wrote:
Jim's most recent posting is a good example. We were talking about
measuring current along a dipole. I assumed that would mean measuring
the standing-wave current, but Jim introduced the notion of measuring
travelling wave currents. When challenged as to how we might do that,
we got a URL pointing us to a simple standing wave meter - it
certainly can't discriminate Forward and Reverse.

I just happen to have the answer for anyone with EZNEC. The
following EZ files have been modified to run with the free
demo version of EZNEC.

The following inverted-V antenna is a standing-wave antenna.

http://www.w5dxp.com/inv_v.EZ

The segment currents in one half of the inverted-v look
like this:

EZNEC+ ver. 4.0
actual dipole 5/1/2009 5:12:15 PM
--------------- CURRENT DATA ---------------
Frequency = 3.644 MHz
Wire No. 2:
Segment Conn Magnitude (A.) Phase (Deg.)
1 W1E2 1 0.00
2 .97807 -0.33
3 .93414 -0.65
4 .86875 -0.94
5 .78291 -1.21
6 .67796 -1.46
7 .55552 -1.70
8 .41724 -1.94
9 .26438 -2.17
10 Open .09505 -2.40


The following inverted-V antenna is a traveling-wave antenna.

http://www.w5dxp.com/inv_vT.EZ

The segment currents in one half of the terminated inverted-v
look like this:

EZNEC+ ver. 4.0
actual dipole 5/1/2009 5:22:42 PM
--------------- CURRENT DATA ---------------
Frequency = 3.644 MHz
Wire No. 2:
Segment Conn Magnitude (A.) Phase (Deg.)
1 W1E2 1 0.00
2 .99572 -8.77
3 .99064 -18.12
4 .9799 -27.18
5 .96293 -36.30
6 .94055 -45.74
7 .91497 -55.78
8 .8899 -66.70
9 W3E1 .87103 -79.05

Wire No. 3:
Segment Conn Magnitude (A.) Phase (Deg.)
1 W2E2 .86769 -87.01


The two antennas are identical except one is terminated in
its characteristic impedance and one is not. This is the
best way I know of to illustrate the difference between
the currents on a standing-wave antenna and the currents
on a traveling-wave antenna.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com