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.
No. I do not want to argue. If you do not want to participate, please
feel free to not post in this thread. I'm sure that your knowledge will
be gratefully accepted when you post if you can do so in a gentlemanly
manner.
A bit sensitive, are we?
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.
Not concerned about the pattern.
You should at least be concerned about the maximum gain if for no other
reason than to address claims that very short antennas "do not perform".
As the ratio of resistive input impedance to the wire resistance get
smaller, the I^2R losses increase.
Yes, of course. Which changes faster?
I can't say as I have never plotted the data but it would be informative
if you were to do so if you are going to do this.
I would think a plot of I^2R loss versus length in wavelength for at
least two different wire sizes would be instructive, e.g. #8 and #18.
But don't let that stop you from doing it.
I have never let other people's opinions stopped me from exploring and
learning.
People often learn much better from actual doing then they do from lectures.
True. Today, however, it is nice to be able to explore so many
configurations without spending a lifetime of climbing trees or erecting
support poles or installing towers, or....
Yes, simulations prevent a lot of wasted effort.
I once got a hare brained idea for an antenna and modeled it first.
It turned out to be easy to construct with good gain, but an input impedance
in the order of an Ohm and impractical to feed.
Oh well...
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.
I know how that is done. Is this information for me or the other readers?
For whoever is not aware that such limitations exist.
--
Jim Pennino