In article , Cecil Moore
wrote:
John Smith wrote:
If you can't make a SIMPLE statement (or paper), on a concept, which an
average layman can understand, you probably don't understand the
concept(s) yourself ... end of story.
Here's a simple statement he could have made about reflected
power not being lost:
In a conjugately matched system using lossless transmission line:
Source Power = Forward Power - Reflected Power = Load Power
Hello, and in a general case one has to be careful in dealing with the
concepts of "forward" and "reflected" when talking about power. It can
become an issue when source impedance, tranmission line characteristic
impedance, and load impedance all have different values. The "matched"
value corresponding to no reflections might not be the value for maximum
power transfer from source to load. In this general case incident
(forward) voltage or current from the source becomes a function of
mismatch between the source and the reference impedance (e.g. 50 ohms) and
the mismatch between the load and reference. When the source is matched
this dependency vanishes and the incident power is the same as the
"available" power (Vsource^2/(4 * Real part of source impedance)) from the
source.
The source can be "matched" to the input of the transmission line feeding
the load but not be conjugately matched to the transmission line/load
combination.
Conversely, we can have reflections present at the source-line interface
for conjugate match conditions. Sincerely, and 73s from N4GGO,
John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337