An Application Guide For 10 kHz To 3 MHz Impedance Matching AmplifiersSource: AR
Due to a compromise in coaxial power handling capability and efficiency of power transfer, most RF coaxial cables have a characteristic impedance of 50 Ω. To avoid impedance discontinuities and the resultant power reflections, most RF sources are specified with an internal resistance of 50 Ω. There is an electrical engineering theorem that states that maximum power is transferred from a source of fixed internal resistance only when the load resistance matches that of the source. Any variance will result in power reflections in the coaxial transmission line leading to standing waves and energy loss. To preclude this undesirable condition, the vast majority of RF applications attempt to keep the load at or near 50 Ω. To accommodate the majority of these applications, most RF amplifiers on the market have a nominal internal impedance of 50 Ω. Regrettably, many low to midfrequency RF applications are characterized by impedances other than 50 Ω. It is not uncommon to encounter loads varying from 10 Ω to well over 200 Ω in this region. This is especially true in general purpose lab applications where a circuit detail such as load impedance is often unpredictable. AR RF/Microwave has addressed this dilemma with the introduction of the A3 series of amplifiers that can incorporate a variable output impedance to better match those applications with load impedance other than 50 Ω.
The A3 series amplifiers (10 kHz to 3 MHz):
- 800A3 - 800 Watts; Features an internal impedance transformer with selectable output impedance values of 12.5, 25, 50, 100, 150, 200, and 400 Ω. Optional external impedance transformers are available for applications requiring an extended range from 8 Ω to 2k Ω.
- 1500A3 - 1500 Watts; Optional external impedance transformers are available for applications requiring an extended range from 8 Ω to 2k Ω.
- 5000A3 - 5000 Watts
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Application Note: An Application Guide For 10 kHz To 3 MHz Impedance Matching Amplifiers