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"Ian White, G3SEK"wrote:
Richard Fry wrote: "Ian White, G3SEK wrote The meter measures nothing that involves the source, except the level of RF that it supplies. It does not respond in any way whatever to the source impedance. Not that I said it did in my part of the thread, but nevertheless the above statement is not strictly true. In the case where the source Z of the tx PA does not match its load Z (which is typical), power reflected from the load mismatch will at least partly be re-reflected from the PA -- which then contributes to the power sensed by a "wattmeter" in the output path. Sorry, that statement cannot be correct. It would mean that the impedance you measure at the near end of a transmission line (terminated by some arbitrary load at the far end) would depend on the internal impedance of the device that's doing the measuring - and that is not true, either in transmission-line theory or in the real world. It is a function only of the line and the load. etc ____________ How, then, do you explain the "ghost image" that can occur* in analog(ue) TV transmission systems arising from reflections at/near the antenna end of the station's transmission line? *with sufficient round-trip propagation time in the transmission line RF |
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