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Measure Tuner Loss in Matching Circuit - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


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 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.


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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



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