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 Fan dipole spacing 
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Post Fan dipole spacing
Hi All,
Yesterday I built a fan dipole for 80 / 40m. The 80m is working well, but the 40m will sometimes tune up, then sometimes will not, I will check all the connections in the morning.

I have used bamboo to space the wires using just 7 inches, so my question is, is 7 inches to close ?, if so what would be the best ?

I am considering building the mk2 version with top band this time, so would be keen to get the spacing spot on.
Cheers
Geoff mw0ati

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Wed Apr 11, 2012 10:14 pm
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 Fan dipole spacing 
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Can you splay the ends of the 40m dipole further away from the big dipole?

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Wed Apr 11, 2012 10:23 pm
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 Fan dipole spacing 
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I followed some pictures I found on the web, so wrapped the 40m end over the wire of the 80m dipole, so I think it may be touching and shorting out the 40 dipole?, but this does not explain why I have a 1:1 vswr on 3,7mhz but for peace of mind I will re jig in the morning the 40m dipole termination

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Wed Apr 11, 2012 10:35 pm
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Post Re: Fan dipole spacing
I bet if you look closely at the picture, that the final part of the 40 dipole (between the last piece of boo and the 80 dipole) is actually string.

I'd try to spread the last few meters away. Might make the tuning a bit less touchy too.

Good Luck.

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Wed Apr 11, 2012 10:43 pm
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 Fan dipole spacing 
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Post Re: Fan dipole spacing
mw0ati wrote:
I followed some pictures I found on the web, so wrapped the 40m end over the wire of the 80m dipole, so I think it may be touching and shorting out the 40 dipole?, but this does not explain why I have a 1:1 vswr on 3,7mhz but for peace of mind I will re jig in the morning the 40m dipole termination


Possibly because RF is seeing the 40m element as part of the 80m electrically length but the same can't be said for the shorter dipole.
When you get to the lower bands interaction becomes more prominent because of the separation distance in terms of wavelength, 7" isn't really enough.
Add the 160m dipole alongside and the 80m reading will probably also go haywire but 160 will remain constant, in this instance both other electrical lengths will become incorporated into the electrical length of 160.......that's my take on it, but the man who will definitely know will be around soon. ;)

btw, if it were me I think I'd looked at a trapped dipole, I think someone on this forum was turning out the traps a while back.

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Wed Apr 11, 2012 10:44 pm
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 Fan dipole spacing 
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ei9ju wrote:
I think someone on this forum was turning out the traps a while back.


Mark 2W0JMK is the chap you're thinking of Gerry.

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Wed Apr 11, 2012 11:18 pm
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 Fan dipole spacing 
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JohnG7SSE wrote:
ei9ju wrote:
I think someone on this forum was turning out the traps a while back.


Mark 2W0JMK is the chap you're thinking of Gerry.


Yip that's the man, and they looked very well made will solidified resin covering the important bits ;)

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Wed Apr 11, 2012 11:31 pm
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Post Re: Fan dipole spacing
mw0ati wrote:
I followed some pictures I found on the web, so wrapped the 40m end over the wire of the 80m dipole,


You built it wrong. The 40m end goes nowhere near the 80m. The spacing is maintained throughout and the only thing the 40m end should do is finish or hang down a bit.

As someone else has said, it looks like you mistook the string used to keep the tenstion on the elements for the antenna wire.

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Wed Apr 11, 2012 11:53 pm
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 Fan dipole spacing 
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Post Re: Fan dipole spacing
Yep, its looking more and more that I built it wrong, so will sort out the 40m termination in the morning and see how I get on, thanks all for the help / input.
73
Geoff mw0ati

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Wed Apr 11, 2012 11:58 pm
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 Fan dipole spacing 
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Post Re: Fan dipole spacing
ei9ju wrote:
.......that's my take on it, but the man who will definitely know will be around soon. ;)

You all got there before me !

Just a few points:

1) You can get the dipoles very close together and the antenna will still work fine - some folk even use ribbon cable for the elements; however, the band interdependence gets worse as the wires get closer together, so with several bands you better be patient when it comes to tuning :)

2) Because the band interaction increases with smaller spacing, the more important it becomes to make sure that spacing doesn't vary as the dipole moves around with the wind.

3) It's the high voltage areas at the ends of the dipoles where the interaction is at its highest, so anything you can do to increase the wire spacings at the ends of the individual dipoles will help.

73,
Steve G3TXQ


Thu Apr 12, 2012 7:29 am
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 Fan dipole spacing 
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Post Re: Fan dipole spacing
Thanks Steve, I will have a look at the 40m ends and alter the termination and see how I get on.
73
Geoff

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Thu Apr 12, 2012 7:43 am
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Bwlchgwyn.

That's easy for you to say .....

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Thu Apr 12, 2012 8:00 am
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 Fan dipole spacing 
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In english it translates to "White Pass", it's the highest village in Wales at approx 1100 to 1200 ft asl, very handy if radio is your hobby :D

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Thu Apr 12, 2012 10:09 am
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Post Re: Fan dipole spacing
G3TXQ wrote:
3) It's the high voltage areas at the ends of the dipoles where the interaction is at its highest, so anything you can do to increase the wire spacings at the ends of the individual dipoles will help.

73,
Steve G3TXQ


The usual way to address that when using ribbon cable and the like is to leave the last foot or two hanging down vertically.

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Thu Apr 12, 2012 10:26 am
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mw0ati wrote:
In english it translates to "White Pass", it's the highest village in Wales at approx 1100 to 1200 ft asl, very handy if radio is your hobby :D


Same here. If you QRZ the hams in Whitehaven, half of them live in one place: 'Hillcrest'.

How u getting on with the fan?

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Thu Apr 12, 2012 11:51 am
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