I cleaned up the circuit somewhat. The current sense resistor is now 0.1
Ohm, and the signal is sampled through voltage follower opamps. So, there is
no shunt loading of any kind. I also increased the sampling rate.
For the example where the load is 50 - j400, and source is 0, I now get an
SWR of 66.3. Adding a source impedance of +j400 gives an SWR of 69.1. Since
I am doing a transient analysis, and reading amplitudes off the waveform,
this is about as close as I can get to having the two SWR readings be the
same. PF for the second case is now 86.25W and
PR is 81.02, which gives a
net power close to the desired 5.0. The absolute numbers are clearly
meaningless; only their difference has any meaning.
I also tried a less extreme termination, 50 - j100. This gave an SWR of 5.7.
Conjugate matching at the source gave me 5.8. I think it is safe to say that
source impedance does not affect SWR.
I am going to try some other stuff, The simulator is perfectly happy if ,
for instance, I drive both sides of the meter with a 1KW signal. Either at
the same, or two different frequencies.
Tam/WB2TT
"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
Now for Cecil 1. ZL = 50 - j400. VF=1.62, VR=1.56, SWR=53, PF=1.33W,
PR=1.24W.
Now for Cecil 2. ZL=50-j400, BUT ZS= 0 + J400. VF=11.2, VR=10.9,
SWR=73.7,
PF=64W, PR=60.6W. I am at such a high impedance here, that I suspect the
10K
sampling resistors are loading down the circuit somewhat. (I might try
100K
instead).
Note that there is absolutely nothing explicit in the circuit that has
anything to do with transmission lines. All components are perfect;
there
are no stray inductances or stray capacitors.
Chipman alludes to such a "phenomenon of resonance" in Chapter 10,
"Resonant Transmission Line Circuits". For instance, at a conjugate match
point where 100+j100 is seen looking in one direction and 100-j100 is
seen looking in the opposite direction, there seems to be a *localized*
exchange of extra energy between +j100 and -j100 that can adversely affect
the value indicated by an SWR meter placed between those two values.
--
73, Cecil http://www.qsl.net/w5dxp
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