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 think the "Antenna Book" authors were familiar with Kraus` Fig. 11-11
on page 290 of the 1950 edition of "Antennas". Kraus` Fig. 11-11 is
similar to the "Antenna Book" Fig 11 on page 8-8 of the 19th edition.
Kraus makes a point of G.H. Brown`s equal power observations.

I am familiar with the negative-resistance tower occasionally found in a
broadcast array. John E. Cunningham says in the "Complete Broadcast
Antenna Handbook":
"In an array of four towers or more, the resistive part of the
driving-point impedance of one or more of the towers often has a
negative value. This means that the tower obtains its energy through the
mutual impedance between it and the other towers of the array. This is a
confusing situation, but if it is carefully thought out, it will cause
no serious problems. We know the following things concerning the
negative tower:

1. The tower must carry a current of the proper magnitude and phase.
2. The direction of this current is 180-degrees out of phase with what
it would be in a tower having a positive base resistance.
3. We need some method of controlling the magnitude and phase of the
tower current.

The simplest, although not the most efficient way of handling the
negative-resistance tower is to terminate it through a matching network
to a resistor, as swhown in Fig.11-15. The energy that the negative
tower actually gets from the other towers is thus dissipated in the
resistor. The magnitude and phase of the current may be controlled by
the parameters of the network. Naturally, this isn`t a very efficient
arranngement, particularly if the negative tower handles a substantial
amount of current.

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.

Figure 11-16 shows an arrangement for recovering power from a
negative-resistance tower.----"

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

Best regards, Richard Harrison, KB5WZI

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

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

"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.

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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