Buck wrote:
Thanks, That's what I was looking for. so I can use the antenna with
1/4 - 3/4 or center loaded.

Note that is 1/4WL which is 1/6 distance (16.67%) from
the ends. It is *NOT* 1/4 of the antenna. Hint: There are
six 1/4WLs in a 3/2WL antenna.

Would the off-center setting create another resonant frequency for the
antenna?

Nothing changes much. The radiation pattern will favor the
long side of the antenna. Since the currents are unbalanced
there may be an abundance of feedline radiation.
--
73, Cecil, W5DXP


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Nothing changes much. The radiation pattern will favor the
long side of the antenna. Since the currents are unbalanced
there may be an abundance of feedline radiation.

Then, would the center feed be the best way to go?


--
73 for now
Buck
N4PGW

Then, would the center feed be the best way to go?

For sure. I'd rather center feed, and have to use a
matching device, than use OCF, and not have to use
a matching device. The matching device can be as
simple as a series transformer made from 75 ohm, or
whatever coax. The feed of a 3/2 wave dipole is quite
close to that of a full wave loop. Usually higher than 50
ohms, if clear of the ground. The same series transformer
matching scheme will usually work for either one.
Say if you were on 21 mhz, and the SWR was a bit high.
Say 100 ohms feedpoint impedance, "more common with
antennas high off the ground", you could add 7.6 ft of 75
ohm coax, from the end of the normal 52 ohm feedline,
to the feedpoint of the antenna. That would give you a good
match. Might mess you up on 40m a bit though....I'm not sure
the exact effect it would have on the lower "1/2 wave" frequency.
Maybe not a whole lot...I guess you could switch it in and out
with a relay...BTW....Here, I don't have a very good match on
15 using my 40 dipole, but it's probably cuz I have 160/80/40
on one feedline...I just slap the tuner inline if I want to work 15..
I have used a series transformer on a 3/2 dipole on 20m....It
worked...It was one way I could run a EDZ type antenna, but
easily feed with coax. But...I used .75 wave per side, instead
of the .64 wave per side of the normal EDZ. That tunes out
the reactance, and all you need is the transformer. Sometimes,
you don't even need that as many 40/15 dipoles users know..
MK

Buck wrote:
Nothing changes much. The radiation pattern will favor the
long side of the antenna. Since the currents are unbalanced
there may be an abundance of feedline radiation.

Then, would the center feed be the best way to go?

Balanced center-feeding a balanced antenna will tend to
minimize the common-mode currents but some antennas, like
the Carolina Windom depend upon feedline radiation for
their radiation patterns. What are you trying to
accomplish?
--
73, Cecil, W5DXP

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On Fri, 22 Apr 2005 10:17:55 -0500, Cecil Moore
wrote:

Buck wrote:
Nothing changes much. The radiation pattern will favor the
long side of the antenna. Since the currents are unbalanced
there may be an abundance of feedline radiation.

Then, would the center feed be the best way to go?

Balanced center-feeding a balanced antenna will tend to
minimize the common-mode currents but some antennas, like
the Carolina Windom depend upon feedline radiation for
their radiation patterns. What are you trying to
accomplish?

When trimmed to SWR, I get less than 1.5:1 on fifteen meters. My
plans are to build a multiband antenna, parallel elements, where each
band is 3/2 wave dipoles and fed with 50 or 75 ohm coax. I haven't
tried this yet, but I would hope I can have a few gain dipole antennas
in a multi-band format.


--
73 for now
Buck
N4PGW

I presume you realize that a 3/2 wave dipole has multiple lobes, with
nulls between. At many or most angles, a half wavelength dipole has
greater gain.

You can get just two narrow lobes from a 3/2 wave dipole by rotating the
wires 30 degrees to form a horizontal "V" having a 120 degree included
angle. I've used this trick with a 40 meter dipole being used on 15
meters -- it doesn't have much effect on the 40 meter pattern. (You'll
see some TV antennas made this way for the same reason -- the high TV
channels are about 3 times the frequency of the low channels.) But
again, if a station isn't in the right direction, you'll do better with
a half wave dipole than a 3/2 wave one.

A "gain" antenna isn't of much use if the gain is in the wrong
directions. In fact, it's worse than a lower gain one, since the higher
gain it gets in a few directions comes at the expense of lower gain in
the remainder.

Roy Lewallen, W7EL

Buck wrote:

When trimmed to SWR, I get less than 1.5:1 on fifteen meters. My
plans are to build a multiband antenna, parallel elements, where each
band is 3/2 wave dipoles and fed with 50 or 75 ohm coax. I haven't
tried this yet, but I would hope I can have a few gain dipole antennas
in a multi-band format.

Interesting comments Roy
But it does utelize the use of dipoles that are not straight but angled. It
is well known that pointed /angled dipoles does have advantages such as
reducing rotational area, reduction of
reactances that can lead to as much extra gain as 1 Db together with a
broader
banded antenna.
In this particular case he has achieved an extra 3 db by stacking.
Your point regarding direction of main lobs is quite important but lessens
in importance if the antenna is rotatable. Unfortunately I searched the web
page of this new antenna but was unable to find any antenna patterns,
which puts one in a "believe it or not" situation regarding its capability
versus claims.
Art

"Roy Lewallen" wrote in message
...
I presume you realize that a 3/2 wave dipole has multiple lobes, with nulls
between. At many or most angles, a half wavelength dipole has greater gain.

You can get just two narrow lobes from a 3/2 wave dipole by rotating the
wires 30 degrees to form a horizontal "V" having a 120 degree included
angle. I've used this trick with a 40 meter dipole being used on 15
meters -- it doesn't have much effect on the 40 meter pattern. (You'll see
some TV antennas made this way for the same reason -- the high TV channels
are about 3 times the frequency of the low channels.) But again, if a
station isn't in the right direction, you'll do better with a half wave
dipole than a 3/2 wave one.

A "gain" antenna isn't of much use if the gain is in the wrong directions.
In fact, it's worse than a lower gain one, since the higher gain it gets
in a few directions comes at the expense of lower gain in the remainder.

Roy Lewallen, W7EL

Buck wrote:

When trimmed to SWR, I get less than 1.5:1 on fifteen meters. My
plans are to build a multiband antenna, parallel elements, where each
band is 3/2 wave dipoles and fed with 50 or 75 ohm coax. I haven't
tried this yet, but I would hope I can have a few gain dipole antennas
in a multi-band format.

Please disregard the posting below as I misunderstood Roy's posting was in
reference to a different thread.
Sorry about that
Art
" wrote in message
news:unWae.17625$NU4.2343@attbi_s22...
Interesting comments Roy
But it does utelize the use of dipoles that are not straight but angled.
It is well known that pointed /angled dipoles does have advantages such as
reducing rotational area, reduction of
reactances that can lead to as much extra gain as 1 Db together with a
broader
banded antenna.
In this particular case he has achieved an extra 3 db by stacking.
Your point regarding direction of main lobs is quite important but lessens
in importance if the antenna is rotatable. Unfortunately I searched the
web page of this new antenna but was unable to find any antenna patterns,
which puts one in a "believe it or not" situation regarding its capability
versus claims.
Art

"Roy Lewallen" wrote in message
...
I presume you realize that a 3/2 wave dipole has multiple lobes, with
nulls between. At many or most angles, a half wavelength dipole has
greater gain.

You can get just two narrow lobes from a 3/2 wave dipole by rotating the
wires 30 degrees to form a horizontal "V" having a 120 degree included
angle. I've used this trick with a 40 meter dipole being used on 15
meters -- it doesn't have much effect on the 40 meter pattern. (You'll
see some TV antennas made this way for the same reason -- the high TV
channels are about 3 times the frequency of the low channels.) But again,
if a station isn't in the right direction, you'll do better with a half
wave dipole than a 3/2 wave one.

A "gain" antenna isn't of much use if the gain is in the wrong
directions. In fact, it's worse than a lower gain one, since the higher
gain it gets in a few directions comes at the expense of lower gain in
the remainder.

Roy Lewallen, W7EL

Buck wrote:

When trimmed to SWR, I get less than 1.5:1 on fifteen meters. My
plans are to build a multiband antenna, parallel elements, where each
band is 3/2 wave dipoles and fed with 50 or 75 ohm coax. I haven't
tried this yet, but I would hope I can have a few gain dipole antennas
in a multi-band format.

wrote:
. . .
Your point regarding direction of main lobs is quite important but lessens
in importance if the antenna is rotatable. . .

Absolutely. Most of the comments I made aren't relevant if the antenna
can be rotated.

Roy Lewallen, W7EL

On Sun, 24 Apr 2005 15:12:26 -0700, Roy Lewallen
wrote:

I presume you realize that a 3/2 wave dipole has multiple lobes, with
nulls between. At many or most angles, a half wavelength dipole has
greater gain.

Yes, I believe it has four major lobes and a few minor lobes as well.
None are exactly perpendicular to the wire (IIRC).


You can get just two narrow lobes from a 3/2 wave dipole by rotating the
wires 30 degrees to form a horizontal "V" having a 120 degree included
angle. I've used this trick with a 40 meter dipole being used on 15
meters -- it doesn't have much effect on the 40 meter pattern. (You'll
see some TV antennas made this way for the same reason -- the high TV
channels are about 3 times the frequency of the low channels.)

You got me on this one. I haven't looked into the 'V-Beams'. I was
thinking they were 1/2 wave dipoles. TV antennas are also a form or
Log-Periodic aren't they?

But
again, if a station isn't in the right direction, you'll do better with
a half wave dipole than a 3/2 wave one.
A "gain" antenna isn't of much use if the gain is in the wrong
directions. In fact, it's worse than a lower gain one, since the higher
gain it gets in a few directions comes at the expense of lower gain in
the remainder.


Yes, this is a form of compromise antenna. I guess if I were looking
for the perfect (omni) antenna, it would be a loop.

Many hams use G5RVs or tuned dipoles cut for their lowest desired
band. While they all work, they all have their lobes on certain
bands, probably each band with different lobes.

I realize that the antenna will have nulls and lobes. If possible, I
would want to arrange the antenna in such a way as to use the lobes to
my benefit. Primarily, it is an experimental antenna as much for the
fun of building it as for using it.

I also plan to build a multi-band beam, but not right away.

Thanks for the input. I'll check into the 'V' antenna.


Roy Lewallen, W7EL


--
73 for now
Buck
N4PGW