QRP viability during solar cycle min?

[Ron D'Eau Claire-2]

Kevin N8IQ wrote:

I've been playing around with EZNEC trying to come up with a DX antenna that
will work at my QTH. The vertical dipole seems to have a fantastic pattern
for DX with low takeoff angles. I may be able to hang a vertical wire dipole
in one of my trees and have it nearly invisible. Anyone have experience with
vertical dipoles that they could share?

----------------------

Are you modeling over a "real earth" in EZNEC, Kevin?

The limitation verticals face is that vertically-polarized waves induce
strong ground currents. In most grounds that means substantial loss of lower
angles of radiation.  

For that reason, most verticals show their maximum lobe at somewhere between
20 and 30 degrees above the horizon. Everything lower is absorbed by the
earth. Until the radiator gets so long the patter breaks up (up to about 5.8
wavelength) there is a slight improvement in gain as the radiator is made
longer.  Using a dipole does eliminate the requirement for a ground for a
Marconi type radiator, but it does nothing to reduce the far-field ground
losses from what I read.

The "gain" of such a vertical will be about 0 dBi or the same as an
"isotropic" radiator.

By comparison, a horizontal antenna 7 MHz, will over 6.5 dBi gain at 20
degrees as long as the horizontal wire is about 1/4 wavelength (33 feet at
40 meters) above the ground. That is equal to a 4:1 power increase just by
making the dipole horizontal! Of course, the horizontal requires a lot more
"horizontal" space! That gain comes from just the reverse of the situation
that costs a vertical signal. The waves from the horizontal are reflected
from the ground to form a sort of "two-element" beam.

Ron AC7AC

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[Benny Aumala]

Q: When QRP is great?
A: Every time!

I have K2 but work with 5W or 500mW.
170 countries 5W and 70 with 20...500mW.

The difference is the same to HiPower boys
whatever sunspot number. It just need your
equipment been correct and some additional
operator skill.

For PROSIGN CONFUSION:
I think letters in abbreviations BK and CL
are separate.

--
Benny        OH9NB
 

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[Stuart Rohre]

L. B. Cebik reports favorably on vertical dipoles at Cebik.com.  When
elevated sufficiently; since they are a complete antenna, not requiring a
radial set; they radiate quite well at DX angles.  See www.cebik.com
-Stuart
K5KVH



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[Ron D'Eau Claire-2]

Stuart, K5KVH wrote:
L. B. Cebik reports favorably on vertical dipoles at Cebik.com.  When
elevated sufficiently; since they are a complete antenna, not requiring a
radial set; they radiate quite well at DX angles.

-------------------------------------------------

You are missing the fact that just because an antenna doesn't need a ground
(that is, it is NOT a "Marconi" antenna) that the ground doesn't have a
dramatic effect on the radiation pattern. Vertical antennas still suffer
from far-field ground loss that horizontal antennas do not and do not get
the reflection gain that horizontal antennas enjoy. The difference is
typically 6 dB lower gain for the vertical under the BEST of conditions over
normal earth, providing the horizontal is >1/3 wave high, and up to about
1/2 wave or so.

That's as basic to antenna performance as the fact that a 1/2 wave radiator
is self-resonant.

Now, if you can raise the vertical up a half wavelength or so, it does help,
but it never gets as good as a horizontal. That is, if the lower end of a
40-meter vertical is 60 to 100 feet high and the top is 66 feet higher you
start seeing some low angle radiation that beats a horizontal at 1/4 to 1/2
wavelength high. But few Hams are in a position to mount a 66 foot vertical
with the base 60 to 100 feet up!

Even with such an extreme vertical, it's gain is still 4 or 5 dB below a
horizontal at 1/3 to 1/2 wave high.

You are absolutely right: Cebik has some excellent material on the WEB and
he deals with this very issue at:
http://www.cebik.com/fdim/fdim4.html

Note the difference in the lower angle radiation from a ground-mounted
vertical with various ground losses from a "perfect" ground to poor. That
"perfect" ground is why verticals work so very well at sea or at the sea
shore. Salt water isn't perfect, but it's a whole lot better than dirt, even
wet, marshy dirt. The only issue I take with that data is that it shows a
horizontal as having the same gain. His scale is wrong, both according to
his other pages concerning horizontal antennas and to other references such
as Moxon or modeling software such as EZNEC. All of those source say the
dipole will be roughly 6 to 7 dB better if it's upwards of 1/2 wave above
the earth.

Verticals work. They work very well. It helps tremendously to have a
full-size (i.e. half wave) vertical since there are no losses that often
appear in a Marconi (1/4) wave vertical, although with care a 1/4 wave can
be very efficient as well. The great work done by Gary Servick, W2FMI,
showing that a 6-foot tall top-loaded 40 meter vertical can be very
effective is a good example. His work was published in QST (one article in
the April 1978 issue) and in other ARRL publicatins such as "Vertical
Antenna Classics" published by the ARRL.

No matter what you do, the polarization of a vertical is still vertical, and
they don't get the reflection gain that a horizontal does from the earth. Of
course, as Cebik points out, you can often phase several verticals to
produce a very effective directional antenna in a lot less space than you'd
need for a similar horizontal antenna on the lower bands.

Ron AC7AC


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[Jessie Oberreuter]

On Thu, 12 Jan 2006, Stephen W. Kercel wrote:

> [...] don't be too enchanted by the low angle pattern, it is also a bit
> lossy. If you overlay your EZNEC vertical dipole elevation pattern with
> the EZNEC broadside elevation pattern of a straight dipole at say 5/8
> wavelength elevation, you'll see that although the vertical concentrates
> its energy at low angles, the actual dBi values are not that much better
> than the horizontal.

      Indeed, a low dipole generally has much better low angle output than
a vertical, but is a lousy dx antenna b/c it isn't a selective listener.
This has lead me to consider using a vertical for listening, and a low
dipole for trasmitting.
      I've been lead to believe that polarization has little effect on HF
reception and propagation outside of the ground wave radius, so next Field
Day, I'm hoping to see if we can't use the above arrangement to kill two
birds with one stone when working dx.  By making t/r antenna switch boxes
for all of the rigs, it should be possible for us to reduce cross-station
interference, and have more low angle punch, by having both stations on a
given band tx on dipoles and rx on verticals.




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[Stephen W. Kercel]

Jessie:

I expect that the only place you'll find that two antennas give you a
consistent advantage is when you try to work long haul DX on 80 and
160 (and maybe 40). The vertical gives you the low angle transmission
assuring that the other fellow will hear you, but most of the noise
is low angle, and you might not be able to hear him over the noise.
In that case a separate receive antenna (such as small loops and
travelling wave antennas) that has low efficiency but favors the
desired signal over noise will be an advantage on receive.

You are correct that no particular polarization of your antenna is an
advantage for receiving skywave signals. The actual polarization will
be a random sum of several different elliptically polarized
components. Those will be different for every signal and will evolve
over time for the same signal.

I have two straight 20 m dipoles, one horizontal and about 45 feet
off the ground, and the other vertical with the feedpoint 20 feet off
the ground. Both have served as excellent QRP DX antennas. Neither
consistently outperforms the other on DX; the better performance on
any given contact depends on propagation conditions. I've confirmed
this with both on the air tests and extensive VOACAP computations.
Clearly because of its high angle component, the horizontal is the
more consistent performer in domestic contests like the NA QSO Party.

Those deep nulls that you see in the theoretical radiation patterns
of dipoles reasonably high off the ground seldom actually occur. The
non-uniformity of the ground electrical properties and ground
elevation mean that the idealized conditions set up the wave
cancellations that produce the nulls do not actually occur. A
practical dipole at a realizable elevation over the ground will be
only slightly superior on its broadside compared to the endfire
direction.The theoretical null of my horizontal points right at
Europe, but I still make lots of European QRP contacts with the antenna.

If you really want an antenna that discriminates against signals from
undesired directions, you need you need a design like a Yagi, a
phased array, or a small loop.

If your interest is in reducing cross station interference between
colocated stations, as on a field day site, you should do some EZNEC
studies using the near field. (Cebik has some material on this.) The
near field patterns that cause interference with nearby equipment
look nothing like the far field patterns.

Also if you're looking for punch on field day, you should do some
VOACAP/VOAAREA angle of arrival calculations customized to your field
day QTH. A great many field day contacts are high angle.

73,

Steve
AA4AK


At 06:51 PM 1/16/2006, Jessie Oberreuter wrote:

>On Thu, 12 Jan 2006, Stephen W. Kercel wrote:
>
>>[...] don't be too enchanted by the low angle pattern, it is also a
>>bit lossy. If you overlay your EZNEC vertical dipole elevation
>>pattern with the EZNEC broadside elevation pattern of a straight
>>dipole at say 5/8 wavelength elevation, you'll see that although
>>the vertical concentrates its energy at low angles, the actual dBi
>>values are not that much better than the horizontal.
>
>      Indeed, a low dipole generally has much better low angle
> output than a vertical, but is a lousy dx antenna b/c it isn't a
> selective listener. This has lead me to consider using a vertical
> for listening, and a low dipole for trasmitting.
>      I've been lead to believe that polarization has little effect
> on HF reception and propagation outside of the ground wave radius,
> so next Field Day, I'm hoping to see if we can't use the above
> arrangement to kill two birds with one stone when working dx.  By
> making t/r antenna switch boxes for all of the rigs, it should be
> possible for us to reduce cross-station interference, and have more
> low angle punch, by having both stations on a given band tx on
> dipoles and rx on verticals.
>
>
>
>

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