Half Wave Vertical vs. Half Wave vertical Dipole??
Rob
vertical or the half wave vertical dipole??
(I understand that the half wave vertical dipole is the easiest to feed with
50 ohm coax but I don't mind building a matching system for a half wave
vertical if it is worth it for DX)
Has anyone had on air experience with both types of antennas??
73's
Rob
dm
I'll take horizontal over vertical every day I CAN GET IT HIGH ENOUGH. My
current, fixed, wire, two element 40 M beam is at 3/8 wave. I don't think
I'd have tried that, but it was easy to do, so I dropped down my 30 M
same style beam, and hung this one in that spot. So far the results are
super...amazing, in fact. My phased verts on 40 weren't as good...I don't
think, and man! Did they collect electric fence racket! Good luck with
either...you probably wont be able to make YOUR choice until you've tried
both. "DM"
William F. Hagen
dipole.
Bothe should have the same radiation pattern, and hence, the same gain.
A vertical dipole is better than a vertical quarterwave because there is
a null pointing straight up, less cloud warming if the antenna height is
correct. As for the endfeed versus feeding in the center as a dipole,
feeding in the center gives a 50-75 0hm match to coax, can incorporate
either a choke or current balun, you need to engineer supports to hold
the ends in place, and have high voltage at the lower end, so keep clear
to prevent arcing.
As for the end feed vertical, essentially a j-pole, you will probably
use the quarterwave match, which can be used as the support for the
lower end, and can be grounded at the end, but makes the antenna length
a quarterwavelength longer (higher). Also a choke balun (several coils
of coax) to minimize common mode current and radiation from the
feedline.
kc6ufe
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dm
something like 1.5 db stronger in field intensity than a quarter wave
"radiator". This is due to a full current "loop" on it versus only a half
a current loop on the shorter one. It is the same old story...Field
intensity is proportional to the current flowing......73 "DM"
Brian Kelly
>Which antenna is a better DX antenna at low elevations - the wave wave
>vertical or the half wave vertical dipole??
>(I understand that the half wave vertical dipole is the easiest to feed with
>50 ohm coax but I don't mind building a matching system for a half wave
>vertical if it is worth it for DX)
>
If you have a good way to support a vertical dipole and a good way to
pull the coax feedline away from the antenna at 90 degrees the dipole
is much simpler to install and feed and will perform the same or
better than and end-fed vertical.
>
>Has anyone had on air experience with both types of antennas??
>
I have. I've put up several of both. I'll take the dipole if I have a
big tree handy. The verticals go up on open real estate where they
usually have to be ground mounted. Beyond that there are no
differences.
>
Right now I have a 20m dipole strung from the top of a tree, the
bottom end is around ten feet off the ground. It works fine as an
antenna, I can work just about any dx I can hear with a barefoot xcvr
and I can hear just about any signal the guys with the beams in this
area are hearing. But I would not call it a competitive antenna on
20m, ya gotta work to get thru the cw pileups. Any tribander at 50 ft
will spank it. The big downside is that the thing is a noise magnet. I
also have a 475 ft horizontal end-fed wire strung thru the trees at
around 40-50 ft. When I tune a weak signal with the agc / s-meter on
and switch back and forth between the two antennas the noise level
with the vertical is a full s-unit higher than I have with the
longwire and the longwire gives me a little less than an s-unit of
gain. That's 10 or so dB or almost two s-units more noise with the
vertical. It would probably be a lot worse than that if I was in
southern climes like Florida where there is a lot of qrn.
>
>73's
>
>Rob
>
Brian Kelly w3rv
Fractenna
>something like 1.5 db stronger in field intensity than a quarter wave
>"radiator".
It IS?
> This is due to a full current "loop" on it versus only a half
>a current loop on the shorter one.
That is incorrect. According to this logic, an 1/8 wave, lossless dipole is 3
dB below a 1/2 wave lossless dipole.
According to this logic, an infinitesimal losslessloop has zero dBi, when in
fact is has 1.8 dBi.
This is very wrong.
Also, over a large GP a 1/2 wave vertical has MORE than a
full "current loop".
> Funny, It is the same old story...Field
>intensity is proportional to the current flowing......73 "DM"
>
No; field strength depends on the current distribution and ohmic loss.
The question, as posed, is: a 1/2 wave VERTICAL over real ground better or
worse than a 1/2 wave DIPOLE just above real ground?
The answer to this is not obvious; if no one else gets back to you, I'll model
the two and tell you in a couple of days when I can free up a few minutes. My
speculation is that the 1/2 wave vertical, with a good radial system, over real
ground, has the higher f.s.
73
Chip n1IR
>
>
>
>
>
nhbi...@rrzn-user.uni-hannover.de
the question is not so easy to answer.
Over ideal ground, a ground mounted (insulated) half wave vertical is 1.7
dB over a ground mounted quarter wave. This is because in the case of the
half wave, the "upper" and "lower" part of the sineshape current
distribution add up in phase in some directions.
Over real ground, the situation is more complicated. If one wants to have
high gain into low elevation angles, one must use a very big radial
system. This is because the resultant field strength adds up from a direct
component and a component reflected from the ground. Over real ground,
this reflection is lossy and there is a phase shift. This is in connection
with the so called "pseudo-Brewster" angle. In optics, you observe, using
vertical polarized light, that, under some angle, there will be no
reflection from a horizontal oriented dielectric surface. This is the so
called Brewster angle, where the light enters completely the dielectric
medium. If the medium is lossy, all the light is absorbed. The same is
approximately true for radio waves, with the possible exception, that the
assumption of plane waves does not hold very close to the antenna.
The consequence of this Brewster effect is, that you have to improve the
conductivity of your ground very far away from the antenna. For example if
you want a high gain at 20 Degrees, you must provide a hígh conductive
surface at a distance of (lambda/4)/tan(20 Degress) approx 0.7 * lambda
away from the antenna, assuming that the current loop is at 1/4 lambda.
This is true for the vertical dipole and the base fed as well. Because of
the high impedance of the end fed half wave, a good ground is not
important to increase the efficiency.
Using the above assumptions, I would expect no measurable difference
between the vertical dipole and the base fed half wave vertical.
Slight differences might occur because of a slightly modified current
distribution for the base fed vertical, which is slightly different from
the center fed dipole.
I remember modelling the case of a half wave vertical and a quarter wave
vertical over a ground system consisting of 120 quarter wave radials on
average ground (using a MININEC based program with all the inaccuracies
of MININEC) and found, that the quarter wave was several dB better than
the half wave for low elevation angles. So if I had the space I would put
up a quarter wave vertical over a relatively small (in terms of diameter)
radial system. If you can put up your vertical about one wavelength over
the ground, you can get strong radiation below the brewster angle. This is
because for waves striking a lossy dielectric surface under angles below
the Brewster angle, the waves are reflected with a phase shift of about
180 Degress. The reflectivity can be very high in this case. For this
reason, the waves striking the ground under low angles behave similar to
horizontal polarized waves, so that the "the higher the better" crieria
holds. In this case a halfwave is better than a quarter wave (with same
height of current loop) and a 5/8 wave is little better than a half wave.
In this situation I would expect, that the center fed half wave is
slightly better than the base fed because of the more symmetric current
distribution, but I think that it is not worth the efforts one hat to make
to lead the feedline perpendicular to the antenne for at least one quarter
wave length.
Anyway I am looking forward to the results of simulations; perhaps one of
the people having access to NEC-4 can do this for us.
Vy 73
Ralf
DL 6 OAP
Richard Harrison
Is a 1/2-wave vertical over real ground better or worse than a 1/2-wave
dipole just above real ground?
The ARRL Antenna Book has patterns for perfect earth. We know that the
horizontal dipole would produce a doughnut of radiation around the
center of the wire were it not for the presence of the ground. The
ground`s proximity tends to cancel ground-level energy because
reflection from the ground is out of phase for the horizontal wire. A
horizontal dipole near the ground is mostly a cloud warmer. Between 1/4
and 1/2 wavelength elevation above ground the 1/2-wave dipole produces
radiation at useful angles for communications of several hundred to
maybe a thousand miles. Your mileage may vary. Lossy ground reduces the
radiation amplitude and distinction in the pattern shapes.
The ground reflection of a ground mounted vertical 1/2-wave antenna is
in phase with the radiator. Excellent low-angle radiation results. But,
the 30-degree elevation radiation is much less than that produced from
the horizontal dipole at 1/2-wave elevation. So, if you want to talk 200
to 700 miles, more or less, the horizontal 1/2-wave may be a better
antenna for you. For DX, the vertical 1/2-wave with a good ground system
would be hard to beat.
Best regards, Richard Harrison, KB5WZI
Gray Frierson Haertig
Another way to look at the problem of getting good low angle radiation
from a vertical antenna, is to realize that radiation at low angles
(below 10 or 15 degrees) is going to tend to excite ground wave
propagation and not spacewave (or skywave) propagation. Over any ground
that you are likely to encounter on this planet (including sea water),
ground wave propagation is pretty lossy at HF. Certainly lossier than
spacewave or skywave propagation.
I believe this is a restatement in different (functional) terms of what
Ralf is getting at in his post which is more descriptive of the physics.
Because of this, I believe that vertical antennas near the earth ar
doomed to mediocre performance at very low radiation angles (at HF).
This is not to say that they make poor antennas. They are capable of
generating very strong skywave signals at angles of 15 to 45 degrees
(depending on length and ground system) and this will grab you lots of
good DX.
However, it is awfully hard to beat a horizontal dipole if is way off
the ground. This is why most of the big gun SWBC stations use
horizontally polarized curtain arrays. Nothing like stacking a bunch of
horizontal dipoles vertically to get you some gain sideways. (c:
Gray
> Vy 73
>
> Ralf
>
> DL 6 OAP
--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
g...@haertig.com
William F. Hagen
halfwave vertical versus a halfwave vertical dipole.
--
Dennis C. O'Connor
How does the young fella on a city lot get a horizontal dipole "way up in the
air" for 160 meters? Or, for that matter, a vertical half wave dipole?
In general, there has been a lot of dancing of angels on the head of a pin in
this thread...
Denny
Richard Harrison
the vertical dipole and the base fed as well."
A wire doesn`t care how it is excited. The same current in the same wire
produces the same pattern.
To solve stealth and mechanical problems, maybe we could aim a pencil
thin beam of ionizing radiation at the zenith. We might couple our h-f
energy to this conducting shaft by surrounfing it with a toroid excited
from our transmitter.
Details yet to be developed.
W6RCecilA
Seems Star Wars' Laser Swords should be ionizing. The latest Star Wars
even has dipoles. :-)
--
73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
pot
the 1/2 wave above ground has superior performance as compared against the
"ground plane". Remember the dipole has a gain of unity (iso) and the gain
of a ground plane is 0.8......
Now a true 1/2 wave end feed vertical has a "High" input imp
therefore it is not as dependent for a "good" ground as the "high voltage
produced overcomes the "high ground restistance......Of course extra
attention MUST be paid on the decoupling of the feedline in non-ground plane
ants.
Cary Vond
Richard Harrison wrote:
> antenna for you. For DX, the vertical 1/2-wave with a good ground system
> would be hard to beat.
Chipn1ir
With 32 radials, the 1/2 wave vertical has about 0.25 dB more gain than a
vertical half wave dipole over real (good) ground, with radials up about a foot
at 14 MHz.
Essentially they are the same.
73,
Chip n1IR
nhbi...@rrzn-user.uni-hannover.de
I modelled the vertical half wave dipole and the end fed half wave. The
Frequency was 14.1 MHz, the antennas were 0.1 m off the ground (lowest
end of course). I assumed an average ground (following the definition of
the eval version of nec4win 5 mS/m and eps_rel 13). The radial system
consisted of 60 radials and the radius of the radial system was changed
between 2.5 and 20 meters. In all the simulations the (pseudo) end fed
vertical was better than the center fed by about 0.3 dB. The same was true
for ideal ground. All simulation were done with the eval version of
NEC4WIN. The ground is therefore not treated in the Sommerfeld
approximation but rather in reflection coefficient approximation which
does not treat the ground in the near field in the right manner since the
assumptions for the reflection coefficient approximation (plane waves) are
not fulfilled in the near field. I think this explains why I found a
difference of about 3 dB between having no radial system and a very small
radial system of 1 meter radius. For that reason I don't present the
numbers, because I think one cannot take the absolute numbers to serious.
Since difference between the end fed and the center fed vertical exists
for perfect ground as well I would say that one can at least believe in
the difference.
Vy 73's
Ralf
Crazy George
--
Crazy George
Mark Keith
In all the simulations the (pseudo) end fed
> vertical was better than the center fed by about 0.3 dB.
Seems about right to me. Not enough to worry about.
> Since difference between the end fed and the center fed vertical exists
> for perfect ground as well I would say that one can at least believe in
> the difference.
I've tried them both ways here. Never could tell enough difference to
measure. All mine were elevated though, not ground mounted. If any
difference at all, I think the end fed version using a gamma loop feed
may have a bit better feedline decoupling than a coax dipole vertical,
unless the center fed version has decoupling sleeves. But maybe my
imagination... MK
--
http://web.wt.net/~nm5k
Reg Edwards
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Crazy George <mun...@attglobal.net> wrote in message
news:38186...@news1.prserv.net...
Rob
fed point??
If so, what type?? A current balun??
Rob
Brian Kelly <ke...@dvol.com> wrote in message
news:381384ff....@news.dvol.com...
W6RCecilA
> With a half wave centre fed vertical dipole should one use a balun at the
> fed point??
Not unless you are using an unbalanced feedline to feed a balanced antenna.
> If so, what type?? A current balun??
At any balanced/unbalanced transistion in an antenna system, it is good
engineering practice to use a balun. For a resonant dipole center-fed with
coax, the balun of choice is a 1:1 current balun/choke.
Roy Lewallen
common way to mean "coaxial". The currents on a twinlead feedline can be
and are unbalanced by the same mechanisms that cause a coax feedline to
have current on the outside, and a balun will help restore the current
balance in either kind of feedline. Currents will be balanced in either
a coax or twinlead line if it's feeding a symmetrical antenna which is
balanced with respect to ground (e.g., a horizontal dipole), is fed with
a balanced tuner, and is physically symmetrically placed with respect to
the antenna. Otherwise, the currents on either type of feedline can be
unbalanced, and a balun can improve the balance. A J-pole or ground
plane antenna fed with coax (an example of an unbalanced antenna fed
with "unbalanced" line) can result in large currents on the outside of
the coax due to mutual coupling if the coax is particular lengths and
extends downward from the antenna. A balun or baluns can be very helpful
in reducing the current on the outside of the coax in this situation.
Unless you can route the feedline at a right angle to the antenna for a
large distance, you're likely to have unbalanced coupling between your
antenna and feedline. This will result in unbalanced currents in a
twinlead feedline, or current on the outside of a coax feedline. In
either case, the line will radiate and become part of the antenna. This
may or may not present a problem, but in general it's not a good thing.
Putting a current balun at the feedpoint, and maybe a second a quarter
wavelength or so from the feedpoint, will reduce this radiation.
If you're operating your vertical dipole at frequencies where the
feedpoint impedance is very large or very small (typical when using a
single dipole on several bands), a balun might not be effective.
There's more about what baluns do in "Baluns: What They Do and How They
Do It" in the _ARRL Antenna Compendium_, Vol. 1.
Roy Lewallen, W7EL
W6RCecilA
>
> I disagree with Cecil, assuming that he's using "unbalanced" in the
> common way to mean "coaxial".
Oops, I missed the part about it being a *vertical* dipole. What I said
was aimed at horizontal resonant dipoles.
Ian White, G3SEK
>Rob wrote:
>> With a half wave centre fed vertical dipole should one use a balun at the
>> fed point??
>
>Not unless you are using an unbalanced feedline to feed a balanced antenna.
>
Any HF vertical dipole will have one end significantly nearer ground
than the other end, so it has to be unbalanced. That means a balun - or
more correctly, a common-mode feedline choke - will be essential to
avoid feedline currents.
>> If so, what type?? A current balun??
>
>At any balanced/unbalanced transistion in an antenna system, it is good
>engineering practice to use a balun. For a resonant dipole center-fed with
>coax, the balun of choice is a 1:1 current balun/choke.
Yep.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
Brian Kelly
>With a half wave centre fed vertical dipole should one use a balun at the
>fed point??
>If so, what type?? A current balun??
>
This particular antenna was put together as a horizontal antenna for
Field Day, I didn't bother with a balun. The elements are #14 THHN
insulated stranded power wire and the thing is fed with 50ft of RG-8X
it's very light and there is no balun to snag when hauling it up into
trees. It went from being a FD antenna to it's present location and
got strung vertically this time. I arbitrarily put it up so that the
element fed by the coax center conductor is the higher - for whatever
that might be worth, considering that it's an unbalanced antenna ffrom
the gitgo when it goes up vertically. The coax comes off at a 90
degree angle for about 40 ft. This detail would have been difficult to
manage if I had a heavy balun out in the tree. The antenna obviously
works fine. I seriously doubt that I'd get thru the piles any faster
if I'd used a balun. Beware the phenomenon called "overengineering" .
.
>
>Rob
Brian Kelly w3rv
Brian Kelly
Mark Keith
>
> With a half wave centre fed vertical dipole should one use a balun at the
> fed point??
> If so, what type?? A current balun??
Not usually on that type antenna. What they usually do is use "sleeves"
to decouple the feedline from the antenna. There is no balun at the feed
point. The sleeves usually will be a quarter wave long, connected to the
shield at the top, and isolated from shield at the bottom. IE: kinda
like the sleeves on an isopole etc. MK
--
http://web.wt.net/~nm5k
Rob
I am confused with the term "sleeves". Can you please try again to explain
what it looks like. Is a sleeve like a common mode filter?
Rob
Mark Keith <nm...@wt.net> wrote in message news:381A2D...@wt.net...
Richard Harrison
I am confused with the term sleeves.
Sleeves are thin cylinders. They are often used with coaxial antennas as
decoupling devices and as the lower half of a dipole so that the coax
may pass through the radiator. In this common type of coaxial antenna an
additional sleeve may be inserted between the sleeve which serves as the
lower radiating element and the coax jacket. This intermediate sleeve
may decrease coupling between the antenna and coax to prevent feedline
radiation.
One balanced dipole which uses solid conductors for both halves of the
dipole (vertical or horizontal) uses a metal tee. The feedline connects
to the antenna wires inside the tee and the feedline exits the third
pipe of the tee.
The long sleeve of the tee over the feedline is used to decouple the
feedline.
A third 1/2-wave vertical dipole uses an inverted L-form feed for a
1/4-wave element emerging from the heel of the L. The lower end of the L
is the lower half of the half-wave dipole and may also be a
short-circuited stub in some models.
Other examples abound that use decoupling sleeves for 1/2-wave
configurations. Some have conical elements and other imaginitive
configurations.
Mark is right. If you don`t believe it, search the books yourself.
Mark Keith
>
> Hi Mark,
>
> I am confused with the term "sleeves". Can you please try again to explain
> what it looks like. Is a sleeve like a common mode filter?
>
> Rob
Pretty much just a pipe that is larger than the mast that runs up
through the middle of it. Usually a quarter wave long.The sleeves can be
used for the lower part of the antenna also. A decoupling sleeve is open
at the bottom, and is closed at the top, except where the support mast
runs thru the middle. The mast is grounded to this sleeve. Kinda like a
bell. You can also make sleeve arays, which are stacked half waves. Some
of these also add a set of decoupling radials at the base. A sleeve does
the same job as a set of radials overall. Except maybe a bit better if
using wide sleeves like the isopole. Not sure about the "narrow
sleeves".Both versions provide a low impedance to common mode currents
that flow on the shield of the coax or mast. A set of 1/4 radials at a
1/4 wave below the feed will do the same job. MK
--
http://web.wt.net/~nm5k