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Ian White, G3SEK wrote:
W5DXP wrote: If reflected energy could not cause over-current/over-voltage problems in the source there would be no need for protection circuitry. I once burned up a pair of ARC-5 1625's because my feedline came unsoldered at the antenna. If there had not been any reflected power, it would not have happened. Transmitters are damaged *only* by excessive heat dissipation, voltage or current, all caused by the wrong value of load impedance. Reflections don't come into it. Reflections are the *CAUSE* of the wrong value of load impedance. The load impedance on a transmitter when reflections are allowed to reach the transmitter is (Vfor+Vref)/(Ifor+Iref). Please note that half the terms in the impedance equation are reflected terms. Please note that without the reflected terms, the transmitter would probably be perfectly happy with the "right" value of impedance at (Vfor/Ifor). Think what would have happened if you had measured the impedance at the TX end of your o/c transmission line (very high or very low, depending on the length) and replaced it with a resistor and inductor/capacitor giving the same value of R +/- jX. There's no transmission line, so no traveling waves of anything, and no reflections - just a transmitter with a very wrong value of load impedance. The 1625s would have burned up just the same. Yes they would, but in that case reflections are not the cause of the impedance. In the first case, reflections are the *CAUSE* of the impedance that burned up the transmitter. Without the reflections, the transmitter would see (Vfor/Ifor) as the "right" impedance. With the reflections, the transmitter sees (Vfor+Vref)/(Ifor+Iref) as the "wrong" impedance. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
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