Just like the clock that is only correct twice a day, even the highly
regarded Bird 43 "wattmeter" isn't always measuring what you think it
is measuring.
Don W4DNR
Quoting Bill Turner <dezrat@xxxxxxxxxxx>:
According to Ron, K4INM, (original post below) my hypothetical
transmitter is putting out 1000 watts but only 900 is actually
radiated into space. The 100 watt difference is lost in the
transmission line. Correct?
OK, lets suppose I have a superconductive transmission line,
cryogenically cooled conductors with a vacuum dielectric, zero loss.
The SWR is still the same, reflected power is the same, but now where
does the lost power go? Would my SWR meter still show 1000 forward and
100 reflected?
73, Bill W6WRT
**********************************************************************************
Here is Ron's original post:
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.
_______________________________________________
Amps mailing list
Amps@xxxxxxxxxxxxxx
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@xxxxxxxxxxxxxx
http://lists.contesting.com/mailman/listinfo/amps
|