Bird DA25 UHF – Digital Air RF Load (470-890 MHz; 25kW)

Bird DA-Series digital air RF loads are forced air-cooled loads that provide a fully self-contained and convenient means of dissipating large amounts of analog or digital RF power. Digital air loads require no plumbing, pumps, or complicated installation and setup procedures. The four-fan design provides excellent cooling efficiency as well as extremely high reliability.

The RF section of a digital air load is a broadband-tuned device composed of tubular ceramic resistors. These are carefully positioned to produce a very uniform and almost reflectionless line termination over the stated frequencies of the load resistor.

When in operation, the air is forced into all four sides of the unit and directed over the RF resistor network. The heat, developed in the resistors from the dissipation of RF energy, is carried off by the flow of air over the resistor’s surface. The hot air is then exhausted through the grille in the back of the unit.

Bird offers several versions of its DA series RF loads, covering many power levels, as well as VHF and UHF frequency ranges.

Each product page contains a drop down menu at the top where the connector type and AC voltage can be selected.

All digital air loads are supplied with a passive, normally closed, snap disk overtemperature thermoswitch. Normally closed, the switch opens above the maximum safe load temperature, turning off the transmitter power. Because the dissipation of heat generated by the RF power depends upon forced air cooling, if airflow over the resistor array should stop or be restricted, the temperature in the RF chamber can rise beyond a safe limit. The heat sensor will sense the change and actuate the interlock switch to turn off the transmitter. The interlock system will not permit the re‐operation of the transmitter until a lower, safe temperature in the RF housing is reached.

The Digital Air series load may be used in conjunction with any of the Bird rigid coaxial line power meters. When fitted with the appropriate line section and wattmeter, the combination is a useful tool for tuning and adjusting a transmitter as well as monitoring RF power directly in watts.

Broadcasters involved in the transmission of high-definition television, digital audio broadcast, or other signals with complex modulation should use Bird Broadcast Power Monitors (BPM) for the measurement of true average power in these systems. BPMs are also required in applications where multiple carriers are present in the transmission system simultaneously, as in the case of post-combiner power measurements. Conventional broadcast power meters will produce erroneous readings in the presence of complex modulation due to the high peak-to-average power ratio of these signals.