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 40m 2 ele wire antenna 
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Post 40m 2 ele wire antenna
Does anyone have a starting point or point me in the direction of a calculator please. I want to attempt a fixed yagi on 40m

Cheers.


Wed Sep 07, 2016 9:22 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
http://amfone.net/Amforum/index.php?act ... tach=14574

This is a link to a project I read about. 2 ele delta loops which can be switched from reflecter to driven.

Hth


Wed Sep 07, 2016 10:16 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
Moxon, it's wire and best of all isn't 60 odd feet wide.

Look for Moxon antenna project site and there's an online Moxgen calculator, from memory the antenna will be 45ft-ish wide.

Cheers, Dave.


Thu Sep 08, 2016 2:47 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
There is very little difference between a full sized Quad loop and one that is two thirds sized provided it is side loaded with wire capacity hats at its voltage points.

There was a very interesting article published in RSGB Radcom many years ago where someone actually did some experiments comparing a 2m Quad and one that was 2/3rds sized with side capacity loading. The difference was very small. However, as with any loaded antenna bandwidth will be smaller.

An elegant solution for a 40m Quad would be to construct a 30m Quad (about 2/3rds size of a 40m one) and fit 30m traps at its voltage points (eg mid way down each vertical leg) with capacity end loading wires on the other side of the 30m traps either going across the Quad or two wires; one going upwards and the other going downwards spaced out from the vertical wire as the side loading wires.

This would provide dual band 30/40m operation; on 30m the traps isolate the end loading wires while on 40m they offer inductive reactance and load the system for 40m.

This idea was patented I believe by G3IMX and used on a 20/15m and 10m Quad kit that he sold in the 1960/70's.

I did a similar thing with a homebrew 2el 15m Quad; I loaded the sides of the driven element using 15m traps and end loading wires. It worked extremely well as a simple 1el Quad loop on 20m with excellent results.

Now that we are past the sunspot peak I feel 40, 30 and 20m will now start to carry more DX and a three band directional antenna on those bands would be very worthwhile.

73's Vince G3TKN


Tue Sep 13, 2016 5:39 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
I built a full size 40m quad loop using a pine tree for support and a 9m fibreglass fishing rod to support the top most corner with two rope guys pulling out the left and right corners of the diamond, the bottom of this diamond was about 10 ft above ground.

I tried this thing fed at the top and then at a side corner before finally as a delta loop so that the bottom flat side was slightly higher above ground.

The Poxy loop never worked any better than the dual 9m fishing rod dipole at 43ft that I had started out with in the same tree and it was only listening to some bastid G station up north singing the praises of his full size vertical that had misled me into wrongly believing it was the loop and not his molten hot amplifier doing all the work.

Having said that I persisted with a 17m inverted delta loop fed at the base, again 43ft and upwards with the two 9m poles in a V and that was brilliant, surprisingly pumping a mere 300 watts through it made it perform nearly as well as Tom's 40m vertical loop... :this:

Cheers, Dave.


Thu Sep 15, 2016 8:47 am
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
For a fixed wire beam yagi the following dimensions should get you in the "ball park";

Driven element - total span 66ft

Reflector 5% longer than driven element - total span 69ft 3ins

If you were to use a director then this would need to be 5% shorter than the driven element - total span 62ft 8ins.

I once erected a 2el inverted V fixed wire 40m yagi (spacing between driven and reflector 21ft) off a catenary going from 50ft to 40ft. The beam fired towards the lowest support.

The results were really quite outstanding despite relatively low height; very quiet receive with reasonable rejection of Eu signals; mine was firing SW on LP. Although the feed impedance on the driven element was lowered due to the reflector I was still able to feed it directly with 50 ohm coax via a 1:1 current mode choke balun with swr no worse than 2:1 from memory.

Without any doubt, this fixed wire 2el yagi was one of the best antennas I ever used on 40m. However, the major disadvantage was its fixed direction but a 2el is fairly broad and if fixed say "west" you should get adequate coverage from SW to NW.

73's Vince G3TKN


Fri Sep 16, 2016 5:28 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
Thanks guys for the information and all food for thought going forward. One key thing (Dohhhh!!!) I forgot to add was it would need to fit within a plot size of 15m x 15m. This is the size of my unit at work and so I was hoping to use 4/6 fishing poles to suspend wires above at about 7-10m above metal roof :scratch:

Using the dims from you Vince im somewhat short and in any case whats the distances on 2ele and 3ele between the wire elements ?

If only something like this >>http://www.eantenna.es/?attachment_id=1613 could be made in wire ??

Cheers ! Paul


Mon Sep 19, 2016 10:15 pm
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Post Re: 40m 2 ele wire antenna
You haven't a hope in hell of keeping a 40m multi-element loaded yagi in the air using 6 fishing poles.
The 15m you have is enough width for the elements after you shorten them using coils but the extra weight those 2 coils will add to each element will be too much for the fishing poles......more of the elements will be touching the ground than in the air.

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Mon Sep 19, 2016 11:21 pm
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 40m 2 ele wire antenna 
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Good point....I wonder how critical that is providing the other element(s) follow with the same concave shape :)

might need to learn about eznec and see if it could be modelled....otherwise trial and error with analyzer!

Cheers 73 Paul


Tue Sep 20, 2016 11:24 am
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Post Re: 40m 2 ele wire antenna
PaulGB wrote:
Good point....I wonder how critical that is providing the other element(s) follow with the same concave shape :)

might need to learn about eznec and see if it could be modelled....otherwise trial and error with analyzer!

Cheers 73 Paul


Also, it would help if you said what your reason for wanting a Yagi is.

Do you want to:
a) Work more DX on 40m, or
b) Make your Inter-G / Near Europe signal stronger.

They are very different antennas.

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Tue Sep 20, 2016 12:16 pm
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Post Re: 40m 2 ele wire antenna
If you are looking for an inter-G ''cloudwarmer', then, by happy coincidence, Mr Pythagoras says that your roof is 21m across on the diagonal.

So it would be a doddle to lay your 'ground reflector' across that, with an Irish Inverted 'V' strung between non-conductive poles above it.

That's for NVIS of course, it would be crap for DX.

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Tue Sep 20, 2016 1:20 pm
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 40m 2 ele wire antenna 
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Post Re: 40m 2 ele wire antenna
Quote:
Also, it would help if you said what your reason for wanting a Yagi is.

Do you want to:
a) Work more DX on 40m, or
b) Make your Inter-G / Near Europe signal stronger.

They are very different antennas


To work DX in Asia/Pacific area. It would be pointing NE by my reckoning so a fixed 2ele Yagi should work well here.

Thanks for the info on NVIS Ant.

73 - P


Wed Sep 21, 2016 8:35 am
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Post Re: 40m 2 ele wire antenna
PaulGB wrote:
Quote:
Also, it would help if you said what your reason for wanting a Yagi is.

Do you want to:
a) Work more DX on 40m, or
b) Make your Inter-G / Near Europe signal stronger.

They are very different antennas


To work DX in Asia/Pacific area. It would be pointing NE by my reckoning so a fixed 2ele Yagi should work well here.

Thanks for the info on NVIS Ant.

73 - P


Splendid. I'm yer man for ''Anti-DX'' antennas :)

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Wed Sep 21, 2016 8:45 am
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Post Re: 40m 2 ele wire antenna
If you didn't want the Moxon layout you could fold the two full size wire elements into a couple of Ms like the hex beam does, again pretty well 50 ohms at the feed point so just a 1:1 current balun between the coax and driven element.

Might lend itself better to aiming in a favoured direction on that square of roof?

Cheers, Dave.


Wed Sep 21, 2016 6:43 pm
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Post Re: 40m 2 ele wire antenna
Given the 15m x 15m overall size, a dipole driven element could be stretched diagonally corner to corner and a reflector and director then returned around the two opposite corners "Spiderbeam" fashion.
You couldn't support it using 4 fishing poles though, you'd need to install something more robust.


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Wed Sep 21, 2016 7:36 pm
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