OK, more questions on series to parallel conversions and Lnets.
Let's try this one on for size:
Assume a resonant RLC circuit. The input impedance is 4600 Ohms. C is
conected to ground at 7.6 pF. L is 1 uH and is in series with Rout. L
and Rout are connected in parallel to C.
This is a standard Lnet type circuit.
Freq: 28 MHz
OK, find Rout.
According to the design tables in "Solid State Radio Engineering" by
Krauss, Bostian and Raab (page 76), we have the following:
Q = wL/Rout = wCRin (1)
Rin = L/(CRout)=Q/(wC) (2)
= Rout(Q^2+1) (3)
wL = (1/wC)*(Q^2/(Q^2+1)) (4)
OK: w=2*pi*28MHz = 175929600
>From (1) above, we get:
Q= w*C*Rin = 175929600*7.6E12*4600 = 6.02
Also from (1) we can say that: Rout = wL/Q = 175929600*1E6/6.02 = 29.24
Ohms
>From (2) we can say that Rout = L/(C*Rin) = 1E6/(7.6E12*4500) = 29.24
Ohms
However, using (3):
Rout =Rin/(Q^2+1) = 4500/((6.02)^2+1) = 4500/37.24 = 120.83
OK I GIVE UP!!!! WHY DO THE EQUATIONS NOT JIVE??????
I can derive equation (3) from the other equations given, but I cannot
figure out why the numbers can show up different. I must be doing
something obviously wrong or the book has an error in its formulas. So
can someone please tell me why? Yes, I'll feel like an idiot, but at
least I'll have my error corrected.
And secondly, no one has yet explained my Lnetwork vs. series >
parallel transformation question.
With all this brain power here, someone has got to know how to answer
both of these. Or is the brain power only existent when theory is
discussed and not real mathematics?
73,
Jon
KE9NA

Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."

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