On Sat, 20 Aug 2005 08:51:12 +0000 (UTC), "Reg Edwards"
wrote:


"Richard Clark" wrote
What is the radiation pattern in the horizontal plane?

Just like for the two lobes of a dipole, three lobes for a tripole.

Also what is the equivalent load impedance between each of the line
wires.

35 Ohms.

===================================
Richard,
Would you care to divulge how you obtained these two answers?

Hi Reg,

Sure. Why don't you first confirm them?

On the other hand - how could it be otherwise?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 19 Aug 2005 20:21:38 +0000 (UTC), "Reg Edwards"
wrote:

Is the radiation pattern in the horizontal plane perfectly
omni-directional?

No (and begs the question, what IS perfect?).

On Fri, 19 Aug 2005 22:00:33 +0000 (UTC), "Reg Edwards"
wrote:

What is the radiation pattern in the horizontal plane?

Just like for the two lobes of a dipole, three lobes for a tripole.

Also what is the equivalent load impedance between each of the line
wires.

35 Ohms.

Hardly comes to the class of pageantry in:
On Tue, 16 Aug 2005 16:15:10 +0000 (UTC), "Reg Edwards"
wrote:

Is there anybody about who still imagines that an SWR meter, located
... on the other side of the tuner, indicates
SWR on the transmission line between transmitter and the antenna?

Anybody indeed? Name someone else other than yourself, Reg. Jeesh....

Time to throw in the last spade of earth and say Amen.

73's
Richard Clark, KB7QHC

I ran EZNEC on what I think is an equivalent arrangement, and got a gain
max/min ratio of about 4db. Got an impedance of 29 Ohms. With multiple
sources, I have trouble visualizing what that means. That may actually be 87
Ohms line to line.

Tam/WB2TT

On Sat, 20 Aug 2005 20:00:16 -0400, "Tam/WB2TT"
wrote:

I have trouble visualizing what that means.

Hi Tam,

What do you mean by that? You have a source pushing current into an
element against a counterpoise, an active one albeit, but all
counterpoises support current too (hence the symmetry of resistance).
Just another condition of the ENTIRE structure radiating energy (where
some would have energy cancelled rather than the power product into a
remote load).

Yes, the three leaf trifoil is not very pronounced, and only below an
elevation or 45 degrees or so. However, Reg introduced this with the
strong suggestion of perfection. Perhaps his usual indirection. ;-)

A 4-phase antenna shows a similar lobing to a smaller degree, and a
5-phase antenna is for all practical purposes circular.

I had to solve a problem like this a couple of years ago with a design
for the Army to test their Helicopter pilots for mental alertness.
This involved building a uniform field of even illumination over a
visual angle of 180 degrees horizontal and 90 degrees vertical
(roughly the entire field of view). I was tasked to present no more
variation than a couple of percent ripple. It took about 100 light
sources 1 cM from the eyes.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 20 Aug 2005 20:00:16 -0400, "Tam/WB2TT"
wrote:

I have trouble visualizing what that means.

Hi Tam,

What do you mean by that? You have a source pushing current into an
element against a counterpoise, an active one albeit, but all
counterpoises support current too (hence the symmetry of resistance).
Just another condition of the ENTIRE structure radiating energy (where
some would have energy cancelled rather than the power product into a
remote load).

Yes, the three leaf trifoil is not very pronounced, and only below an
elevation or 45 degrees or so. However, Reg introduced this with the
strong suggestion of perfection. Perhaps his usual indirection. ;-)

A 4-phase antenna shows a similar lobing to a smaller degree, and a
5-phase antenna is for all practical purposes circular.

I had to solve a problem like this a couple of years ago with a design
for the Army to test their Helicopter pilots for mental alertness.
This involved building a uniform field of even illumination over a
visual angle of 180 degrees horizontal and 90 degrees vertical
(roughly the entire field of view). I was tasked to present no more
variation than a couple of percent ripple. It took about 100 light
sources 1 cM from the eyes.

73's
Richard Clark, KB7QHC

Hi Richard,

My main problem was interpreting what EZNEC meant when it told me the
impedance was 29 Ohms at resonance. Missed the fact that it displays the Z
for each generator independently. 29 is the impedance to neutral. So, that
makes it 87 Ohms line to line. I did this in free space. There is no NET
current in the neutral.

Tam

On Sun, 21 Aug 2005 12:03:00 -0400, "Tam/WB2TT"
wrote:

My main problem was interpreting what EZNEC meant when it told me the
impedance was 29 Ohms at resonance. Missed the fact that it displays the Z
for each generator independently. 29 is the impedance to neutral. So, that
makes it 87 Ohms line to line. I did this in free space. There is no NET
current in the neutral.

Hi Tam,

I took the more practical (amusing given the absurd complication of a
3-phase RF source) route of putting the antenna ¼ above earth.

73's
Richard Clark, KB7QHC

On Fri, 19 Aug 2005 20:21:38 +0000 (UTC), "Reg Edwards"
wrote:

There is a 3-phase transmitter feeding a 3-phase antenna via a 3-wire
transmission line.

The antenna consists of three 1/4-wave horizontal radiators spaced at
120 degee intervals.

Is the radiation pattern in the horizontal plane perfectly
omni-directional?
----
Reg.

No. Effectively you are feeding two legs with a -120 degree phase
and that will make it directional.

For Omnidirectional operation ALL legs will have to be fed in phase.
If the three sources are laggin in phase then the feed system will
have to correct the phase till all are in phase.

Many years ago, there was a CB (USA 27mhz 11m) that used three
vertical dipoles with phasing to get directionality or omnidirectional
gain.


Allison

nospam:

That cb antenna (with the 3 dipoles arranged so as to go omni/directional)
was called a "scanner", made by antenna specialists I believe (reed
switches in a relay box control the elements.)

I cut one down, along with the phasing harness to the center of the 10
meter band, works great! And you are correct, the three 120 degree spaced
vertical dipoles are fed in phase for omni-pattern.

John

On Sat, 20 Aug 2005 18:22:29 +0000, nospam wrote:

On Fri, 19 Aug 2005 20:21:38 +0000 (UTC), "Reg Edwards"
wrote:

There is a 3-phase transmitter feeding a 3-phase antenna via a 3-wire
transmission line.

The antenna consists of three 1/4-wave horizontal radiators spaced at
120 degee intervals.

Is the radiation pattern in the horizontal plane perfectly
omni-directional?
----
Reg.

No. Effectively you are feeding two legs with a -120 degree phase
and that will make it directional.

For Omnidirectional operation ALL legs will have to be fed in phase.
If the three sources are laggin in phase then the feed system will
have to correct the phase till all are in phase.

Many years ago, there was a CB (USA 27mhz 11m) that used three
vertical dipoles with phasing to get directionality or omnidirectional
gain.


Allison

On Sat, 20 Aug 2005 11:28:52 -0700, John Smith
wrote:

nospam:

That cb antenna (with the 3 dipoles arranged so as to go omni/directional)
was called a "scanner", made by antenna specialists I believe (reed
switches in a relay box control the elements.)

Yep thats it, got stuck for a name.

I cut one down, along with the phasing harness to the center of the 10
meter band, works great! And you are correct, the three 120 degree spaced
vertical dipoles are fed in phase for omni-pattern.

Many years ago I help a ham friend (now SK) set up a foursquare. that
four vertical monopoles with goundplane with phasing feed for gain and
directionality. It was a very good antenna for 20M.

Early in my commercial career I worked part time for an AM BCB station
and would help with antenna tuning for directional pattern. Imagine
three big (300ft) towers in a field with about that much space between
them in a line. The feed and phasing coils were BIG, the usual
pattern was cartioid with the weak null facing the atlantic ocean to
the southeast. Just a bigger version of many phased arrays I'd see
in my commercial career.

Allison
KB1GMX

Reg, G4FGQ wrote:
"There is a 3-phase transmitter feeding a 3-phase antenna via a 3-wire
transmission line.

The antenna consists of three 1/4-wave horizontal radiators spaced at
120 degree intervals.

Is the radiation pattern in the horizontal plane perfectly
omnidirectional?"

The question is easy, I think. The horizontal 1/4-wave elements have
nulls off their tips, so they can`t produce a perfect omnidirectional
pattern.

Not knowing when to quit, I`ll also speculate that at distant points
from the antenna, the total phase from two elements will produce a total
phase difference of 180-degrees which consists of a total of radiated
field degree difference and path distance degree difference. Maybe more
nulls. I wrote "two elements", because I`m thinking of a dipole in a V
configuration with the 3rd element perpendicular to the dipole as being
more or less along for the ride. Perhaps that`s an oversimplification.

Someone likely has a program which will model Reg`s 3-phase antenna. I
don`t, and I have no experience with 3-phase antennas. I`ve done 3-phase
circuit problems and recognize the balanced load, even if the antennas
are unbalanced.

The system is symmetrical, so each of the loads (antenna elements) takes
the same power. The total load power is 3 times the power of a single
element.

The loads are resonant, so (cos theta) is unity. The elements look like
resistors. Element power is element volts times element amps.

The load is equivalent to a Y-connection.. So, the line to line voltage
is the square root of 3 (1.732) times the volts between the line and
neutral.

Reg also wanted to know the impedance of the antenna, I believe, but its
numerical value depends on construction, height of the elements, their
size, and coupling, if any, to their surroundings. 35 ohms might have
been a good guess.

Voltage to current ratio of the elements gives their resistance.

The volts or amps of the balanced 3-phases can be represented by three
equal arrows separated by 120-degrees. Their instantaneous values always
total zero.

The idea of a polyphase antenna is interesting but I don`t see what
justifies its increased complexity, unless it happens to place nulls
exactly where needed for required protection of broadcasters already on
the air or permitted when a new broadcaster is seeking accommodation. In
that case, the elements would most likely be vertical to launch a decent
ground wave.

Best regards, Richard Harrison, KB5WZI

On Mon, 22 Aug 2005 22:57:05 -0500, (Richard
Harrison) wrote:

Reg also wanted to know the impedance of the antenna, I believe, but its
numerical value depends on construction, height of the elements, their
size, and coupling, if any, to their surroundings. 35 ohms might have
been a good guess.

Hi Richard,

A reasonable guess indeed, given that the monopole with two radials is
not too terribly different.

The idea of a polyphase antenna is interesting but I don`t see what
justifies its increased complexity, unless it happens to place nulls

Well, in phact the fases contribute to null philling - but not
completely so.

In that case, the elements would most likely be vertical to launch a decent
ground wave.

Interesting lobes change, with it turned into an upside down Y (like
the star for a Mercedes) the result is to pump the clouds to more
effect. When turned to present a right side up Y, the result is
distinctly more inclined towards the horizon, but still a better
horizontal polarization performer than vertical (which is attended by
many more variables related to ground and height, of course).

73's
Richard Clark, KB7QHC