A transmitter is a major capital expense and will usually see a long useful life at the station. Unless necessitated by a crisis or change in facility, most transmitters will easily serve 10 years or more as a main transmitter, and often serve at least another 10 as a backup transmitter. With such a long lifespan, the transmitter purchase decision is one that carries a great deal of responsibility. With the possibility of a digital transmission standard looming, there are some decisions to be made today that will affect the station in years to come.
So where do you begin? The first step is determining the needed power level, which is the easiest part. The next question may be a little trickier: tube or solid-state? Both designs are in wide use and will provide reliable service. Tubes are obviously a mature technology, but at this point so are solid-state designs. Defining its long-term plans is the third step and the hardest to determine, but is just as important as the other concerns.
When choosing a tube or solid-state transmitter, price is always a concern, and can show an obvious difference when comparing the two technologies. At lower power levels, solid-state designs are less expensive when comparing price to power. At higher power levels, tube designs tend to have an economical edge. The exact power level varies by manufacturer, but for FM transmitters, the power point is around 10kW. For some manufacturers this point might be lower. The options for a new, tube-based AM transmitter are few if any.
As the FM power level need increases, the price point becomes a consideration of the premium for the performance of the solid-state design.
The long haul
If the installation will cover the station for a long term, then digital transmission should be part of the plan. While the exact path for a digital transmission future is not yet known, Ibiquity's IBOC is currently the leading consideration. (Leonard Kahn has begun testing his Cam-D system for AM, but there are no details available yet on this system.)
The three current methods of transmitting an IBOC signal — low-level combining, high-level combining and separate antennas — require different power levels. All of them require linear amplification of the IBOC signal. The opinions vary on which method is best to transmit the IBOC signal.
If the need for a transmitter is short-term, such as an emergency or a temporary installation, the IBOC compatibility may not be relevant. Likewise, a lower-power transmitter could be used, or a used transmitter might be practical. It might also work out that the temporary-use transmitter can serve a back-up purpose later.
Redundancy has become increasingly important over the past few years. Regardless of the need, whether it's weather-related, the result of malicious intent or just a natural event, having suitable redundancy in the transmission system is critical. A completely redundant transmitter site is the ideal situation, but this is not always economically practical. If the budget only allows for a few back-up systems, carefully consider the available options.
Most, if not all modern transmitters, have the ability to patch around failed sections to provide some type of useable, albeit power-reduced, signal. If you choose this approach, keep in mind that you may not be able to work on the trouble while the transmitter is on the air. One example would be a tube FM transmitter. While the IPA may be able to feed the antenna, the entire transmitter may need to be energized to operate this way. If operating a system in a fractional mode like this is part of the redundancy plan, be sure that it can be done practically when the need arises.
One advantage to solid-state designs is that they do not rely on a single amplifier in the final transmitter stage. The final output is created by several power modules that are combined to make the desired power. This soft failure capability allows most solid-state transmitters to continue operating while some of the power modules are not working. Most designs allow one module to fail with no change to the output power. Most designs also allow you to remove a module so it can be repaired while the transmitter is on the air.
The exciter is the one element that does not have inherent back-up. Because of this, it is a good idea to keep a spare exciter available.
As solid-state transmitter manufacturers have refined their manufacturing processes, they tend to use common elements within a product line. For example, a manufacturer may have two transmitters of different power ranges available, but they might use the same power modules within. This repetition of elements can be an advantage to a station or station group in that fewer unique parts need to be kept on hand.
As solid-state transmitters have evolved, their physical size has also been reduced. It's possible to have up to 1kW available in just a few rack spaces. Because of this, a small power amplifier can be added to accompany the back-up exciter for a complete transmitter package. In addition, most solid-state amplifier designs are wideband. With a frequency-agile exciter, a back-up transmitter could be kept in a road case and moved to the transmitter site where it is needed, whether it is within the market or in another city within the station group.
Some manufacturers and dealers of broadcast transmitters
|exciters, solid-state FM transmitters from 30W to 5kW, tube FM transmitters from 1kW to 30kW, solid-state AM transmitters from 500W to 1kW, IBOC
|exciters, solid-state FM transmitters from 100W to 6kW, tube FM transmitters from 800W to 35kW
|exciters, solid-state FM transmitters from 100W to 20kW, tube FM transmitters from 5kW to 25kW, AM solid-state transmitters from 1kW to 10kW, IBOC
|solid-state FM transmitters from 300W to 1.2kW
|exciters, solid-state FM transmitters from 30W to 2kW
|Delta RF Technology
|solid-state FM transmitters from 250W to 5kW, FM power amp modules from 300W to 700W
|DRS Broadcast Technology
|exciters, tube FM transmitters from 11kW to 70kW, solid-state FM transmitters at 5kW
|exciters, solid-state FM transmitters from 300W to 10kW, tube FM transmitters from 1kW to 50kW, solid-state AM transmitters from 250W to 50kW
|exciters, solid-state FM transmitters from 2kW to 40kW, tube FM transmitters from 20kW to 35kW, solid-state AM transmitters from 1kW to 50kW, IBOC
|solid-state AM transmitters from 30W to 100W and 1kW to 50kW, Part 15 solid-state AM and FM transmitters
|exciters, solid-state FM transmitters from 40W to 1kW
|exciters, solid-state FM transmitters from 1kW to 40kW, solid-state AM transmitters from 1kW to 300kW, IBOC
|exciters, solid-state FM transmitters from 100W to 2kW
|exciters, solid-state FM transmitters from 20W to 5kW, tube FM transmitters from 850W to 1.1kW
|exciters, solid-state FM transmitters from 20W to 2kW, tube FM transmitters from 1kW to 15kW
|exciters, solid-state FM transmitters from 100W to 9.6kW, tube FM transmitters from 3.5kW to 30kW
|exciters, solid-state FM transmitters from 100W to 1kW
|Superior Broadcast Products
|exciters, solid-state FM transmitters from 100W to 2kW, tube FM transmitters from 3.5kW to 30kW
|used AM and FM transmitters