[Amps] High SWR,

[Glen Zook]

Power itself is not reflected.  What is reflected is a portion of the wave form and, as such, that can be measured in the same manner as power.  But, in the true sense of the word power is either dissipated as heat in the feedline or is radiated.

If the power was, in fact, actually reflected then the transmitter would definitely have to dissipate this power.  But, in the real world, what is dissipated in the final amplifier of the transmitter (as heat) is the power that cannot be transformed into r.f. energy.  If the r.f. coming from the final amplifier is not properly transformed into the feedline then additional losses (again as heat) will happen and have to be dissipated in the final amplifier.  The match between the feedline and the load (generally the antenna) is another cause of heat generation (this along with the IR losses in the feedline).

The "reflected power" can be measured.  But, since the reflected power is added to the actual power of the transmitter by the instrumentation (this is read a "forward power") and the reflected power reading has to be subtracted from the forward power to indicate the actual power being put from the transmitter into the feedline, therefore, the reflected power can be considered "phantom".  Yes, it can be measured.  But, there is no real physical effect of "reflected power".  Now an improper "match" between the generating device (in this case the transmitter) can result in additional heat being generated.  But, this is different from "reflected power".

If the generation source is "matched" to the feedline but the feedline is not "matched" to the load then VSWR or "reflected power" is going to occur.  There will be no additional losses at the transmitting end but there will definitely be additional losses in the feedline.

There used to be a "white paper" on the Telewave website which gave a detailed explanation of this.  However, I could not find it this morning when I was looking.

Glen, K9STH

Website:  http://k9sth.com


--- On Thu, 4/23/09, Jim Brown <jim at audiosystemsgroup.com> wrote:

Basically, "reflected power" is not real.
 
The author of this false statement would be far better off learning how transmission lines work by studying the ARRL Handbook and ARRL Antenna Book than the manual for someone's SWR bridge. 
 
The concept of reflection energy on transmission lines is QUITE solid. To deny that is to deny Maxwell's Equations!  By the principle of superposition, the current, voltage, and power at any point on a transmission line are the sum of the forward and reflected current, voltage, and power at that point.