Hi Jerry,

My application is at only one frequency so I intend to centre it on that
frequency and the VSWR I get is the VSWR I get. I would hope to be 25
dB return loss anyways. I do have a HP8714C network analyzer in the lab I
will be using so that is no problem. Due to the centre frequency (lower
400 MHz) I figure I can only realistically have about 4 of the half wave
elements because of height, weight and wind loading. Oh wait was that 3
or 4 or 5 elements. I still haven't solved that fundamental issue yet. I
don't suppose the radiation pattern is too much of a concern at this
point, as long as it is omnidirectional.

Thomas

Hi Thomas

If you can use whatever frequency the antenna works best at, it may be
practical to build one then use the frequency of best performance with
that antenna. But, if you have some predetermined frequency that the
antenna must perform well at, there is a problem building prototypes. It
can get rather time consuming to build prototypes when using copper pipe.
Aparently you are confident that you can evaluate the antenna's input
impedance. I had figured that would be a fairly difficult task.

I'll be very interested in this project. Please keep the group informed
of your progress.

Jerry KD6JDJ (who has designed similar antennas for
commercial use)



Hi Jerry,

It is a predetermined frequency that I am building the antenna for. It is
not determined if it will become a commercial product yet but I am trying to
design it as such. I can see that it might be a little time consuming
working with copper pipe, but once I get the formula right I should be good
to go. I'll start buy calculating the half wave elements based on theory
knowing my dielectric constant will be dry air or Argon.

The design I have sketch is pretty neat and clean (on paper anyways). It has
all the elements stacked directly on top of each other, unlike the
traditional staggered approach you see in other designs. Also the dielectric
chamber of the transmission elements are sealed and can be filled with a
noble gas such as Argon to prevent corrosion and detuning from humidity.

My background is in receiver and transmitter design, so I'm quite familiar
with impedance matching and I understand how a Smith chart works on a
network analyzer.

I'm looking forward to working with copper pipe instead of 0201 capacitors
and a microscope!

Thomas