Thread: Observations
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Old September 29th 08, 05:47 PM posted to rec.radio.amateur.antenna
Cecil Moore[_2_] Cecil Moore[_2_] is offline
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First recorded activity by RadioBanter: Mar 2007
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Default Observations

Jeff Liebermann wrote:
That's normal. You're not measuring forward power. You're measuring
RF voltage near the radio antenna connector. Once the load (coax +
antenna) moves away from a 50 ohm resistive load, all bets are off as
to what the voltage means. The same for a VSWR meter or watt meter
installed between the radio and the coax cable to the antenna. Once
the load gets away from 50 ohms, the voltage readings are not an
indication of power.


It's not an indication of *NET* power but it is certainly an
indication of forward power (or reverse power). If it weren't
anyone could sue Bird for false advertising.

That begs the question "What happens to a transmitter if one
intentionally runs it with a high VSWR?" I don't know the full
answer. Conventional wisdom is that the xmitter finals overheat. I've
never seen much of that except with a tube power amplifier.


A high VSWR can cause over-voltage or over-current conditions
depending upon phase. Over-current conditions can indeed cause
the finals to overheat. Over-voltage conditions can cause punch-
through of the finals. The key to understanding the effect of
SWR on the finals is in understanding constructive and destructive
interference.
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein