Hi Art

I'd say that every little bit helps when conditions are marginal. Even
10dB extra mean pretty well nothing in readability when the signal is
already 20dB above the noise, but a few dB *can* make a difference when
the signal is in noise.

I don't see that! would not the S/N stay the same?

Well to tell you the truth this was one of those "told by someone else"
things that I never did get around to proving myself (thinking it was
general knowledge) I have of course noticed it on 2M FM where the
recovered audio S/N falls off very rapidly as the usable senitivity of
the radio is reached. In that case a 1 or 2dB signal increase can make
the difference between readable 1 and readable 4. I have a funny feeling
the discussion I heard on the topic may have been on front end NF of
VHF/UHF receivers where a 1dB lower number there yielded a much larger
dB result. Note this was for SSB. I have some work to do here
understanding this. When I look at building another preamp for 2/70 I'll
do it then!

However if the noise is -110dBm and the signal was -114dBm, the margin
(s/n) would become less (of a negative number) when the signal level is
increased. You may not be able to resolve it but you can measure the
difference. You can of course use DSP techniques to resolve signals
weaker than noise. WRSS60 for example will enable you to resolve signals
26dB below the noise level. FSK441/JT44 is another example of signal
below noise reception.

For horizontal waves the ground conditions relative to 1 wavelength is of
little concern
Height as always helps with low TOA so one has to determine the average
incoming signal angle
of choice QSO's and design to suit.

Something about brewster angles and phase reversal in horizontal but not
vertical polarisation? (Note I work in IT, not RF!) I always thought
that the poorer the ground (eg sand/clay) the higher the takeoff angle
and over seawater was the lowest one could attain. (Keep in mind that VK
dropped CW earlier this year and I was one of those that has been
playing VHF+ for the last 25 years!)

Agreed but I would like to see smaller turning radius ( moving away
from the
boom length mantra , )
without the necessity for dual driven stacked array This would require a
fixed feed point with
moveable elements for desired TOA to suit desired QSO..

I would also expect that F/B & F/S are major contributors to design to.
Very handy when you neighbours son a few miles away wants to tune his VW
engine! I like the idea of a quad, simply because of its smaller turning
radius!

I once had a think about ways to tune a 3 element quad for best F/B.
Maybe some way to roll the wire up on a small motor shaft or tune it
with some C on the end of some tuned length feeder? Didnt figure out an
easy way to change the element spacing though. Maybe bending the
spreaders would have a similar effect of changing the feedpoint
positions on a stacked array?

You could also change the length of the phasing sections for a dual
driven stacked array - rather than moving the feedpoint. If I was
experimenting with this idea I'd probably start (modeling) with 3
parallel horizontal dipoles arranged such that when viewed from the ends
the (end point) shape was a triangle. All would be fed in parallel but
with different phase relationships between them.

I am sure it can be done, and since 'every thing is
known about antennas' all that is reguired is for a Guru to come forward to
share how it is done.

Not me sorry. If however I stumble onto something that defies all the
theory and works better than anyone else, this NG will be the first to
know - and I'll make the design like GPL software! Free...

Cheers Bob VK2YQA

I say ignore the TOA. (For those unfamiliar with the term, it's the
"takeoff angle", which usually means the elevation angle at which the
antenna pattern is strongest.)

What counts is the gain at the elevation angle at which you want to
communicate. This, in turn, depends on the distance and the propagation
conditions. If you need a strong signal at an elevation angle of 15
degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or
zero. All that counts is the gain at 15 degrees. And an antenna with TOA
of 15 degrees doesn't necessarily have the most gain at 15 degrees of
any antenna.

Consider the following three 40 meter antennas: A vertical antenna with
about 8 radials (18 ohm ground system resistance), a dipole at 30 feet,
and a dipole at 40 feet, all over average ground.

Antenna TOA deg Gain at 26 deg. Gain at 15 deg.

Vert 26 -1.76 dBi -2.72 dBi
Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi
Dipole @ 40' 51 3.9 dBi 0.32 dBi

-- Which one has the lowest takeoff angle?
-- Which one is the best for communicating at 26 deg. elevation angle?
-- Which one is the best for communciating at 15 deg. elevation angle?

What does the takeoff angle have to do with which antenna is best?

Roy Lewallen, W7EL

art wrote:
Most people have added an amplifier only to find out that the
difference in signal
was very small. Thus many people deride the value of a 'silly' db gain
whereas DX'ers say that a single db extra is a lot !
Fact is that most long distance signals on 20 metres come in at angles
of 11 degrees or less where as the 'normal' antenna has a TOA of around
14 degrees.
So where a dxer points to the extra 1db gain as being everything in
fact it is the lowering of the TOA that comes with the extra gain. In
my opinion if one designs his antenna for a lower TOA say 10 to 11
degrees then even tho its gain may well be below the dxers choise( a
very long boom or stacked antennas) the lower TOA with less gain will
show little difference
to the antenna of choics because the lower edge of the radiation lobe
will follow the same line and any extra gain provided will have the
same effect of adding an amplifier which is minimal compared to the
ability of capturing signals that arrive at low angles.
I believe it is time for antenna designers to concentrate less on
obtaining gain and instead concentrate more on lowering the TOA.
without the need of excessive real estate requirements.
What say ?
Art

On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:

What does the takeoff angle have to do with which antenna is best?


That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.


--
Buck
N4PGW

*Sigh*

I tried.

Roy Lewallen, W7EL

Buck wrote:
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:


What does the takeoff angle have to do with which antenna is best?



That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.

Roy Lewallen wrote:

*Sigh*

I tried.



Let me have a shot at it, Roy.

possible blather alert!

Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that low
TOA than a more efficient antenna with a higher TOA is at that same low TOA.

Oy.

- Mike KB3EIA -

rest snipped

Mike Coslo wrote:
Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that
low TOA than a more efficient antenna with a higher TOA is at that same
low TOA.

Maybe a picture is worth a thousand words. Here's a comparison
radiation pattern for my 130 ft dipole Vs my 40m vertical with
elevated radials. In the dipole's favored direction, it's TOA
is greater than the vertical's yet the dipole radiates more
power than the vertical even at the vertical's TOA. Here's the
pictu http://www.qsl.net/w5dxp/dipvsver.htm
--
73, Cecil, W5DXP


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Yes, you've got it. Hopefully some of the folks who didn't understand my
explanation will understand yours.

Roy Lewallen, W7EL

Mike Coslo wrote:

Let me have a shot at it, Roy.

possible blather alert!

Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that
low TOA than a more efficient antenna with a higher TOA is at that same
low TOA.

Oy.

- Mike KB3EIA -

rest snipped

On Fri, 28 Jan 2005 23:25:19 -0800, Roy Lewallen
wrote:

*Sigh*

I tried.

You can lead a horse to water.....


Roy Lewallen, W7EL

Buck wrote:
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:


What does the takeoff angle have to do with which antenna is best?



That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.

On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:

I say ignore the TOA. (For those unfamiliar with the term, it's the
"takeoff angle", which usually means the elevation angle at which the
antenna pattern is strongest.)

What counts is the gain at the elevation angle at which you want to
communicate. This, in turn, depends on the distance and the propagation
conditions. If you need a strong signal at an elevation angle of 15
degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or
zero. All that counts is the gain at 15 degrees. And an antenna with TOA
of 15 degrees doesn't necessarily have the most gain at 15 degrees of
any antenna.

Consider the following three 40 meter antennas: A vertical antenna with
about 8 radials (18 ohm ground system resistance), a dipole at 30 feet,
and a dipole at 40 feet, all over average ground.

Antenna TOA deg Gain at 26 deg. Gain at 15 deg.

Vert 26 -1.76 dBi -2.72 dBi
Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi
Dipole @ 40' 51 3.9 dBi 0.32 dBi

-- Which one has the lowest takeoff angle?
-- Which one is the best for communicating at 26 deg. elevation angle?
-- Which one is the best for communciating at 15 deg. elevation angle?

What does the takeoff angle have to do with which antenna is best?

Roy Lewallen, W7EL

Dear Roy,

3 cheers.


Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

Amen.
Let us use TOA for the elevation angle where an antenna's pattern is
strongest and ATOA for the actual elevation angle used over a long HF path.

At least from 7 MHz to 21 MHz, when DX ionosphere propagation is likely
the ATOA is between about 12 degrees and about 2 degrees. When comparing
antennas to be used for HF DX contacts, it is appropriate to note the gain
at 3, 6, and 9 degrees as being the numbers to compare. The actual TOA (as
defined above) is only interesting.

That said, it is possible to have a single horizontally polarized
antenna that is so high that it suffers in comparison to a lower antenna for
ATOAs of about 10 degrees (by more than the one db that is being talked
about). For one horizontally polarized antenna to be used for DX contacts
the desired heights are two to three wavelengths above earth.

If one can use a plurality of horizontally polarized antennas,
interesting results are possible. For instance: on receive, combining a
lower second antenna with a tall first antenna can effect the approximate
cancellation of the second lobe. The second lobe has a high TOA and can
contribute significantly to the noise and interference received from
relatively short distances. Nulling the second lobe can significantly
increase the received SNR.
For closer spacing of multiple antennas, one can effect more gain than
that of one antenna - with trade-offs.

I emphasize what has been said by Roy and others: TOA (as defined
above) is interesting, but it is not the most important number for DX
contacts.

73 Mac N8TT


--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Roy Lewallen" wrote in message
...
I say ignore the TOA. (For those unfamiliar with the term, it's the
"takeoff angle", which usually means the elevation angle at which the
antenna pattern is strongest.)

What counts is the gain at the elevation angle at which you want to
communicate. This, in turn, depends on the distance and the propagation
conditions. If you need a strong signal at an elevation angle of 15
degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or
zero. All that counts is the gain at 15 degrees. And an antenna with TOA
of 15 degrees doesn't necessarily have the most gain at 15 degrees of
any antenna.

Consider the following three 40 meter antennas: A vertical antenna with
about 8 radials (18 ohm ground system resistance), a dipole at 30 feet,
and a dipole at 40 feet, all over average ground.

Antenna TOA deg Gain at 26 deg. Gain at 15 deg.

Vert 26 -1.76 dBi -2.72 dBi
Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi
Dipole @ 40' 51 3.9 dBi 0.32 dBi

-- Which one has the lowest takeoff angle?
-- Which one is the best for communicating at 26 deg. elevation angle?
-- Which one is the best for communciating at 15 deg. elevation angle?

What does the takeoff angle have to do with which antenna is best?

Roy Lewallen, W7EL