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Problem Understanding Twinax - 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

 Post subject: Problem understanding Twinax
Posted: Tue Mar 13, 2012 7:14 am 

Joined: Tue Mar 13, 2012 6:58 am
Posts: 1

I am currently working on an RF problem that seems to be modelable as twinax joined at the ends.

Can anybody point ot me to a place or help me understand if there would be a capacitance between the two cables when they are joined at the end, or does the short at the end cancel the capacitive coupling between the two coaxial cables?

Thanks in advance.

Kirt Blattenberger
 Post subject: Re: Problem understanding Twinax
Posted: Tue Mar 13, 2012 12:57 pm 
Site Admin

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings DanBot:

Here is a paper from Ansoft on modeling twinax cable, but it does not specifically address your inter-conductor capacitance question.


A good source for searching for an answer is to look up MlL-STD-1553B. It uses twinax for the interface, and there is a plethora of articles, app notes, and datasheets available. You might try calling Belden or any manufacturer and ask to speak to an Applications Engineer. Almost certainly you will get an answer.

- Kirt Blattenberger 
RF Cafe Progenitor & Webmaster

 Post subject: Re: Problem understanding Twinax
Posted: Tue Mar 13, 2012 9:38 pm 

Joined: Sat Nov 08, 2008 11:35 pm
Posts: 3
Location: Ramona, CA
The capacitance would only be negated at DC. With RF you would still have dynamic varying charge distribution down the lines which would vary line to line and produce capacitance on the line. So at RF this capacitance cannot be ignored.

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