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Measure tuner loss in matching circuit - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
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lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
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Test & Measurement
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
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 re-resonate 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.
a VNA measurement will give you the results.
Post subject: Posted: Fri Aug 05, 2005 11:05 am
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.
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?
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?
Post subject: Posted: Fri Aug 05, 2005 5:14 pm
It is 50% of
the total loss.
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