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Cecil Moore wrote:
Reg Edwards wrote: I wonder why most commercial finals are protected from a high SWR by foldback circuitry to avoid damage to the finals? They don't. There isn't an SWR meter on the station. Reg, I'm talking about commercially manufactured ham radio finals. Virtually every single one of them has protection circuitry and virtually every one of them has a built-in SWR metering system. I'll stand to be corrected because my RF design activity, C-Band and S-Band satellite circuits, ended in the mid 80s. Back then, an antenna load outside of the design range causes higher emitter currents in the bi-polar solid state devices. These higher currents are the damage producers. So, circuits were added to control the maximum emitter current. Today's semiconductor technology is different but I still suspect that localized voltage or current stresses are a function of the load. We used to design for a plasma enhanced environment with an intrinsic Zo range between 120 to 377 ohms, or, slightly more than 3:1 VSWR at the antenna. BTW, the circuits continued to operate at almost 10:1 VSWR!! |
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