At 8/29/2007 06:40 PM, you wrote: > > >If you have two watt meters and an antenna matching device you can put > > one > > >wattmeter between the transmitter and the matching device and tune it for > > >minimum reflected power on the first meter. Then with a second meter > > >between the tuner and the mismatched load you can see the second > > wattmeter > > >that is reading the reflected power. The second wattmeter will have a > > >higher forward power reading than the first due to the added re-reflected > > >power. > > > > This doesn't sound right either, as there should be no reflected power at > > the antenna if it's been matched further down the line. The tuner would > > be > > adjusted so as to create a conjugate impedance of the antenna at the end > > of > > the feeding coax, thus eliminating the mismatch. > > > > My guess is that the higher power reading on the wattmeter is due to the > > weird impedances it's seeing on both its input & output. > > > > Bob NO6B > > > >Hi Bob, > >Please read again what I wrote. I am not sure that you are following how the >meters are in the circuit. Remember that whatever you do at the transmitter >end of a transmission line has no affect on what is going on in the line >itself. The only thing that will change the swr on the line is what you do >at the load. > >73 >Gary K4FMX
OK, after talking to a senior RF engineer at lunch here at work I think I understand what's going on. The part that threw me was having the matching circuit in the middle of the feedline & the fact that any reflected power from the load MUST be totally re-reflected back by the matching circuit, otherwise there would be power reflected back to the TX, which by definition does not occur in this example. Because of the multiple re-reflections between the matching circuit & load resulting in multiple waves back & forth within that coax section, typical single-wave thinking doesn't apply. I guess it's a useful way to illustrate why coax gets lossier if you use a tuner far from the antenna. Bob NO6B
