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Questions about some equations in Rohde's book - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


mmaassel
Post subject: Questions about some equations in Rohde's book Posted: Thu Oct 30, 2008 10:41 am

Colonel


Joined: Mon Apr 10, 2006 12:43 pm
Posts: 25
Good day.

I have some questions about an equation in Rohde's book - Communications Receivers (2nd Edition). I am hoping someone can help me unlock my brain.

My first question deals with figures 3.2a and 3.2b (Page 96).

Figure 3.2a
Signal generator (Eg) -> source impedance (Zg) -> voltage noise source 1 (En1) -> noise free network -> voltage noise source 2 (En2) -> load impedance (Zl)

Figure 3.2b
Signal generator (Eg) -> source impedance (Zg) -> voltage noise source (En)-> current noise source (In) -> noise free network -> load impedance (Zl)

The noise free network is described by Z-parameters (Z11, Z12, and Z22)

On page 101 the authors state that the output voltage source (En2) can be replaced by an input voltage source that will produce the same output. The source they come up with is -(E11 + Zg)(En2/Z21). They continue by saying that the open circuit voltage ZgEn2)/Z21)] is just that from an input current source (-En2/Z21)

How do they get the source -(E11 + Zg)(En2/Z21)?

My brain is stuck on this problem and to make matters really annoying I have solved this problem in the past.

Thank you for your time and help.
Michael







Posted  11/12/2012
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