Measure tuner loss in matching circuit - RF Cafe Forums
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Post subject: Measure tuner loss in matching circuit Posted: Thu Aug 04, 2005 7:55 pm
explain to me the most accurate way to measure the tuner insertion loss in a matching network...Thank you
Post subject: Posted: Fri Aug 05, 2005 8:51 am
Are you really looking for the most
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.
This way a VNA measurement will give you the results.
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.
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
It is 50% of the total loss.
Post subject: Posted: Sat Aug 06, 2005
cool...that is what I thought...May take the total divide by 2 then...thanks guys