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Old January 6th 04, 04:00 PM
Ken Bessler
 
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Default Stupid question G5RV

I'm planning on putting up a MFJ G5RV antenna on the
flat roof of my 3 story apt building. I will be putting it up
as an inverted V on a 10 foot mast. Can't go any higher
do to landlord restrictions (hey - at least he's letting me
put the thing up - nice guy).

Problem is that the building is only 54x40 so the ends
of the G5RV will hang off the roof, half square style.

I've got trees and a tall fence outside the building that
can support the ends of the antenna but that would
mean bending the G5RV horizontally (tree NW of the
building, fence NE of the building)......

Question is should I use the supports or keep the ant
straight and let the ends droop? Actually, only 1 end
would droop as I could use the tree for support on the
other end - there is just no support on the SE side.

I know, I know.......stupid question - I should know
better. :-)

Ken KG0WX



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Old January 6th 04, 05:42 PM
Stef
 
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I think, with your situation, you should not put up a G5RV. Because
it needs a vertical portion of about 32 ft straight up for the flat
line. Unless you planned to let the flat line go straight down on the
side of the building, a bit away from the walls (18 inches ?) .

You should try to put up a 130 ft wire dipole instead, with a balun,
good coax and a tuner. Then you can do whatever you please with the
ends of the wire.

Can you put your 10 ft support on one side of the building and attach
one end of the dipole to the other side of the building and the other
end in the tree ?
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Old January 6th 04, 06:12 PM
Cecil Moore
 
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Ken Bessler wrote:
I know, I know.......stupid question - I should know
better. :-)


Hi Ken, a lot of us answer our own similar questions
by modeling the antenna. A free demo version of EZNEC
is available at www.eznec.com
--
73, Cecil http://www.qsl.net/w5dxp



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Old January 6th 04, 06:34 PM
Ken Bessler
 
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"Stef" wrote in message
...
I think, with your situation, you should not put up a G5RV. Because
it needs a vertical portion of about 32 ft straight up for the flat
line. Unless you planned to let the flat line go straight down on the
side of the building, a bit away from the walls (18 inches ?) .

You should try to put up a 130 ft wire dipole instead, with a balun,
good coax and a tuner. Then you can do whatever you please with the
ends of the wire.

Can you put your 10 ft support on one side of the building and attach
one end of the dipole to the other side of the building and the other
end in the tree ?


So, an antenna such as the Van Gorden "All Bander" would be a
better choice? I have a tuner - LDG Z100 and I made a "Balun"
by making a 5" dia 12 turn coax choke. I kinda like the idea of
the all bander antenna because 1) it has more wire and 2) it has
a longer ladder line, allowing it to reach my window. That way,
my feedpoint would only be 7 feet from the tuner (less loss in
the rg-58 coax).

Ken KG0WX


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Old January 6th 04, 07:28 PM
Bob Miller
 
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On Tue, 6 Jan 2004 10:34:08 -0700, "Ken Bessler"
wrote:


"Stef" wrote in message
.. .
I think, with your situation, you should not put up a G5RV. Because
it needs a vertical portion of about 32 ft straight up for the flat
line. Unless you planned to let the flat line go straight down on the
side of the building, a bit away from the walls (18 inches ?) .

You should try to put up a 130 ft wire dipole instead, with a balun,
good coax and a tuner. Then you can do whatever you please with the
ends of the wire.

Can you put your 10 ft support on one side of the building and attach
one end of the dipole to the other side of the building and the other
end in the tree ?


So, an antenna such as the Van Gorden "All Bander" would be a
better choice? I have a tuner - LDG Z100 and I made a "Balun"
by making a 5" dia 12 turn coax choke. I kinda like the idea of
the all bander antenna because 1) it has more wire and 2) it has
a longer ladder line, allowing it to reach my window. That way,
my feedpoint would only be 7 feet from the tuner (less loss in
the rg-58 coax).

Ken KG0WX


The longest dipole you can put up, fed entirely with ladderline to
your coax choke/auto tuner, would probably be your best bet for a
multi-band antenna. Check the Wireman's web site for his dipole
antenna kit -- has all the pieces you need.

Bob
k5qwg



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Old January 6th 04, 07:53 PM
Richard Clark
 
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On Tue, 6 Jan 2004 10:34:08 -0700, "Ken Bessler"
wrote:
"Stef" wrote in message

snip
You should try to put up a 130 ft wire dipole instead, with a balun,
good coax and a tuner. Then you can do whatever you please with the
ends of the wire.

snip
I kinda like the idea of
the all bander antenna because 1) it has more wire and 2) it has
a longer ladder line, allowing it to reach my window. That way,
my feedpoint would only be 7 feet from the tuner (less loss in
the rg-58 coax).


Hi Ken,
7 feet is no virtue, and could easily be a problem. The loss of
RG-58 over a span of 10 times as much may seem like a lot, but only
amounts to less than 1dB at the low HF to less than 3dB at the high
end. Let's split the difference and call it 2dB when looking into a
matched condition. THIS is the only reason to have a tuned antenna,
because line losses increase with SWR.

If you run with a simple doublet (whatever stretch of a wire dipole
your supports can hold in the air), it is obvious that the concept of
tuned is a caprice of chance. It pays then to use ladder line where
the losses due to the certain SWR are lower (owing to the larger
conductors only).

Calling an antenna multibanded can be achieved through either building
traps along its length that variously shorten it at high frequencies
and lengthen it at lower frequencies (the interaction of these two
agendas and the proximity of ground can easily drive you crazy) -OR-
it can be achieved with large block letters in the advertising copy.
If you cannot erect the trapped doublet high enough, the results may
be identical to the one bought on the basis of its multi-colored bold
typeface ad - equally lossy.

Hence, draping these "multiband" antennas such that they approach the
ground forces you to employ a tuner to take up the slack. If you have
to use a tuner, you best use ladder line. If you are using ladder
line and a tuner, you don't need tuned antennas. If you don't need
tuned antennas, you don't need to drape the doublet where it
approaches the lossy ground. If you are hoping to erect a multiband
meaning it covers 160, you are describing an air cooled resistor.

You may note the circularity of this, or the chicken and egg problem.
The truth of the matter is that almost any combination of
tuned/untuned antenna, with ladder/coaxial line, into a tuner will
give you fairly good operation. Unless you are sitting at the feed
point 7 feet away. If you park your car in the living room, you would
have the benefit of a Faraday shield to protect you and your equipment
to overcoupling to the fields you are trying to transmit. However, if
you put some distance between you and that point, you obtain a square
law advantage. At 14 feet you and your gear are exposed to one
quarter the output. 28 feet away, and you are down to one sixteenth
the exposure.

Even at this distance, some Hams experience their gear locking up
(foldback even at low power) due to close proximity (this is all
wavelength based, 40M operation with this problem is a classic
complaint in this board). This is due more often than not to poor
choking at the feedpoint, but proximity comes in a close second.

73's
Richard Clark, KB7QHC
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Old January 6th 04, 09:23 PM
Cecil Moore
 
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Bob Miller wrote:
The longest dipole you can put up, fed entirely with ladderline to
your coax choke/auto tuner, would probably be your best bet for a
multi-band antenna.


Bob, that's not exactly good advice for someone living on 100 acres. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Old January 6th 04, 11:24 PM
Bob Miller
 
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On Tue, 06 Jan 2004 14:23:01 -0600, Cecil Moore
wrote:

Bob Miller wrote:
The longest dipole you can put up, fed entirely with ladderline to
your coax choke/auto tuner, would probably be your best bet for a
multi-band antenna.


Bob, that's not exactly good advice for someone living on 100 acres. :-)


I guess you county guys with all the acreage have to restain
yourselves, eh?

Bob
k5qwg

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Old January 7th 04, 09:04 PM
Stef
 
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Yes, it is a very good choice, BUT by all means, you have to attach
the ladder line directly to your tuner.

You can add more ladderline, if you can order one with the length of
ladderline you need.
The ladderline is not easy to install because it must not be near to
metal objects. And you may cause interference problems to your close
neighbors.

Like I was saying, since you live in an appartment building, a coax
feedline will be easier to install. You will also avoid interference
with the neighbors with some sort of a good choke balun (current
balun) that will prevent the coax shield from radiating.

A trap dipole, that is resonnant on some bands will also reduce
interference due to the feedline, because it will keep swr low on the
coax.

So, an antenna such as the Van Gorden "All Bander" would be a
better choice? I have a tuner - LDG Z100 and I made a "Balun"
by making a 5" dia 12 turn coax choke. I kinda like the idea of
the all bander antenna because 1) it has more wire and 2) it has
a longer ladder line, allowing it to reach my window. That way,
my feedpoint would only be 7 feet from the tuner (less loss in
the rg-58 coax).

Ken KG0WX


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Old January 7th 04, 09:10 PM
Stef
 
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Default

you understand I meant that the choke balun has to be in the center
of the dipole


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