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what homebrew HF antenna produces the most groundwave?



 
 
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  #1  
Old September 30th 07, 02:39 AM posted to rec.radio.amateur.antenna
Anonymous[_2_]
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Posts: 8
Default what homebrew HF antenna produces the most groundwave?

Of all the HF antennas one might reasonably make out of wire or
aluminum tubing, which produces the strongest groundwave?
Ground-mounted quarter-wave vertical? Horizontal dipole at a height of
1/4 wavelength? Or what? I'm sure someone must have experimented, or
done computer modelling, to seek an answer to this question but I am
not finding any information.

--
-30-
  #2  
Old September 30th 07, 03:29 AM posted to rec.radio.amateur.antenna
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Posts: 658
Default what homebrew HF antenna produces the most groundwave?

On Sep 29, 8:39 pm, Anonymous wrote:
Of all the HF antennas one might reasonably make out of wire or
aluminum tubing, which produces the strongest groundwave?
Ground-mounted quarter-wave vertical? Horizontal dipole at a height of
1/4 wavelength? Or what? I'm sure someone must have experimented, or
done computer modelling, to seek an answer to this question but I am
not finding any information.

--
-30-


If all things are set up properly, normally the 5/8 will give the
strongest
ground wave for a single element. You have very little if any true
ground
wave from a horizontal antenna. You do have a space wave, but it's
not
quite the same.
MK

  #3  
Old September 30th 07, 06:43 PM posted to rec.radio.amateur.antenna
Wimpie
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Posts: 106
Default what homebrew HF antenna produces the most groundwave?

On 30 sep, 03:39, Anonymous wrote:
Of all the HF antennas one might reasonably make out of wire or
aluminum tubing, which produces the strongest groundwave?
Ground-mounted quarter-wave vertical? Horizontal dipole at a height of
1/4 wavelength? Or what? I'm sure someone must have experimented, or
done computer modelling, to seek an answer to this question but I am
not finding any information.

--
-30-


Hello "Anonymus".

I assume that you want to maximize field strength close to ground.
At the low HF (and of course medium wave), the surface wave
contributes lots to the signal strength. These ones you can only
excite with a vertical polarized antenna. Also elevated vertical
antennas induce surface waves, so a ground connection is not mandatory
(but many times required practically because of antenna size).

As mentioned by other poster, 5/8lambda vertical fed over a good
ground network gives highest gain in horizontal plane (with a minor
side lobe).

At high frequency (and low ground conductivity), surface waves do not
play an important role. In that case height is the determining factor
(with high directivity in the horizontal plane). Polarization is of
less importance.

Best regards,

Wim
PA3DJS

  #4  
Old October 1st 07, 01:40 AM posted to rec.radio.amateur.antenna
Roy Lewallen
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Posts: 1,374
Default what homebrew HF antenna produces the most groundwave?

Wim mentioned the high angle lobe you get with a 5/8 wave antenna. It
produces a sky wave which can, if skip conditions are present, interfere
with the ground wave signal and cause fading. This could be a very
common and serious problem at higher frequencies where the ground wave
is weaker and the sky wave stronger. You can reduce this by keeping the
radiator height to 1/2 wavelength or less. Antennas in that height range
don't have a high angle lobe, although they do produce some radiation at
high angles. Radiators near a half wavelength in height produce less
high angle radiation than shorter antennas, and they have more
horizontal gain, so I'd think they would be best. I'm sure the AM
broadcasters have other "anti-fading" techniques -- other newsgroup
contributors would know much more about them than I do.

Roy Lewallen, W7EL
  #5  
Old October 1st 07, 05:36 PM posted to rec.radio.amateur.antenna
K7ITM
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Posts: 643
Default what homebrew HF antenna produces the most groundwave?

On Sep 30, 5:40 pm, Roy Lewallen wrote:
Wim mentioned the high angle lobe you get with a 5/8 wave antenna. It
produces a sky wave which can, if skip conditions are present, interfere
with the ground wave signal and cause fading. This could be a very
common and serious problem at higher frequencies where the ground wave
is weaker and the sky wave stronger. You can reduce this by keeping the
radiator height to 1/2 wavelength or less. Antennas in that height range
don't have a high angle lobe, although they do produce some radiation at
high angles. Radiators near a half wavelength in height produce less
high angle radiation than shorter antennas, and they have more
horizontal gain, so I'd think they would be best. I'm sure the AM
broadcasters have other "anti-fading" techniques -- other newsgroup
contributors would know much more about them than I do.

Roy Lewallen, W7EL


One way to get more ground wave without introducing the high lobes is
to use a collinear vertical. Just how practical this is depends on
the frequency of operation and what you have to hold the antenna up.
For example, on 30MHz, you could pretty reasonably put a half-wave
above a half-wave or above a quarter wave. On 3.5MHz, that would be
much more difficult for most of us. Even on 20 meters, you might be
able to do a collinear vertical. I suppose that MW AM broadcasters
are unlikely to use a vertical collinear, but maybe one of the other
contributors with lots of broadcast antenna experience could comment
on that.

Cheers,
Tom

  #6  
Old October 1st 07, 06:47 PM posted to rec.radio.amateur.antenna
Richard Fry
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Posts: 436
Default what homebrew HF antenna produces the most groundwave?

"K7ITM" wrote
I suppose that MW AM broadcasters are unlikely to use a
vertical collinear, but maybe one of the other contributors
with lots of broadcast antenna experience could comment
on that.

___________

Almost all US AM broadcast stations use non-sectionalized vertical
monopoles, but a few use a form of the Franklin antenna comprised
of two collinear, end-fed verticals.

The current thought on this in broadcast circles is that the additional
h-plane gain that provides over a 195-degree non-sectionalized
monopole isn't worth the initial cost and the continuing need to check
and adjust the power division and phasing between the sections of
a Franklin.

RF
  #7  
Old October 1st 07, 08:10 PM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default what homebrew HF antenna produces the most groundwave?

Anonymous wrote:
"Of all the HF antennas one might reasonably make out of wire or
aluminum tubing, which produces the strongest groundwave?"

Vertical antennas make the strongest groundwaves.

Assuming you are confined to a single ground-mounted element of
reasonable height and complexity, Kraus in the 3rd edition of "Antennas"
gives a simple answer in Figure 16-35 on page 569. A 0.64-wavelength
tall vertical radiator produces the greatest field strength at one mile
in the direction of the horizon.

Best regards, Richard Harrison, KB5WZI

  #8  
Old October 1st 07, 08:46 PM posted to rec.radio.amateur.antenna
Richard Fry
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Posts: 436
Default what homebrew HF antenna produces the most groundwave?

"Richard Harrison" wrote
Kraus in the 3rd edition of "Antennas" gives a simple answer
in Figure 16-35 on page 569. A 0.64-wavelength tall vertical
radiator produces the greatest field strength at one mile
in the direction of the horizon.

_____________

....and subparts (c) and (e) of that figure clearly show the high-angle
sidelobe centered at about 58 degrees elevation from an 0.64-lambda monopole
that may cause self interference -- per Roy Lewallen's post earlier in this
thread.

RF


  #9  
Old October 2nd 07, 10:58 PM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default what homebrew HF antenna produces the most groundwave?

Eichard Fry wrote:
"...and subparts (c) and (e) of that figure clearly show the high-angle
sidelobe cebtered at about 58 degrees elevation from an 0,64-lambda
monopole that may cause self interference..per Roy Lewallen`s post
earlier in this thread."

All too true. In AM broadcasting, at night the sky wave may interfere
with the ground wave beyond the skip zone.

In HF transmissions, the ground wave is likely exhausted in short order
so that the sky wave is the only signal available at considerable
distances. There will be no ground wave to beat with the sky wave to
cause fading but there are numerous paths for the sky wave which produce
plenty of fading without adding any ground wave to the mix.

Best regards, Richard Harrison, KB5WZI

 




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