Homepage - RF Cafe
Webmaster: Kirt Blattenberger | KB3UON | Sitemap | ©1996-2014
Menu below is just a small sample of what is here!
Custom Search
More than 10,000 searchable pages indexed.
•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Transmission Line Question - 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.

Post subject: Transmission Line Question Posted: Fri Mar 07, 2008 2:46 pm


Joined: Fri Mar 07, 2008 2:29 pm
Posts: 3
In his book, Prof. Guillermo Gonzalez writes:

V(x)=V+(x) + V-(x) and

I(x)=I+(x) - I-(x)

Why is there a minus sign in the second equation? The equations say the voltage at a point on the transmission line is the sum of the forward wave voltage V+(x) and the reflected wave voltage V-(x). But the current is the difference of the current of the forward wave I+(x) and the current of the reflected wave I-(x). It seems to me the voltage and the current are vector quantities, i.e. they have a phase. So why the minus sign? Why not just sum them?

Mike Rauh


Post subject: Posted: Fri Mar 07, 2008 4:30 pm


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
If I understand it correctly, it's to make the direction of the power flow work out correctly. Power doesn't really have a phase, but power flow definitely has a direction, and I think the signs are set up to give that.

Hope this helps!


Post subject: Posted: Fri Mar 07, 2008 5:18 pm


Joined: Fri Mar 07, 2008 2:29 pm
Posts: 3

You are correct. The apparent current has to be defined as the incident wave current minus the reflected wave current to get the power relationships right.

Thank you.


Posted  11/12/2012
A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel
Your RF Cafe Progenitor & Webmaster
Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an
                                 engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem! (Seize the Day!)

5CCG (5th MOB): My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website