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Example from textbook looks wrong. - RF Cafe Forums
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prolfe
Post subject: Example from textbook looks wrong. Posted:
Tue Jun 02, 2009 6:17 am
Lieutenant
Joined: Tue Jun 02,
2009 6:06 am
Posts: 3
This example (see attachment if I can work
out how to attach a file) from text book seems wrong. Or am I missing
something?
This page is from the book RF Circuit design by Chris
Bowick. Page 74.
The workings seem valid up until at the end
where they simplify the circuits. (Arrow pointing right)
I can
see how A anb b obviously simplify.
But how does C and D simply
+j101 // -j231 into +j107 ???
Is there some kind of magic formula,
or is the book wrong?
I could not actually work out how to attach.
Please look at the image of the page at www.vmsys.com/problem1.jpg
[img]www.vmsys.com/problem1.jpg
[/img]
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Kirt
Blattenberger
Post subject: Re: Example from textbook looks wrong.Posted:
Tue Jun 02, 2009 9:51 am
Site Admin
Joined: Sun Aug
03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Here's the
image (you forgot the http:// part of the URL):
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- Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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prolfe
Post subject: Re: Example from textbook looks
wrong.Posted: Tue Jun 02, 2009 9:59 am
Lieutenant
Joined:
Tue Jun 02, 2009 6:06 am
Posts: 3
Thanks for putting the picture
up. I got all excited thinking you had solved the problem!
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Kirt Blattenberger
Post subject: Re: Example from
textbook looks wrong.Posted: Tue Jun 02, 2009 10:12 am
Site
Admin
Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location:
Erie, PA
Greetings prolfe:
I'll take a stab at the answer
for you, too. First, I think you have a typo in asking how
"But
how does C and D simply +j101 // -j231 into +j107 ?"
The answer
given by the author is 179, not 107.
That particular example
refers to figure D, since it has +j101 (an inductor) in parallel with
-j231 (a capacitor).
Here's how to transform to 179:
+j101
|| -j231 = [(+j101)*(-j231)]/[+j101 + -j231)]
= 23331/-j130 = j179
The "j" indicates positive imaginary reactance, which is an inductor,
so the author gives the value of 179 (ohms) next to the inductor.
Working the circuit "C" example yields the reciprocal of the "D"
circuit, or -j179, which is a capacitor of reactance 179 ohms.
Does that make sense to you, or did I miss something?
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- Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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Components Forum 3
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prolfe
Post subject:
Re: Example from textbook looks wrong.Posted: Tue Jun 02, 2009 10:27
am
Lieutenant
Joined: Tue Jun 02, 2009 6:06 am
Posts:
3
yes yes.. you are somewhat a gun.
the + * - thinggy.
Year 9 maths is somewhat coming back to me now!
I was thinking
it was something more complicated than that.
I had also asked
a mate who studied such things at UNI less than 10 years ago! He did
not pick this up either.
Thanks for your answer.
Regards,
Paul
and yes... my dislexix typing skills have surfaced again.
Posted 11/12/2012
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