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July 6th 15, 12:03 AM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
Roger Hayter wrote:
wrote: Brian Reay wrote: On 05/07/2015 21:17, wrote: Roger Hayter wrote: snip The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. They are designed to drive into a 50 ohm load, that doesn't mean they have a 50 ohm source impedance. Otherwise efficiency would be rather 'disappointing'. Nope. If they didn't have a 50 Ohm source impedance, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. The SWR looking into the cable from the transmitter is unaffected by the source impedance. Indeed, it is exactly the same if the transmitter is not connected (though you have to connect some kind of generator in order to measure it, it matters little what kind it is.) If the input end is not connected, SWR is meaningless. SWR bridges are calibrated to the source impedance, not the load. -- Jim Pennino |
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