"Richard Harrison" wrote in message
...
Steve Nosko wrote:
"Are the patterns in the handbook all equal power division?"

The subscript says:
"The two elements are assumed to be thin and self-resonant, with
equal-amplitude current flowing at the feed-point."

I see in another post there is also talk of equal power vs equal
currents. This nicely skirts the issue of HOW do you get them to be equal.
I should keep my nose out of these complex discussions, but I think this
supports my original comment that in general, it is not "easy".

Also, Good description of the antenna problem, Richard. Good
refresh of memory. I wouldn't have been able to do it justice from memory.


Since I can`t do diagrams, I suggest finding a copy of the book. It`s a
good one. Best regards, Richard Harrison, KB5WZI

If I had a burning desire to get into this subject I would, but I don't.
Thanks,
--
Steve N, K,9;d, c. i My email has no u's.

I would say yes. This certainly makes sense. The techniques mentioned are
used in fixed frequency broadcast. Any power or phase changes would affect
the pattern and any power matching - dividing network most certainly will
have frequency dependence.

"aa6lk" wrote in message
...
Richard Harrison wrote:
....
The preferred way to handle a negative tower is to feed the energy back
to the power divider, where it will be passed back into the feeder
system again. In this way, all of the energy is radiated rather than
some being dissipated in a resistor.

This makes sense, but I wonder if this condition can be made to hold
true
over the bandwidth of the transmitted signal. Would this scheme result
in
a system that had such a high Q that it would quickly degrade the
further away from the carrier frequency you got (i.e. mismatch at the
sideband frequencies)?

regards
L

Yikes! Double Yikes!! the latest on this thread.

Agreement and a non adversarial discussion of the technology. Good example
fellas. Keep up the good work.
--
Steve N, K,9;d, c. i My email has no u's.

"Cecil Moore" wrote in message
...
acepilot wrote:
Cecil, I think you were implying that the dipoles you modeled were
parallel to each other, correct? Our ELF antennas were dipoles that
were perpendicular to each other. In theory, there should be minimal
interaction between them ....

Yep, that's true, and a turnstile is an example. But for a phased beam,
one needs maximum interaction. ...
! =-----

Steve Nosko wrote:
I see in another post there is also talk of equal power vs equal
currents. This nicely skirts the issue of HOW do you get them to be equal.
I should keep my nose out of these complex discussions, but I think this
supports my original comment that in general, it is not "easy".

It's "EZ" if you use W7EL's SIMPFEED.ZIP stuff :-) downloadable from:
http://www.eznec.com I have modified one of his programs to take the
feedpoint impedances predicted by EZNEC as the inputs to Roy's feedline
phasing program. It's actually "EZ". :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Steve Nosko wrote:
Agreement and a non adversarial discussion of the technology. Good example
fellas. Keep up the good work.

When both sides are technically correct, there can be no valid argument. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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I'll take that as a compliment! I never see a reason to get all bent
out of shape and start name calling anyway. Guess I'm a "Live and let
live" pacifist ;)

Scott
N0EDV



Steve Nosko wrote:
Yikes! Double Yikes!! the latest on this thread.

Agreement and a non adversarial discussion of the technology. Good example
fellas. Keep up the good work.

Again I say, thanks for the compliment! I am by no means an expert on
this topic or antennas in general. I just love antennas! Plus, I was
trying to recall, from my (shorter by the day) memory how our ELF
antennas worked. I haven't worked there for just shy of 9 years...and I
can't even remember what I had for dinner last night ;)

I've often thought of giving the crossed dipoles (I guess you call it a
turnstile antenna) a try on 75M since a 2 element yagi or quad there
might be a bit unwieldy :O Now if I could only remember the math
formula to figure the direction of steering by knowing the phase
difference between the feeds of each antenna. I do remember it was
fairly simple and used sine, cosine, or tangent. Maybe I'll have to ask
a buddy still working there if he can dig the info up in the books
there. Actually, he worked for the company who built the site in the
1980's so he might even be able to pull it from memory. I don't think
that information would be classified :)

Scott


Cecil Moore wrote:

Steve Nosko wrote:

Agreement and a non adversarial discussion of the technology. Good
example
fellas. Keep up the good work.


When both sides are technically correct, there can be no valid argument.
:-)

Scott, N0EDV wrote:
"O Now if I could only remember the math formula to figure the direction
of steering---."

All the simple options are bidirectional except the omni which results
from 90-degree phasing between the two dipoles.

You know that used separately, maximum radiation is broadside to the
energized dipole.

Fed in-phase or out-of-phase, the crossed dipoles have lobes at
45-degrees and 225-degrees, or at 135-degrees and 315-degrees. The
figure-8 pattern is the same as from a single dipole but shifted plus or
minus 45-degrees, depending on in-phase or out-of-phase feed of the two
dipoles.

Patterns of the crossed dipoles are similar to the oscilloscope display
of the same signal fed to both sets of defllection plates but with a
variable or selected phase angle between the plates.

Just by selecting one dipole or the other you could have a north-south
or east-west pattern.

By quadrature feed of the two dipoles you get a near circullar pattern
from the crossed dipoles.

From two dipoles and a 90-degree delay for a non-directional pattern,
and with some switching you get 5 radiation patterns. That`s pretty
versatile.

To get the 90-degree phase shift, a T-network with equal reactances in
all branches is often used. For a 90-degree lag, coils X1 and X2 are in
series with the load. Capacitor X3 connects between junction of the
coils and the other side of the line.

For a 90-degree lead, replace the coils with capacitors, and replace the
capacitor with a coil in the T-network.

It`s easy to remember the reactance values.

X1=X2=X3=Zo= sq rt (ZinZL)

The reactances may well be 50-ohms if we have a match to the usual load
impedance.

To adjust the phase lag of the T-network by as much as plus or minus
15-degrees without significantly affecting the magnitude of the
shifter`s output, X1 and X2 are often ganged variable inductors.

An imperfection in the phase shifter may result from uncertainty about
its input and output impedances. Nevertheless, many T-network phase
shifters are in use.

Best regards, Richard Harrison, KB5WZI

acepilot wrote:
I've often thought of giving the crossed dipoles (I guess you call it a
turnstile antenna) a try on 75M since a 2 element yagi or quad there
might be a bit unwieldy :O Now if I could only remember the math
formula to figure the direction of steering by knowing the phase
difference between the feeds of each antenna.

A turnstile has a fixed 90 degree relationship between the two dipoles.
This makes it somewhat of an NVIS antenna good for satellite communications.
On 75m, a low dipole does approximately the same thing. If you are thinking
of changing the phasing away from 90 degrees, it would technically not be
defined as a "turnstile".
--
73, Cecil http://www.qsl.net/w5dxp



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It's possible to get exact self and mutual impedances from EZNEC. I'll
explain the method for two identical elements.

Excite the two elements with equal, in-phase currents. Record the
feedpoint impedance of either element (they should be the same) as Z0
(= R0 + jX0). Then change the phase of one of the currents to 180
degrees, so the elements are fed exactly out of phase. Record the
feedpoint impedances with this excitation as Z180 (= R180 + jX180).

The mutual impedance Zm = (Z0 - Z180) / 2

The self impedance can also be found as Zs = (Z0 + Z180) / 2

For example, use the Cardioid.EZ EZNEC example file. Change the phase of
the second source to zero, click Src Dat, and note the element impedance
Z0 = 56.11 - j14.22. Change the phase of the second source to 180, click
Src Dat again, and note the impedance Z180 = 16.54 + j16.37. The mutual
Z is then (56.11 - 16.54) - j(-14.22 - 16.37) = 19.8 - j15.3. The self Z
is 36.3 + j1.1. These values can be used in SIMPFEED program Lewall1.

As it turns out, you can also calculate the exact self and mutual
impedances from the feedpoint impedances of two elements fed 90 degrees
out of phase. For identical elements fed with equal magnitude 90 degree
phased currents, where Z1 is the feedpoint impedance of the leading
element (that is, element 2 is fed at -90 degrees relative to element 1)
and Z2 is the feedpoint impedance of the lagging element,

Rm = (X2 - X1) / 2
Xm = (R1 - R2) /2

and

Rs = (R1 + R2) / 2
Xs = (X1 + X2) / 2

Caution: Don't think that because the self impedance is the average of
the two feedpoint impedances in the above two special cases, that it's
always true. It isn't.

Going back to the Cardioid model as it comes with EZNEC, note that
Z1 = 21.03 - j18.71 and Z2 = 51.61 + j20.86 when the elements are fed at
90 degrees. So

Rm = (20.86 - -18.71) / 2 = 19.8
Xm = (21.03 - 51.61) / 2 = -15.3
Rs = (21.03 + 51.61) / 2 = 36.3
Xs = (-18.71 + 20.86) / 2 = 1.1

exactly the values calculated before. Note that the values of mutual
impedance are very close to the values from the graph in Chapter 8 of
the ARRL Antenna Book.

The equations for these special cases are derived from the more general
equations which can be found in Chapter 8 of the ARRL Antenna Book, and
numerous other references. In the 20th Edition of the Antenna Book,
they're Eq 20 and 21 on p. 8-19. Equations can easily be derived for two
dissimilar elements from feedpoint impedances with in-phase and
out-of-phase excitation with equal currents. And although it's possible
to derive equations for self and mutual Z from the feedpoint impedances
of more complex arrays, it requires more "measurements" in order to have
enough equations for the increased number of unknowns.

Roy Lewallen, W7EL

Cecil Moore wrote:
acepilot wrote:

Cecil, I think you were implying that the dipoles you modeled were
parallel to each other, correct? Our ELF antennas were dipoles that
were perpendicular to each other. In theory, there should be minimal
interaction between them because of the nulls off of each end of the
antennas, correct? Somebody else mentioned that the antennas, when
driven, feed power into each other. Placing them at 90 degrees to
each other should minimize interaction, would it not?


Yep, that's true, and a turnstile is an example. But for a phased beam,
one needs maximum interaction. The dipoles in my example are 1/4WL
apart, parallel, and in the same horizontal plane.

Incidentally, one of the disadvantages of Roy's SIMPFEED program is
that one needs to know the mutual coupling impedance between the
elements. For a two-element system, with identical elements, there
is a way to use EZNEC to calculate (estimate) the mutual coupling
impedance, Rm +/- jXm.

For two identical (resonant) elements, the feedpoint impedances reported
by EZNEC will be of the form, (Rs +/- Xm) +/- jRm, where Rs is the
resonant resistance of a single element alone (second element
open-circuited).

For instance, in my earlier example of two 33 ft dipoles, 33 ft apart
at a height of 66 ft, fed 90 degrees apart - the feedpoint impedances
a

109+j34 and 29-j34

That makes Rm = 34 ohms and makes Rs (109+29)/2 = 69 ohms, which
makes Xm = -j39 ohms. Those Rm and Xm values can then be plugged
into Roy's SIMPFEED program to obtain the length of the feedlines.

Note that two phased 20m dipoles work just fine as a beam on 17m.
All it takes is different phasing of the feedlines.