

Measure Tuner Loss in Matching Circuit  RF Cafe Forums

sos Post subject: Measure tuner loss in matching circuit Posted:
Thu Aug 04, 2005 7:55 pm Can anyone explain to me the most accurate
way to measure the tuner insertion loss in a matching network...Thank
you
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Guest Post subject: Posted: Fri Aug
05, 2005 8:51 am Are you really looking for the most accurate
way?
What are you calling a tuner? A parallel open circuit
or short circuit stub on a PCB?
If this is the case I suggest
you cascade the network with an impedance inverting length of transmission
line in between and reresonate the matching network to 50 ohms.
When you match back to 50 ohms (only one frequency unfortunately),
you get a system which have the insertion loss of the 2 times the
tuner, plus a quater wave line that you can easily remove from the
loss also.
This way a VNA measurement will give you the results.
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sos Post subject: Posted: Fri Aug 05, 2005
11:05 am There is NO accurate way to measure the insertion loss
of the slug tuner after it tuned to optimize for best performance
in a matching network. However, if you can explain a better measurement
method to measure the slug tuner loss after it tuned to a certain
impedance. A suggestion is to put a 50 ohm line in series with the
tuner which measure the total loss of resistive loss + load mismatch
loss. This idea still questionable because the tuner is not 50 ohm.
Then, this measurement is NOT valid. May I repeat the case: I have
to measure the insertion loss of a slug tuner after it been tuned
to optimize for best performance in a matching network.
Thank
you
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Drew T. Post subject: Posted: Fri
Aug 05, 2005 11:17 am If your frequency is within the BW of
an available oscilloscope, you can always probe the voltage at the
input and at the out of the tuner and get a ratio. Insert a Tee
at both ends of the tuner to probe. Of course, there will be some
abiguity due to the Tees, but you can probably then add back in
the measured IL of the Tees. How exact are you looking to be?
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sos Post subject: Posted: Fri Aug 05, 2005
4:01 pm The slug tuner is connected to the output loadline,
so the impedance transformation at that connection is NOT 50 ohm.
Therefore, we cannot measure the exact insertion loss with the VNA,
because the VNA is the 50 ohms system. How accurate? I guessed that
there is NONE, but better estimate measure technique is what I am
trying to understand...What do you think about use another tuner
to tune the conjugate impedance of the first tuner? Now, we got
50 ohm system...The question is How do we determine the real loss
of the first tuner? Any thought?
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Guest
Post subject: Posted: Fri Aug 05, 2005 5:14 pm It is 50%
of the total loss.
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sos Post subject:
Posted: Sat Aug 06, 2005 3:32 am cool...that is what I thought...May
take the total divide by 2 then...thanks guys
Posted 11/12/2012



