YEP!!

Jack Twilley wrote:



Actually, my goal is for the antenna to be resonant at 7.150. If it's
resonant too low, then I need to shorten the wires even more, right?

On Tue, 23 Mar 2004 00:29:43 -0800, Jack Twilley
wrote:
Yes, but pursuing a match close to 1:1 and an impedance close to 50
ohms seems to be a reasonable pursuit, if I understand correctly.

Hi Jack,

This is an aspiration on par with monks seeking nirvana. The two
illustrate it is the path, not the destination that is meaningful.

There is a very clear point to be made that unless you elevate the
dipole, any 50 Ohm characteristic you observe will more ground loss
than radiation resistance. This is reasonable only in the sense of
ease of tuning and the reductio ad absurdum is bliss can be found in a
dummy load. Clipping the ends of the current structure do not lead to
increased benefit unless you shave your advantage in tenths of a dB.
To put that in perspective, unless you are a teenager, you and your
contacts couldn't possible hear any change below 1dB variation. To
force that perspective further, propagation variation through one QSO
easily varies by that much or more (unless we are talking line of
sight FM with full quieting).

73's
Richard Clark, KB7QHC

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"Richard" == Richard Clark writes:

Richard On Tue, 23 Mar 2004 00:29:43 -0800, Jack Twilley
Richard wrote:
Yes, but pursuing a match close to 1:1 and an impedance close to 50
ohms seems to be a reasonable pursuit, if I understand correctly.

Richard Hi Jack,

Richard This is an aspiration on par with monks seeking nirvana. The
Richard two illustrate it is the path, not the destination that is
Richard meaningful.

Richard There is a very clear point to be made that unless you
Richard elevate the dipole, any 50 Ohm characteristic you observe
Richard will more ground loss than radiation resistance. This is
Richard reasonable only in the sense of ease of tuning and the
Richard reductio ad absurdum is bliss can be found in a dummy load.

Oh, I see your point here. What you're saying is that my dipole is so
far from the ideal that reaching 50 ohms won't mean anywhere near the
same thing that it does to the ideal case. That begs the question,
then -- if not 50 ohms, what is the best value for my particular
configuration?

Richard Clipping the ends of the current structure do not lead to
Richard increased benefit unless you shave your advantage in tenths
Richard of a dB. To put that in perspective, unless you are a
Richard teenager, you and your contacts couldn't possible hear any
Richard change below 1dB variation. To force that perspective
Richard further, propagation variation through one QSO easily varies
Richard by that much or more (unless we are talking line of sight FM
Richard with full quieting).

I've listened to QSOs where they've ebbed down to the noise floor and
flooded back several times over the course of a minute, so I
understand what you're saying.

Richard 73's Richard Clark, KB7QHC

I am really interested in knowing what sort of target values would
represent an optimal configuration, if that's at all possible.

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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On Tue, 23 Mar 2004 13:34:38 -0800, Jack Twilley
wrote:
Oh, I see your point here. What you're saying is that my dipole is so
far from the ideal that reaching 50 ohms won't mean anywhere near the
same thing that it does to the ideal case. That begs the question,
then -- if not 50 ohms, what is the best value for my particular
configuration?

I am really interested in knowing what sort of target values would
represent an optimal configuration, if that's at all possible.

Jack.

Hi Jack,

For the height you are at, you are probably already at the optimal
solution. If you could optimize further, at this height, it would
barely eke out 1dB difference. Ground dominates your design.

This is a heresy with dipole aficionados, but building a ground screen
will help toward the quickest, easiest 1dB return. You don't have to
do anything but shallow bury copper for the length of dipole + 20% and
maybe a quarter wavelength wide, beneath it. It need not attach to
anything to be beneficial. A grid of wires, 1M on a side is a good
first step.

You will undoubtedly note a tuning change, use a tuner to adjust (you
need it anyway). Some may distract you pointing out that it simply
sends more signal up. True, but as a screen, it removes loss, and
allows more signal out toward the horizon too.

73's
Richard Clark, KB7QHC

Jack Twilley wrote:

. . .
Frequency Resistance Reactance Impedance
7.00 14 6 15.2
7.05 18 15 23.4
7.10 18 21 27.7
7.15 21 20 29.0
7.20 24 27 36.1
7.25 28 36 45.6
7.30 28 43 51.3

. . .

The impedance is well within a 2:1 match throughout the voice segment,
and a 3:1 match across the entire band.

Assuming a 50 ohm system, the SWR for each of your impedances is shown
in the SWR column below. You might want to review how SWR is calculated
-- the ARRL Antenna Book is a good source.

Frequency Resistance Reactance Impedance SWR
7.00 14 6 15.2 3.63
7.05 18 15 23.4 3.06
7.10 18 21 27.7 3.33
7.15 21 20 29.0 2.83
7.20 24 27 36.1 2.82
7.25 28 36 45.6 2.93
7.30 28 43 51.3 3.37

Roy Lewallen, W7EL

"Jack Twilley" wrote in message
...
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"Richard" == Richard Clark writes:

Richard On Tue, 23 Mar 2004 00:29:43 -0800, Jack Twilley
Richard wrote:
Yes, but pursuing a match close to 1:1 and an impedance close to 50
ohms seems to be a reasonable pursuit, if I understand correctly.

Richard Hi Jack,

Richard This is an aspiration on par with monks seeking nirvana. The
Richard two illustrate it is the path, not the destination that is
Richard meaningful.

Richard There is a very clear point to be made that unless you
Richard elevate the dipole, any 50 Ohm characteristic you observe
Richard will more ground loss than radiation resistance. This is
Richard reasonable only in the sense of ease of tuning and the
Richard reductio ad absurdum is bliss can be found in a dummy load.

Oh, I see your point here. What you're saying is that my dipole is so
far from the ideal that reaching 50 ohms won't mean anywhere near the
same thing that it does to the ideal case. That begs the question,
then -- if not 50 ohms, what is the best value for my particular
configuration?

.................................................. ...........................
....................
Jack,
You may have a misconception about impedance here. Making the antenna
resonant is not going to make it 50 Ohms. Extrapolating your numbers, it
looks like resonance would be at around 6.9 MHz, and give you an impedance
of something like 12 + j0. Might be a good match to a 1:4 (not 4:1) balun,
but you would have to see what happens on the other bands.

Tam/WB2TT

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"Jack" == Jack Twilley writes:

Jack Over the next couple of days, I'll take some careful
Jack measurements of the antenna, its supports, and the distance of
Jack everything from the back of the house. The house was built in
Jack the 1940s and was constructed with wood and concrete with a
Jack stucco finish.

http://www.twilley.org/~jmt/antenna/dipole.html

The only thing I'm missing because I didn't think to measure it was
how long the individual dipole legs are. However, they started off as
the normal lengths for a full-length 40m dipole and inverted vees for
20m and 10m, as mentioned in the page. Tomorrow I'll go out and
measure the wires and update the text and the relevant drawing with
that information.

Tam, if you do model this antenna, I'd really appreciate it if you
shared the model with me as I've always wanted to learn more about
nec4 and friends but never really had the ability to get past the
punch-card mindset of the input files, and having my own antenna
modeled would probably do it.

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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En Tam/WB2TT va escriure en Tue, 23 Mar 2004 20:08:18 -0500:

Jack,
You may have a misconception about impedance here. Making the antenna
resonant is not going to make it 50 Ohms. Extrapolating your numbers, it
looks like resonance would be at around 6.9 MHz, and give you an impedance
of something like 12 + j0. Might be a good match to a 1:4 (not 4:1) balun,
but you would have to see what happens on the other bands.

Tam/WB2TT

Just a silly thought: If he made it resonant and had, indeed, 12
ohms, couldn't he make it into a folded dipole giving 12x4=48
ohms and probably a better bandwidth? (Of course this is assuming
monoband operation)

EA3FYA - Toni

En Toni va escriure en Wed, 24 Mar 2004 08:15:16 +0100:

En Tam/WB2TT va escriure en Tue, 23 Mar 2004 20:08:18 -0500:

Jack,
You may have a misconception about impedance here. Making the antenna
resonant is not going to make it 50 Ohms. Extrapolating your numbers, it
looks like resonance would be at around 6.9 MHz, and give you an impedance
of something like 12 + j0. Might be a good match to a 1:4 (not 4:1) balun,
but you would have to see what happens on the other bands.

Tam/WB2TT

Just a silly thought: If he made it resonant and had, indeed, 12
ohms, couldn't he make it into a folded dipole giving 12x4=48
ohms and probably a better bandwidth? (Of course this is assuming
monoband operation)

EA3FYA - Toni

Oops,

Just read in a previous post he is using a fan dipole. Don't
think it is possible to use the folded dipole then.

EA3FYA - Toni

"Toni" wrote in message
...
En Toni va escriure en Wed, 24 Mar 2004 08:15:16 +0100:

En Tam/WB2TT va escriure en Tue, 23 Mar 2004 20:08:18 -0500:

Jack,
You may have a misconception about impedance here. Making the antenna
resonant is not going to make it 50 Ohms. Extrapolating your numbers, it
looks like resonance would be at around 6.9 MHz, and give you an
impedance
of something like 12 + j0. Might be a good match to a 1:4 (not 4:1)
balun,
but you would have to see what happens on the other bands.

Tam/WB2TT

Just a silly thought: If he made it resonant and had, indeed, 12
ohms, couldn't he make it into a folded dipole giving 12x4=48
ohms and probably a better bandwidth? (Of course this is assuming
monoband operation)

EA3FYA - Toni

Oops,

Just read in a previous post he is using a fan dipole. Don't
think it is possible to use the folded dipole then.

EA3FYA - Toni

Toni,
I think you are right. Seems like the 40m folded dipole should be a short
circuit at 20. For a single dipole though, what you say makes sense (to me).

Tam/WB2TT