our fill-in translator application. It has admirably fulfilled our requirement for a self-contained digital exciter/translator transmitter, at a reasonable price.

    Sherrill is chief engineer at KMXZ, KZPT, KFFN and KGMG, Tucson, AZ.

    Broadcast Electronics
    P 217-224-9600
    F 217-224-9607

    Editor's note:
    Field Reports are an exclusive BE Radio feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.
    These reports are performed by the industry, for the industry. Manufacturer support is limited to providing loan equipment and to aiding the author if requested.
    It is the responsibility of BE Radio to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by BE Radio
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