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There has been a considerable amount of attention lately regarding the transformation of analog communications systems to digital. With the FCC's recent authorization to permit certain FM stations to implement separate antennas for analog and digital signals and with DTV in place, the question often comes up, "What load is appropriate for my application?" This application note attempts to address the design differences, maintenance and environmental considerations that are important when choosing a termination.

The purpose of a load or termination (also known as a "dummy load") is to absorb RF energy and turn it into heat. Many times the load takes the place of an antenna during transmitter testing. Other applications where terminations can be found are:

• Reject Loads
• Hybrid Combiners
• Isolators / Circulators
• Transmitter Tuning
• System Testing & Calibration

An ideal load will provide a precisely matched absorption of unlimited RF energy over an unlimited frequency range while maintaining a perfect match (a VSWR of 1.0:1).

In the real world, the matching quality of the load varies with frequency. Typically the VSWR of a termination rises with increasing frequency, with the usable frequency range depending on the point at which the VSWR becomes intolerable. Power handling capabilities depend on physical size, construction, duty cycle of the applied signal and more. Selection of the optimum load for a given application involves a thorough understanding of load characteristics and design factors.

Click here to download the complete application note in PDF format.

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