Bill W6WRTTurner wrote:
There is something I don't completely understand about the effect of
SWR on an amplifier. Perhaps someone here can clear it up?
Let's say my SWR meter indicates 1000 watts forward and 100 watts
reflected.
1. Does this mean the actual radiated power from the antenna is 900
watts?
2. How much power is the amp actually putting out - 1000 watts or just
900?
2. If the answer to #2 is only 900, why does the SWR meter indicate
1000? Is that a false reading caused by the actual 900 added to the
100 reflected? If so, why does reflected and actual power add to
produce a false reading?
After 60 years in ham radio I suppose I should know this stuff, buy I
must have been absent that day. :-)
All comments appreciated.
Do not worry about the confusion, it is all too common among HAMs even
highly seasoned ones, to get this wrong.
You will soon here the opposite of the following here, but they are
wrong.
The amplifier outputs 1,000 Watts.
900 Watts minus "transmission line loss" X 1.0 is radiated.
100 Watts are reflected by a line to "load mismatch" back to the
"generator" the amplifier (the only cause of any SWR) or reflected
power. This power when it reaches the (generator" the amplifier) finds
a source impedance of under one Ohm, so it is reflected back up the
transmission line experiencing a "transmission line loss" X 2.0 where
90% of that power is radiated.
10 Watts are reflected by a line to "load mismatch" back to the
amplifier finding a source impedance of under one Ohm, so it is
reflected back up the transmission line experiencing a "transmission
line loss" X 2.0 where 90% of that power is radiated.
1.0 Watts are reflected by a line to "load mismatch" back to the
amplifier finding a source impedance of under one Ohm, so it is
reflected back up the transmission line experiencing a "transmission
line loss" X 2.0 where 90% of that power is radiated.
0.1 Watts are reflected by a line to "load mismatch" back to the
amplifier finding a source impedance of under one Ohm, so it is
reflected back up the transmission line experiencing a "transmission
line loss" X 2.0 where 90% of that power is radiated.
100% of the generated power is either radiated or turned into heat
from the transmission line (and balun + antenna wire) losses. (mostly
resistive)
None of the forward power stays in the amplifier, although the
reflected power does change the "loading" of the amplifier, changing
it's operating conditions, from what it was with a pure reactive-less
resistive load.
--
Ron KA4INM - Youvan's corollary:
Every action results in unwanted side effects.
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