Antenna too long??
 

I am trying to put up a dipole for 40 m. The formula calls for about 65
feet.

Between my tress I easily have space for twice that.

That would still resonate, would it not.

Tell me that longer is better, at least when it comes in multiples.






73 Uwe

66 feet 4 inches drops you in the middle of 40 metre band.

33 feet 2 inch a leg.

Between trees is better than through them.
Re check everything, when the leaves are on the trees.

QRP HomeBuilder web site is at

http://qrp.pops.net/qrp/default.htm

They have dipole antenna software for free.

Best of luck

Uwe,
'Bigger/longer' isn't necessarily 'better'! A longer
dipole -may- resonante on the desired frequency, but the
65 feet (approximate) is really all you need. Twice that
length would probably work for you, but feeding it in the
center would also be a very bad impedance match for 50 ohm
coax. Not to mention will produce a radiation pattern
different from what you might expect. A full wave, instead
of a 1/2 wave, dipole can be made to work, but all things
considered, why bother?
'Doc

On Thu, 15 Apr 2004 06:31:41 -0500, 'Doc wrote:

Not to mention will produce a radiation pattern
different from what you might expect.

Oh, and just how different would the pattern be?

Danny, K6MHE

Uwe wrote:
I am trying to put up a dipole for 40 m. The formula calls for about 65
feet.

Between my tress I easily have space for twice that.

That would still resonate, would it not.

If you say a 6000 ohm feedpoint is resonant. I personally call that
the (anti)resonant point.

Tell me that longer is better, at least when it comes in multiples.

You will be able to use the longer dipole on 75m. It will be about
one-wavelength long on 40m which gives some broadside gain over a
1/2WL dipole. But the feedpoint impedance on 40m will be so high
you will need to avoid coax and feed it with some variation of
ladder-line.
--
73, Cecil http://www.qsl.net/w5dxp



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Dan Richardson wrote:

On Thu, 15 Apr 2004 06:31:41 -0500, 'Doc wrote:
Not to mention will produce a radiation pattern
different from what you might expect.

Oh, and just how different would the pattern be?

A one-wavelength dipole has about 2 dB gain over a 1/2WL
dipole at the expense of other directions assuming a
height of 1/2WL+.
--
73, Cecil http://www.qsl.net/w5dxp



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Dan,
It's green instead of the 'normal' blue...
'Doc

On Thu, 15 Apr 2004 17:39:32 -0500, 'Doc wrote:



Dan,
It's green instead of the 'normal' blue...
'Doc

I fail to see that answers my question. Which was and is just how is
the pattern of a ½-wave dipole different than a full-wave dipole?

I know the answer, base upon you response to the original question I
wonder if you do.

However, because of you refusal to include the portion of the previous
message that you responding too in your postings (normal N/G
etiquette) it is difficult to be sure what you are talking about.

Danny

"'Doc" wrote in message ...


Uwe,
'Bigger/longer' isn't necessarily 'better'! A longer
dipole -may- resonante on the desired frequency, but the
65 feet (approximate) is really all you need. Twice that
length would probably work for you, but feeding it in the
center would also be a very bad impedance match for 50 ohm
coax.

The impedance will still be 50-to-70 ohms if you add the extra
half-wavelength to just one end of the antenna.
i.e. The wire on one side of the antenna feed point (coax connection) is
still 32.5 feet, and the wire on the other side would be 65' + 32.5' plus
another 3.3', since there is no end-effect on the extra half-wavelength of
wire you are adding. So actually, one side is 32.5 feet and the other side
is 100.8 feet. You should get almost 2 db of gain in four directions (a
"cloverleaf") by doing that. You will also get a significant reduction in
signal strength (a "null") broadside to the antenna and off the ends. I used
a dipole like that for years in Florida where one of the gain lobes was NE
and the nulls cut out a lot of the stateside QRM for me during European
contests. The full-wave dipole was up about a half-wavelength (65 feet), so
I used RG59 (75 ohm) coax instead of RG58 (50 ohm) coax, and had a good
match. No balun was needed.

Andy

"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message
...
On Thu, 15 Apr 2004 17:39:32 -0500, 'Doc wrote:

However, because of you refusal to include the portion of the previous
message that you responding too in your postings (normal N/G
etiquette) it is difficult to be sure what you are talking about.

He claims he doesn't know how to quote. I plonked him some time ago. Got
tired of trying to figure out what he was responding to. Would rather have
not done that as he does have useful information but his posting method is
just to cryptic.

King Zulu wrote:
The impedance will still be 50-to-70 ohms if you add the extra
half-wavelength to just one end of the antenna.

Actually, it may be closer to 100 ohms. It's an OCF somewhat like
a "Windom" fed with two-conductor transmission line. The "Windom"
is supposed to have a feedpoint around 300 ohms.

i.e. The wire on one side of the antenna feed point (coax connection) is
still 32.5 feet, and the wire on the other side would be 65' + 32.5' plus
another 3.3', since there is no end-effect on the extra half-wavelength of
wire you are adding.

It's an interesting OCF antenna but probably subject to common
mode currents unless an excellent choke is used at the feedpoint.

You should get almost 2 db of gain in four directions (a
"cloverleaf") by doing that.

Since it's a one-wavelength antenna, it won't quite achieve a
cloverleaf pattern. It's about the same gain as a 1/2WL dipole
(6 dBi) but with a much wider horizontal beamwidth. For a 130
ft. long antenna, the cloverleaf pattern develops around 10 MHz.
--
73, Cecil, W5DXP



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Dan & CW,
This may help understand 'how' I post, probably won't
excuse any percieved 'mistakes' in the procedure, but at
least you'll understand. I use a 'newsgroup' reader, it
shows each thread and each response in a thread, and
everything progrsses in a very logical manner. One of
these 'newsgroup' readers is provided in Netscape and IE.
I see no point in repeating what is already 'there' for
anyone to see (if they use a NGreader, of course). I have
to assume that you don't, too bad.
As for the radiation pattern differences between a 1/2
wave and full wave antenna, a specific explanation would
be kind'a difficult because more than the 'length' can make
a difference, height, environment, other antennas, etc.
But, in general, the usual higher angles of radiation are
more pronounced, and the pattern is 'sort of' sharper (if that
makes any sense) for the full wave dipole. It's easy to
see than to describe if you use a modeling program, or the
usual radiation pattern diagrams in the antenna books. This
also depends on the antenna's height, what I attempted to
describe
is at more than a 1/2 wave above ground. Being lower than a 1/2
wave above ground makes for even greater differences.
I hope that convinces you that I might have at least a faint
idea of what's happening...
'Doc

Andy,
True, for the most part. But I was 'assuming' a center
fed doublet, not an off center fed one. (To cover all the
possibilities would mean more 'work' than I'm willing to
put into a 'simple' answer.) Both of us are 'right'.
'Doc

PS - I used an antenna something like what you described at
one time. Fed with ladder line through a tuner, it loaded
like a dream on all bands! Had a really 'crappy' pattern
for the use I wanted to put it (couldn't rearrange how it
was errected), so I went back to the 'loop'. Oh well...

'Doc wrote:
This may help understand 'how' I post, probably won't
excuse any percieved 'mistakes' in the procedure, but at
least you'll understand. I use a 'newsgroup' reader, it
shows each thread and each response in a thread, and
everything progrsses in a very logical manner.

I use the Netscape newsreader but it is more convenient
for me to sort by date rather than by thread. Therefore,
I don't know to whom you are replying unless you quote
the attributions and understanding the context of
your postings is quite often difficult for me.
--
73, Cecil, W5DXP



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"Cecil Moore" wrote in message
...
King Zulu wrote:
The impedance will still be 50-to-70 ohms if you add the extra
half-wavelength to just one end of the antenna.

Actually, it may be closer to 100 ohms. It's an OCF somewhat like
a "Windom" fed with two-conductor transmission line. The "Windom"
is supposed to have a feedpoint around 300 ohms.

The FW dipole I used for years had a 1.2:1 SWR, fed with RG59 and no balun.


i.e. The wire on one side of the antenna feed point (coax connection)
is
still 32.5 feet, and the wire on the other side would be 65' + 32.5'
plus
another 3.3', since there is no end-effect on the extra half-wavelength
of
wire you are adding.

It's an interesting OCF antenna but probably subject to common
mode currents unless an excellent choke is used at the feedpoint.

Never saw an indication that the feed line was radiating. On my many dipole
versions, I have tried them with and without baluns. If the resonance of the
antenna didn't change with the balun in, I figured the balun wasn't needed.
On one, where the coax could not come off perpendicular to the dipole, the
balun did raise the resonance frequency - suggesting the feedline was
radiating without the balun in. That same W2AU balun caused havoc with TVs
in my neighborhood when I used it for ten meter operation. I assumed the
core was saturating and causing the harmonics. For that reason, I don't use
baluns just for good measure; only when I need the matching (4:1 baluns) or
when there is some indication that the feedline is radiating. Plus, baluns
add weight to the antenna, loss to the power, and are susceptible to weather
problems.

You should get almost 2 db of gain in four directions (a
"cloverleaf") by doing that.

Since it's a one-wavelength antenna, it won't quite achieve a
cloverleaf pattern. It's about the same gain as a 1/2WL dipole
(6 dBi) but with a much wider horizontal beamwidth. For a 130
ft. long antenna, the cloverleaf pattern develops around 10 MHz.
--
73, Cecil, W5DXP

The 2db gain was what the ARRL Antenna Book (1964 vintage, p. 142) was
calling out for a FW collinear array gain. Actually, the FW dipole fed at
the current node would be like a 1-wavelength long longwire (a short
longwire?), and the Antenna Book shows a negligible 1/2 db gain (p. 170 on
"Long-Wire Antennas") over the dipole gain. The cloverleaf assertion was
based the Antenna Book radiation patterns shown on p. 39 (Fig 2-16) and the
discussion of "How Patterns are Formed", as well as p. 59 (Fig 2-74b)
showing the FW pattern distortion caused by end feeding.

K4YKZ

King Zulu wrote:
The FW dipole I used for years had a 1.2:1 SWR, fed with RG59 and no balun.

It still may have had a feedpoint impedance of ~100 ohms. RG59's
Z0 is 75 ohms, close to what you would need to transform 100 ohms
to 50 ohms. An odd number of 1/4WLs of RG59 will transform 100 ohms
to 57 ohms, neglecting losses.

Never saw an indication that the feed line was radiating.

We can mount a logical argument that since the feedpoint
impedance looking in each direction is different, the
currents have to be unbalanced resulting in feedline
radiation.

The 2db gain was what the ARRL Antenna Book (1964 vintage, p. 142) was
calling out for a FW collinear array gain. Actually, the FW dipole fed at
the current node would be like a 1-wavelength long longwire (a short
longwire?), and the Antenna Book shows a negligible 1/2 db gain (p. 170 on
"Long-Wire Antennas") over the dipole gain. The cloverleaf assertion was
based the Antenna Book radiation patterns shown on p. 39 (Fig 2-16) and the
discussion of "How Patterns are Formed", as well as p. 59 (Fig 2-74b)
showing the FW pattern distortion caused by end feeding.

EZNEC says that it is somewhat of a square pattern where the "corners"
of the square are just barely starting to form a cloverleaf. The "nulls"
off the ends are only 3 dB down. I suspect there was a lot of guessing
about radiation patterns in 1964. Some say there still is a lot of
guessing. :-)
--
73, Cecil http://www.qsl.net/w5dxp

On Fri, 16 Apr 2004 08:07:34 -0500, 'Doc wrote:

Here, so all can see exactly what I am responding to:
[snip]
I use a 'newsgroup' reader, it
shows each thread and each response in a thread, and
everything progrsses in a very logical manner.
[snip]

I too use a reader as I believe everyone else does, however, rather
than clutter up my screen with old obsolete messages I us an option of
my reader that lists only the new unread messages.

Additionally, there are at times multiple replies to a thread and your
posting may be listed several messages below the one you are replying
to and it can be anyone's guess which one it was.

Thirdly, for anyone reading the news group archives and trying to
follow anything you have posted is near to impossible as the archive
listing can be by the poster and not the thread.

Lastly, news group etiquette was setup of a good reason. Following
those suggestions allows for a minimum of confusion.

Please think about this. Of course, if you just want to be contrary
then have fun.

73
Danny

"Cecil Moore" wrote in message
...
King Zulu wrote:
The FW dipole I used for years had a 1.2:1 SWR, fed with RG59 and no
balun.

It still may have had a feedpoint impedance of ~100 ohms. RG59's
Z0 is 75 ohms, close to what you would need to transform 100 ohms
to 50 ohms. An odd number of 1/4WLs of RG59 will transform 100 ohms
to 57 ohms, neglecting losses.

Never saw an indication that the feed line was radiating.

We can mount a logical argument that since the feedpoint
impedance looking in each direction is different, the
currents have to be unbalanced resulting in feedline
radiation.

The 2db gain was what the ARRL Antenna Book (1964 vintage, p. 142) was
calling out for a FW collinear array gain. Actually, the FW dipole fed
at
the current node would be like a 1-wavelength long longwire (a short
longwire?), and the Antenna Book shows a negligible 1/2 db gain (p. 170
on
"Long-Wire Antennas") over the dipole gain. The cloverleaf assertion was
based the Antenna Book radiation patterns shown on p. 39 (Fig 2-16) and
the
discussion of "How Patterns are Formed", as well as p. 59 (Fig 2-74b)
showing the FW pattern distortion caused by end feeding.

EZNEC says that it is somewhat of a square pattern where the "corners"
of the square are just barely starting to form a cloverleaf. The "nulls"
off the ends are only 3 dB down. I suspect there was a lot of guessing
about radiation patterns in 1964. Some say there still is a lot of
guessing. :-)

Well, the FW dipole may not have had all the advantages I thought it did -
but it worked well enough that I stopped bothering with the 2-element wire
beam on 40m for the contests. It's a bit like fishing - if you believe in
your equipment you will usually do better than if you don't. HI

K4YKZ

King Zulu wrote:
Well, the FW dipole may not have had all the advantages I thought it did -
but it worked well enough that I stopped bothering with the 2-element wire
beam on 40m for the contests. It's a bit like fishing - if you believe in
your equipment you will usually do better than if you don't. HI

It's not a bad antenna and I didn't mean to knock it. I like
that 40m pattern where it has 280 degrees of beamwidth. It's
actually better than a cloverleaf beamwidth pattern.
--
73, Cecil http://www.qsl.net/w5dxp