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

This is surprising to me and doesn't make a whole lot of sense. For one
thing, I would have expected the impedance to vary wildly over the range
shown. For another, the low impedance seems, well, really low.

Is the trend of the data as shown to be expected? Well, maybe the reactive
part? The real part seems to make a little sense except at the extremes.

Can I trust this data to be even approximately right? I mean, can I now say
that the antenna in question is maybe nice due to the natural balun but I
might as well forget it as a simple antenna because to the low impedance?

Or, should I say this is utter nonsense, the antenna is probably okay, it's
just my equipment, setup, or lack of knowledge giving erroneous data?

Your opinions are welcome.

John (KD5YI)