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John S · October 11th 14, 05:47 PM posted to rec.radio.amateur.antenna

On 10/10/2014 3:08 PM, wrote:
John S wrote:
On 10/10/2014 1:50 PM, wrote:
John S wrote:
The thread about a new philosophy was about 246 posts long including the
drift into mechanisms of photons and quarks.

I wish to start this thread by discussing the merits of dipoles with
respect to length. I really don't want to start another thread of
flames. Please help me do this.

Let's confine the discussion to...

* It is a wire dipole (keep the wire AWG to practical values, please).
* The dipole's length is variable.
* It may or may not have wire resistance (state your value).
* The source is placed at the center of the antenna.
* There is no transmission line.
* There are no matching devices.
* This is a theoretical discussion but may include practical parameters.

EZNEC or NEC, provides answers to these questions, I think. I will do
some modeling and I'd like to compare my results to other results.

It does.

Let's kick them around.

There is nothing to kick around unless you want to argue about whether
the various NEC implementations provide valid results.

What NEC will tell you is that as the .5 wave dipole gets shorter and
shorter, the resistive part of the antenna impedance decreases and the
capacitive part increases and the patern and maximum gain changes very
slightly.

As the ratio of resistive input impedance to the wire resistance get
smaller, the I^2R losses increase.

But don't let that stop you from doing it.

People often learn much better from actual doing then they do from lectures.

BTW, you have to pay some attention to segmentation and as you get smaller
and smaller the segmentation limits just how accurate the simulation is.

Ok, I guess I had hoped to have a good conversation concerning the subject.

Jim has convinced me that it is not a worthwhile effort.

Cheers.

On the contrary, I think it is quite a worthwile effort especially if
you summarize and publish the results for the benefit of all the arm
wavers saying things like "short antennas are poor radiators".

Then you can discuss real data instead of arguing about what some naif
pulled out of his ass.

Apologies for the blank post. I hit the wrong button.

OK, so lets analyze my results:

Conditions are free space, wire is #14 gauge but may have zero ohms
where noted. The antenna is a dipole with the source connected at the
center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna
resonance plays no part in this. # segments = 99 unless otherwise noted.

Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency

0.5 zero 80 0 2.16 100%
0.5 #14 73.6 -.09 2.08 98%

0.25 zero 13.2 0 1.85 100%
0.25 #14 13.7 -.17 1.69 96%

0.125 zero 3 0 1.78 100%
0.125 #14 3.25 -.33 1.45 93%

0.05 zero .464 0 1.76 100%
0.05 #14 .556 -.78 0.98 83%

Rin is the terminal resistance only. Gave is the average gain integrated
over the pattern, Gmax is the highest gain detected.

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

I invite discussion in any case.

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