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ranger140 Profile
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Freebander

Registered: 03-2010
Posts: 73
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di-pole into a 2 element beam


I have my hands on a sirio di-pole.
I was thinking of adding a pole to turn it into a 2 element beam for portable work,
however best to go for the director or the reflector??
I am also not sure if the boom supplied with the di-pole is long enough to seperate the two, I have had conflicting advice on distances between them, any thoughts please.
Thanks.

T
5/Oct/2011, 12:44 pm Link to this post Send Email to ranger140   Send PM to ranger140
 
yamanx1 Profile
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Head Honcho

Registered: 09-2007
Location: In a world of my own
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Re: di-pole into a 2 element beam


Best way is to have two driven elements, using 70ohm coax between the two elements, I have some plans for this, I’ll post them.

Or turn it into a three element, the spacings are quite close for the Sirio three element. But you will need a slightly longer boom and the ali pole is a difficult diameter to get hold of, although I have some here you can have 

Either way you will need the small casting that comes with the Sirio for best results.


---

By all means think yourself big, but never think others small.... R.F.Scott
5/Oct/2011, 2:18 pm Link to this post Send Email to yamanx1   Send PM to yamanx1
 
Hot Fusion Profile
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Management

Registered: 03-2008
Location: South West England
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Re: di-pole into a 2 element beam


I believe adding either a director or reflector have similar benefits, so the choice is up to you.

bear in mind that a reflector needs to be approx. 5% longer than the driven element, and a director needs to be about 5% shorter.

Also note that the feedpoint impedance will drop quite a bit meaning you will no longer get a good match to the coax and this may well cost you as many decibels as any you would gain from the modification.

My honest advice would be to get a purpose-built 3 element antenna - this will have the correct spacings and element lengths, and have a feedpoint matching section.

---
Andy - FB107
8/Oct/2011, 5:50 pm Link to this post Send Email to Hot Fusion   Send PM to Hot Fusion
 
mikefox whiskey Profile
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Accomplished DX-er

Registered: 02-2009
Location: Northern Ireland
Posts: 403
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Re: di-pole into a 2 element beam


I was thinking of turning my Sirio SD27 dipole also into a two element beam, the boom is 4ft 7 inches or thereabouts, the British built Vortex two element beams have a similar length boom.

I was going to add a reflector behind the driven element, this would be good for front to back rejection, adding a director in front rather than a reflector would perhaps have more gain but less rejection from signals to the rear, it's all about experimentation with the spacing and a good antenna analyser would be handy.

I was contemplating actually adding a piece of boom and making a three element out of it, spacing's are widely different on commercially made beams and I guess I would have to play about, for instance the Maco M103 three element is 11ft long with 7ft between the reflector and driven with 4 ft between the driven and the director.

The 3 element sirio equivalent has an 8 or 9ft boom, with 4ft between the elements.

So plenty of scope for messing about with differing lengths.


---
(Forum user name is now SuperNasty)
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topbuzzuk Profile
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Big Cheese

Registered: 11-2007
Location: Wiltshire, UK
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Re: di-pole into a 2 element beam


dave are you on about co-phasing the two di-poles? i'd like to se the plans for that, but i imagine its pretty simple just the spacing and length of the two bits of 70-75ohm coax??

---
26FB118
2/Dec/2011, 7:21 pm Link to this post Send Email to topbuzzuk   Send PM to topbuzzuk Yahoo
 
henry hpsd Profile
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New Kid On The Block

Registered: 02-2010
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Re: di-pole into a 2 element beam


Hello,

It is known that it is possible to construct a 2elements yagi with relative short spacing and actually getting that way maximum gain...
You can also make the antenna and tune it for maximum front to back.
A "study" on the www.cebik.com website will provide better information than i can tell.

HOWEVER...

And thats a big however.
That "maximum" is only over a relative short bandwidth.

Possibly the best way to go for the average CB user would be to go for a 2 elements moxon.
The moxon will have a not noticable slightly lower gain (in comparisment to a maximum gain 2elements yagi-uda antenna)
But it will remain rather high over a wider bandwidth which is a major bennefit as the CB band is rather wide.

Besides the 2el moxon has a direct 50 ohms impedance for that reason there are no matching losses (as small as that migth be)

We could do another thing.
I have designed a 3elements folded dipole yagi with a 6 feet boom.
That antenna has a antenna plot which never has been seen before on 11 meter
(for that boomlength).
And it is also 50 ohms so relative easy to feed.
If you are interested please mail me as im more than willing to help you.
(i wont put the link online as we sell them commercial aswell and i dont want to give the wrong impression)

By the way you do have another option:
You migthdo a google search on "jungle job" antenna. Im more than willing to desing that for you aswell.
It looks like a bow and arrow. Where the bow is the refelector. So..all you need is about 18 feet copper wire and some non-conducting wire for the attachment.


Hope it helped,

Kind regards,

Henry 19SD348
4/Dec/2011, 8:00 pm Link to this post Send Email to henry hpsd   Send PM to henry hpsd
 
ranger140 Profile
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Freebander

Registered: 03-2010
Posts: 73
Karma: 1 (+1/-0)
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Re: di-pole into a 2 element beam


sorry haven;t been around alot,
Thanks for your your replys.
I am waiting for some better 'summer' weather to get back out portable.

I am not really the 'aerial type' but i would like to give this a go very soon.

t
28/Dec/2011, 7:29 pm Link to this post Send Email to ranger140   Send PM to ranger140
 
sydthecat Profile
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Freebander

Registered: 02-2012
Posts: 21
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Re: di-pole into a 2 element beam


hi all

I had a two element yagi made for me by a friend of a freind and i must say it really does work well

Image

Image

Image

Cheers Craig
22/Jun/2012, 2:42 pm Link to this post Send Email to sydthecat   Send PM to sydthecat Blog
 
Kaosss Profile
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Management

Registered: 04-2008
Location: County of Flintshire, N. Wales
Posts: 1890
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Re: di-pole into a 2 element beam


Yes indeed, I can vouch for that, it does work very well. Nice one Craig
Al

---
Al -163FB777 - N.Wales, UK
Kenwood TS-480SAT, TS590, MC-90, Yaesu FT1000D, FT2000D,RCI 2995dx, Heil 781, 5 eli beam, F/S G5RV, K40 when mobile, A99 for portable. Optima V3,Portapack. RM KL500-modded, PMR`s.Ranger 1k Amp
22/Jun/2012, 6:27 pm Link to this post Send Email to Kaosss   Send PM to Kaosss Blog
 
SuperNasty Profile
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Freebander

Registered: 01-2012
Location: NI
Posts: 59
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Re: di-pole into a 2 element beam


Looks good that 2 element with the hairpin match, I have since bought a 2 element Moxon from Henry at HPSD antennas and am very pleased with it, extremely high front to back ratio for rejection and enough gain to get good reports, easy to put together and light weight though heavy duty. Henry does not want to plug his commercial business on the forum but as a buyer I can recommend him 100%.

http://www.hpsd.nl/

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(Forum user name was previously - mikefox whiskey) - 68 FB750 - Pat

Kenwood TS870 - Centre fed balanced dipole - HPSD 2 element Moxon for 11m, vertical 'Ringo' for 11m.
22/Jun/2012, 9:10 pm Link to this post Send Email to SuperNasty   Send PM to SuperNasty Blog
 


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