I provide contract engineering services to a 1kW Christian station in Norfolk, VA. For several years, the station needed to replace its transmitter. Ongoing repairs to the old one became a problem because it was difficult to obtain the necessary parts. After several bouts with this problem, we discovered that the company providing the parts was going out of business. This is when the search began to find a replacement.
At first, I was a reluctant to consider Armstrong because I was not familiar with the company's products, but after an extensive search, Armstrong offered the best in pricing and packaging. The transmitter was shipped within a week and installation was seamless.
The Armstrong X-1000B transmitter is a compact solid-state AM transmitter that can provide up to 1kW of RF power. The dual 600W RF modules provide some extra headroom for up to 1.2kW output. The modules can be removed while the transmitter is operating to keep the station on the air. The unit can be set for three different preset power levels. The modules are capable of up to 150 percent positive modulation.
Performance at a glance
|Up to 1kW output
HD Radio compatible
Three power level settings
Greater than 90 percent RF PA efficiency
Up to 150 percent positive modulation
Each module has a power indicator to show it is operating. The transmitter itself has indicators to show the presence of the bipolar 20V power supplies and a VSWR and interlock fault. A rotary knob selects the power level setting (high, medium, low), or it can be placed in the remote position to change power remotely.
The front-panel multimeter shows PA voltage and current, forward and reflected power, audio level in and the power output of each RF amplifier.
The rear panel includes the 600 ohm active balanced audio input, the ac power connection (190V to 260Vac) and circuit breaker, the RF output on an N connector, the external RF input to inject a digital signal, and the DB-25 remote control connector.
Installation and operation
The removable RF modules can be pulled and inserted while the transmitter is on the air.
Because of its small size (7RU), the transmitter can easily fit in an equipment rack. The same rack could house the station's audio processors and other equipment as well. It weighs 96 pounds, so it should not be mounted too high in the rack or the rack could tip. Likewise, I would not mount it too low to keep it away from the floor, where it could take in excessive dirt and dust.
One feature that caught my eye is that there are no air filters on the intake. The transmitter relies on the surrounding air to be clean. Because of this, it's important to clean the unit as needed to maintain proper cooling and air flow. The transmitter itself is very easy to work on. All parts are easily accessible, and the pull-out RF amps simplify access.
The transmitter has built-in lightning protection on the RF output. To function properly, two ground connections must be made: One for the electrical ground and one for the RF ground. These must be terminated at the grounding stud mounted on the back of the transmitter.
All routine maintenance is outlined in the owner's manual, which I found to be well organized and complete. I have only encountered one problem with the transmitter when the power supply developed a problem after six months of use. When I contacted Armstrong, arrangements were made to send a replacement by overnight delivery.
I also like the 24-hour, free technical support from Armstrong. If a problem arises that I am not certain how to fix, a phone call is all it takes.
Suggs is the owner of TL Communications, Norfolk, VA.
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