Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

transmission line measurements

transmission line measurements

transmission line measurements

I'm incorporating a Linx RF module onto a circuit board.  How to get its RF input to a remote antenna is my challange.  A this point I'd like to connect a couple of small gage stranded wires between the board and a bulkhead SMA connector- one wire soldered to the central post of the connector and the other attached to a ring terminal assembled on the body of the connector.  The wires would be about 1 inch long.  The RF frequency is 918 Mhz.  I'd like to test the assembly for standing waves or impedance.  What would be the proper way to do this?

RE: transmission line measurements

To maintain 50 ohm impedance (assuming that's what you're using), if your circuit board has a ground plane then connecting your IC to the coaxial cable in "microstrip", you'd find the proper width of a connecting line by using the Rogers corp website here

example, Microstrip 50 ohm in dielectric 4.5 and circuit board thickness 0.031 is 0.0569 inches at 1 ghz. Changing dielectric constant to 2.94 for the same board thickness and frequency widens the strip from 0.0569 to 0.0774 inches.

Soldering a wire as you noted is probably fine.

If your circuit card doesn't have a ground plane, that can be a slight problem just attaching two wires to an IC at those frequencies.

Testing the assembly for VSWR requires an vector network analyzer (8753 or 8720 from Agilent, etc.) or if you have a coupler with good isolation performance you could use that to see how much energy reflects off the circuit. Too much detail to describe how to do that shortly.


RE: transmission line measurements

There are a couple of other free transmission line calculators available.
1. - TXLINE 2003 from AWR http://www.mwoffice.com
(you'll need to register to enter the download section.)
It does Microstrip, Stripline, Co-planar Waveguide, CPW Ground, Round Coxial, Slotline, Coupled Microstrip and coupled Stripline.

2. - AppCAD from Agilent  http://we.home.agilent.com
Search for AppCAD, scroll to Design and Analysis tools,
download setup302.exe
It does Microstrip, CPW Ground, Stripline, Parallel Line,
Wire over Ground, Coax Round and Square, Trough Line and Slab Line.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close