"John Smith" wrote in message
...
Okay, then, I will present data measured this day for this antenna:

http://www.sophisticatedsolutions.us...d%20Dipole.jpg

This is shown in "Antennas for All Applications" on page 820, figure 23-17
(a).

I built the antenna wholly from RG58. The center conductor of the right
half is not connected at either end. It is 14.375 inches wide and averages
a little less than .5 inches between the centers of the top and bottom
conductors. Where the coax is shown exiting the antenna, is a female,
flangeless, chassis mount, BNC connector so that I can replace the antenna
with a short.

My test set up is a VHF oscillator, a vector voltmeter, and a Narda dual
directional coupler. I use a 66 inch piece of RG58 from the output of the
directional coupler to go to the antenna. The short circuits I use are the
best I could make from BNC connectors. The 50 Ohm load I used for
comparative measurements is one of those used for network terminators.
Yes, I am aware they are not instrumentation quality, but it's what I
have.

For a given frequency, I replace the antenna with the short and adjust the
amplitude of the oscillator and the controls of the vector voltmeter so
that the reference channel (A) is 10 mV and the phase is 180 degrees. I
record channel B's amplitude. I then remove the short and connect the
antenna. I then read and record channels A, channel B, and the phase. From
these data I calculate the impedance (per HP's AN 77-3, thanks to Wes
Stewart).

The first item measured is the 50 Ohm terminator. I also measured it at
the conclusion of the tests to see if there were any differences and there
were none.

Here are the results computed from the data:

Freq (MHz) Impedance (Ohms)

410 46.4 + 6.0i (50 Ohm terminator)

380 9.7 - 12.5
390 3.5 - 5.7
400 5.1 + 1.3i
410 5.1 + 6.5i
415 4.0 + 10.0i
425 2.5 + 15.7i
........................................
John,
Discounting the absolute values, the numbers seem to make sense, except for
the 9.7. Might it have been 2.7? There seems to be resonance at around 400.
The impedance goes more reactive in both directions from there, and the real
part goes down monotonically, except for the 9.7

I looked at the picture, and it is not 100% obvious to me what gets
connected at the balanced point. Just for kicks, I am going to try that,
somewhere within the range of an MFJ269.

Tam/WB2TT