RadioBanter - View Single Post

March 16th 06, 08:07 PM posted to rec.radio.amateur.antenna

wrote:
Cecil Moore wrote:
Note that at the frequency where the dipole is 1/2WL and resonant,
it is 180 feet long and 180 degrees long so the number of feet of
wire is also the number of degrees of antenna. Here is my 1/2WL
dipole with current pickup coils installed at points 'x' and 'y' and
FP is the feedpoint,the impedance of which is 60 ohms.

------------------------------FP-------x---------------y-------

Total length is 180 feet. The distance between 'x' and 'y' is 45 feet.
Since feet = degrees in this case, the number of degrees between
'x' and 'y' is known to be 45 degrees from antenna theory. Those
45 degrees are what I am going to attempt to replace with a coil.

So I adjust the feedpoint current to one amp at a reference phase
angle of zero degrees and measure the current at 'x' and the current
at 'y'. The current at 'x' is 0.92 amp at 0 deg. The current at 'y' is
0.38 amp at 0 deg. Already I am not understanding my measurements.

Your measurements are probably wrong.

When did you measure that? After we resolve the error in current, we
can move on.

The measurement looks good to me. The phase is exactly what EZNEC
predicts -- constant along the wire. The ratio in magnitudes we'd expect
depends on the positions along the wire, not just the spacing.

Roy Lewallen, W7EL