I had a thought.
I set the HP 3325B to 10V pk-pk, ran it through the scopematch into
the dummy load. Scopematch showed exactly the expected voltage and
indicated 50 ohms, no reactance.
Next I inserted the low pass filter between the scopematch and dummy
load. There was a slight change indicating R very slightly lower
than 50 ohms (amplitude of current just a tiny bit greater than
voltage), voltage lagging current slightly. It wasn't off by much!
This would seem to be closely in line with Andy's earlier
calculation of 48.5 -j2.86... slightly lower R, slightly capacitive.
The LPF appears to be a bit better near 141 kHz but again, at 137
kHz very little impedance transformation according to this test.
I then moved the LPF to the other side of the scopematch (sig gen >
LPF > scopematch > load) and verified that I see very little
(unmeasurable) loss through the filter.
Paul N1BUG
On 12/24/2017 06:16 PM, Andy Talbot wrote:
Yes
Try anything and try to work out what is happening. But first of
all, he needs to know what power being deliverfed into a 50 ohmsload
is seemingly higher than it 'can' be. The Vdd^2/2/Rl cannot be
violated.
If it appears to be so, then Rl or Vdd or the measurement has to be
wrong.
I once had to go though a similar
try-everything-and-believe-nothing-until-tested process to work out
why my 700Watt 137kHz Tx appeared to be more than 100% efficient!
It turned out my Bird 30dB 1kW attenuator only had 29.4dB
attenuation at DC. And for a 1GHz jobbie, 137kHz is DC.
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