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Voltage Gain Determination - RF Cafe Forums
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Post subject: Voltage Gain Determination
Posted: Wed Jan 20, 2010 1:35 pm
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Joined: Tue Dec 15, 2009
10:22 am
Posts: 9 |
Hello I'm trying to obtain the voltage transfer
function employing an E5062A VNA. From pages
24, 23 in:
http://cp.literature.agilent.com/litweb ... 2-1087.pdf
I see that it can be obtained in terms of the
S parameters and the load reflection coefficient.
My question is: is it correct to assume
that the source and load impedances are equal to
the reference impedance (Zl=Zs=Zo=50 Ohm)? In
this case, the expression in page 24 of the document
would reduce to Av=S21/(1+S11). Is it correct?
Thank you very much.
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fred47 |
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Post subject: Re: Voltage Gain Determination
Posted: Fri Jan 22, 2010 11:49 pm
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Joined: Wed Feb 22, 2006
3:51 pm
Posts: 113 |
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When you measure a device with a VNA, the source
impedance from the VNA is 50 Ohms (normally, unless
you're in the TV industry, where they use 75 Ohms
a lot). Likewise, the load impedance seen by the
device you're testing is 50 Ohms, again due to the
VNA.
Remember to use complex arithmetic when
you use the equations!
Good luck!
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Measures |
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Post subject: Re: Voltage Gain Determination
Posted: Mon Jan 25, 2010 6:24 am
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Joined: Tue Dec 15, 2009
10:22 am
Posts: 9 |
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So... can I assume that the reflection coefficients
of the source and the load are zero and, then the
referred expression is simplified as I said?
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fred47 |
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Post subject: Re: Voltage Gain Determination
Posted: Mon Jan 25, 2010 1:27 pm
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Joined: Wed Feb 22, 2006
3:51 pm
Posts: 113 |
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Basically, yes.
But it's more precise to
say that the source and load impedances (50 Ohms
+ j0 Ohms) determine the reference impedance.
If you connect a short piece of low-enough
loss transmission line of characteristic impedance
50 Ohms between the two ports of the VNA, then calibrate
out the length of the line, you'll get zero for
S11 and S22, and one for S21 and S12 - which I think
is the answer you're looking for, stated precisely.
Good luck!
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Posted 11/12/2012
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