Sometimes a SWR meter shows a match on its load side but if it couples
tightly to the line, the SWR on its input isn't matched. That is
probably what is making the Pegasus show higher SWR readings than the
coupler in the tuner. In most ham style couplers, the coupling is
greater (and thus the effect on input match) is greater the higher the
frequency. Sometimes if you can pick a line length between the
transmitter and the SWR bridge (standard Bird technique) that is a total
of a half wave long including the line length of the SWR bridge you can
minimize that effect, though that's tough with 9 HF ham bands.
The big question is whether the input impedance of the tuner plus its
swr bridge is within what the Pegasus will supply full power to or if it
causes a power reduction from mismatch. If the Pegasus won't do full
power through the tuner's swr bridge, its time to scrap that swr bridge
and find one that has less of an adverse effect on the swr. E.g. one
with smaller coupling coefficients, that may need some more DC gain to
run the automated tuner's logic. Though the smaller signal the gets to
the detector diodes the poorer they work without a lot of external help.
Maybe the reflected side needs an RF amplifier before the detector to
make up for loose coupling to the transmission line.
Then maybe the swr bridge is just sloppily made and that makes it upset
the SWR on its input.
Your antenna analyzer and the Pegasus agree that the SWR bridge in the
tuner is the culprit. It probably can be fixed.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.
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