Broadcast Electronics FMI-703

November 1, 2004

In early 2003, we had the opportunity to upgrade WQSX-FM in Boston to IBOC. Because this was in the early days of the IBOC rollout, our choices for transmitter components were limited, but the choices were between reputable companies. We knew that whichever company we chose would stand behind its product.

We calculated that the TPO of the IBOC transmitter would be 2,950W. So, with the need for that power level, not only would we need an IBOC signal generator and an IBOC exciter, but we would also need a transmitter capable of that power level.

Our decision was to purchase the IBOC transmitter.

The product consists of three components: the FSI-10 signal generator, which provides baseband IBOC directly to the IBOC exciter, the FXI-60 IBOC exciter and the FMI-703 transmitter. The FMI-703 is basically the BE FM-10S solid-state transmitter but has been adapted to operate up to 3kW in the digital mode. The FSI-10 and the FXI-60 are rack-mountable components and mount nicely in the FMI-703, although the option exists to mount them in an external rack.

Making connections

Installation was quite easy and can be completed in less than a day's time; the remote control interface was simple, using the optional positive or negative control logic. There are many choices of metering including forward and reverse power, inlet and exhaust temperature, PA voltages and currents along with many status indications available if you choose to use them.

Performance at a glance
Suitable for analog, digital or hybrid operation
Hot-pluggable, solid-state RF modules
Redundant power supplies
Direct-to-channel digital frequency synthesis
Frequency agile
1.25kW to 2.8kW digital
3kW to 7kW hybrid IBOC

The FSI-10 provides a low voltage data stream (LVDS) into the exciter where it combines with the analog signal. The FSI-10 features a touch-screen monitor for all of the system controls. I found that if you don't like working with touch screens, it's convenient to have a stylus that you would use on a PDA. It is imperative that you have this component, if no other, on a UPS for two reasons: first, if you don't follow the sequence of powering down properly, you may corrupt the unit's software. Second, the time to boot the FSI-10 is a few minutes, which will all be off-air time. A UPS will get you through those power glitches without any trouble at all. The FSI-10 also has an optional GPS antenna input.

The last feature that I want to mention on the FSI-10 is the modem and network connections on the unit. These connections made it possible for the BE service department to dial in and upgrade software on one occasion saving the time to send it on CD-ROM.

Detail of the transmitter''s control panel.

The FXI-60 combines the LVDS with the AES audio coming in from our STL. It has a 640 x 480 GUI display that is easy to read and provides all the data you could possibly want for troubleshooting.

The FMI-703 transmitter is used to provide our 2,950W of TPO needed for our IBOC operation. The transmitter is a well-designed unit that can be broken down into three parts: the PA module section, the power supply section and the controller. The PA is a hybrid of 16 PA modules, all of whose status can be monitored on the front-panel LCD multimeter. A loss of a PA module simply reduces the TPO of the transmitter without shutting the transmitter down completely. It does this by reconfiguring the combiner internally. The same theory is in the power supply section of the transmitter: four power supply modules provide more than enough power for this system. In fact, we lost one power supply module and still maintained full power operation with the three remaining modules. The controller is well designed and provides many readings on the LCD multimeter and enough status lights on the front panel of the transmitter to make troubleshooting easy.

Broadcast Electronics

On initial turn-on, we found it came up to our power level just fine. The first glitch we noticed, however, was that the power controller was a little unstable and that the power level would drift unreliably. As mentioned before, though, this was an early transmitter and BE was quick to find that we needed to upgrade the firmware in the controller board and that repair was completed quickly. As the factory has made improvements to the transmitter, we have implemented those improvements and the overall reliability and stability of the transmitter has been great.

This system has been operating for about a year and a half now. We were pleased to not only be the first IBOC on-air in the Boston market, but we were also happy to be able to work with Broadcast Electronics, using an ISDN link from our transmitter site, to provide analog and digital audio to its booth at NAB2003 for the IBOC demonstration.

Kennedy is director of engineering, Entercom Boston.

Editor's note: Field Reports are an exclusive Radio magazine 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 Radio magazine to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by Radio magazine.

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