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
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
In his book, Prof. Guillermo Gonzalez writes:
V(x)=V+(x) + V-(x) and
I(x)=I+(x) - I-(x)
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?
Post subject: Posted: Fri Mar 07, 2008 4:30 pm
Joined: Wed Feb 22, 2006 3:51 pm
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!
subject: Posted: Fri Mar 07, 2008 5:18 pm
Joined: Fri Mar 07, 2008 2:29 pm
correct. The apparent current has to be defined as the incident wave
current minus the reflected wave current to get the power relationships