Good Evening,

I'd like some advice on building the phasing harness
required for the following antenna:

http://members.tripod.com/~AMN92/cp_ant.htm

It certainly would use 75 ohm RG-6, and i
believe it would be 1 full wavelength, fed in the
center, with the two bays on either end (1/2 wave
to each antenna). You would also need 4 turns of
3-4" diameter coils in the RG-6 at the feedpoints,
to serve as baluns, which decouples antenna currents
down the braid.

So in theory, this should be two 100 ohm
impedances in parallel, for a total of 50 ohms,
which can them be fed with garden variety RG-8 or
RG-213.

Any advice or input is greatly appreciated.


Slick

Dr. Slick wrote:
"I`d like some advice on building the phasing harness required for the
following antenna,"

The antenna described has one-wavelength spacing between antenna
elements. As velocity in the coax is only about 2/3 that in free space,
one-wavelength of phase delay in cable won`t stretch between the antenna
bays as shown. Solution is to add another wavelength of phase shift to
the interconnection cable or to simply use a pair of identical cables of
almost any length to parallel the bays at a driving point. Any desired
phase delay can be added to one or the other of the cables to shape the
pattern.

Best regards, Richard Harrison, KB5WZI

Two bays, well above ground, fed in the middle is about as good as can
be done. That is essentially what anonymous said. --- coax to a T and
equal runs from the T to identical elements ---

[Note that using this scheme with identical HF antennas that are not
many WLs above ground, will not optimize performance.]

As pointed out in a recent thread, the ring-and-stub antenna is
sensitive to small changes in dimensions. [very sensitive] If the
antenna is to be designed to be used where it is desired to have the
free-space vertical and horizontal patterns be close to each other (in
the horizontal plane), as in licensed broadcast applications, expect a
lot of tweaking.

On the other hand, if it is not important to "balance" the patterns,
most any balanced feed system will work to produce most of the gain near
the horizontal plane.

Recently, I was faced with the issue of finding an optimum spacing
of such an array from the face of a solid tower with a diameter of about
0.1 wave lengths. No hope, of course, in having the same real world
vertical and horizontal patterns. However, it was possible to find a
spacing that tailored the two patterns to an acceptable degree. The
modeling needed a very large number of segments!

For amateur use, just space the phase center of the most important
part of the antenna the magic 0.3 wave lengths from the tower surface
and point the antenna in the most desired direction. Fortunately,
because the most common amateur use is probably in conjunction with a
repeater, one would be advised to use good old reliable vertical dipoles
as the elements.

In short, in my opinion, you need to have a mighty good reason to
deal with ring-and-stub antennas. For amateur use, better options
exist.

73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
Home:

Jerry Martes wrote:
"Is it clear to you what this array of two CP antennas will be used
for?"

I hope not fo promote terrorism, but I`m not judging the merits of
application nor advising anyone to break the law. I only advised how to
feed the antennas in phase as need be for radiation to be aiding around
the 360-degrees. As for circular polarization, I would refer any reader
to "Antennas" by J.D. Kraus.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Jerry Martes wrote:
"Is it clear to you what this array of two CP antennas will be used
for?"

I hope not fo promote terrorism, but I`m not judging the merits of
application nor advising anyone to break the law. I only advised how to
feed the antennas in phase as need be for radiation to be aiding around
the 360-degrees. As for circular polarization, I would refer any reader
to "Antennas" by J.D. Kraus.

Best regards, Richard Harrison, KB5WZI

Richard I've been amusing myself by trying to develop an antenna that
"receives" RHCP polar orbiting satellites. The coverage I trying to obtain
would suffer from the stacking refered to in this thread.
And, it seems so obvious that feeding the two antennas in phase would
produce maximum gain on the horizon, that I thought there was some special
requirement for this antenna's pattern.
In addition, I have assumed that the impedance mismatch for receiving
antennas can be allowed to be much greater than for transmitting. This
statement is directed to the fact that transmission line loss is increased
by VSWR, and the reciever isnt restricted to being the same impedance of the
transmission line.

Jerry

"Jerry Martes" wrote in message
...

"Richard Harrison" wrote in message
...
Jerry Martes wrote:
"Is it clear to you what this array of two CP antennas will be used
for?"



snipJerry
I am presently working with circular polarised antennas for transmit,
These antennas are omnidirectional but does produce a choice of TOA
What exactly is the pattern that you are looking for?
I do not have any knoweledge of satellite work needs
Regards
Art

snip