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 Horizontal Mag Loop 
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Post Horizontal Mag Loop
Good Afternoon

I am planning to work on 40M when I get up to speed on CW and get a tranciever.

Anyway i am planning on building pretty much everything and am currently planning the antenna. I think I will have to go down the Mag Loop road as space is at a premium.

The question I have is I quite often see them in a horizontal position, this may be best from a Station Manager point of view, but will it impact the performance a great deal?

I was thinking of building something like this

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10223

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Mon Feb 06, 2012 4:47 pm
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 Horizontal Mag Loop 
Silent Key

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Post Re: Horizontal Mag Loop
From AA5TB's web site:

Quote:
The main difference between mounting a small loop vertically or horizontally is the polarization and the orientation of the antenna's pattern null. E-field losses would conceivably be greater for a horizontal loop that is close to the ground. Some literature I've read suggest that the pattern for a horizontally mounted small loop will have a lower take off angle then other horizontal antennas. I've seen no justification for this claim except that there will always be a null straight up (broadside) due to the nature of a small loop antenna's free space pattern and this will cause there appearance of a lower angle of radiation compared to a low dipole that has the main lobe straight up. This can be viewed like a low dipole elevation pattern (a wide lobe straight up) with a notch taken out at the zenith (90 degrees). However, when the far fields are compared at a lower angle, such as 10 degrees, the results are more comparable


Of course, having the loop horizontal and the sharp null overhead makes it less useful for nulling interference.

Note that the loop design in the link you gave is for QRP operation only - the limiting feature is the voltage breakdown of the capacitors.

73,
Steve G3TXQ


Mon Feb 06, 2012 4:59 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
Hand't factored in the nulls I suppose I will have to see when i put it up.

As for it only being QRP that is no problem I will only have QRP rigs to use.

Thank You

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Mon Feb 06, 2012 5:23 pm
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 Horizontal Mag Loop 
Silent Key

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Post Re: Horizontal Mag Loop
Do try to minimise losses!

The design in that link uses very thin wire, which dissipates a lot of the applied power - the calculated efficiency comes out at about 2% on 40m; that's 100mW radiated for 5W applied! If you could use a 1/4" conductor instead of 24AWG, the efficiency would be much better at 15%.

73,
Steve G3TXQ


Mon Feb 06, 2012 5:40 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
I made and used that design but slightly different , i used just 1 polyvaricon cap with a little 40 odd pf cap i could switch in and out .. it didn't need this much on the switched cap i don't think if i can remember but was the first i pulled from the junk box..

i worked EU from the front garden at ground level and was quite surprised at how well it performed. i made mine with the usual speaker wire i use for allsorts..

below is a pic of the cap boxed up .. can't find the bottom box which holds the ferrite core and bnc


Attachments:
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ggg 020.jpg [ 26.84 KiB | Viewed 2960 times ]

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Mon Feb 06, 2012 6:13 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
Learning all the time! I guess the portability of that design has its downsides.

I have seen some designs using coax too, is it a case of the thicker the better or is there a formula that I can apply?

Would something like copper pipe be suitable?

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Mon Feb 06, 2012 8:02 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
There are better designs out there but it all depends how much effort you want to put into one ..

i'm looking at building one with a 1m diam copper loop or maybe a hoola hoop with wire inside and a decent air spaced cap .. ( get em off e bay quite cheap )

Look up on you tube , there is a VK station ( not sure of call or user name off my head) who likes messing with simple loops and seems to do ok with them for the effort put into them ..


the above design is a nice fun design . i enjoyed just messing around with it for a while even though i knew it wasn't the best of designs.. was just nice to do it for the sake of it ..

billy

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Mon Feb 06, 2012 8:15 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
I have seen that guy in VK who does the pedestrian mobile videos, he seems to get reasonable reports on ssb phone so I am sure with CW he would be doing great.

A lot of the designs I see have very poor descriptions and leave a lot to guess work. It would nice to be able to build something like the MFJ one.

I have a spare decent spaced cap sat in the junk box at the moment, so that would probably go in anything that involved some work.

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Mon Feb 06, 2012 8:54 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
http://www.g4tph.com/

here is a guy selling them at a reasonable price .. not the best but ok i suppose ..

he had a write up in radcom and explained how he built it , very simple if i remember , maybe have a look there and get an idea..


billy

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Mon Feb 06, 2012 9:00 pm
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 Horizontal Mag Loop 
Silent Key

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Post Re: Horizontal Mag Loop
A 16ft perimeter loop like the one in the link will have a radiation resistance of around 0.03Ω on 40m. That means any loss resistance has to be kept very small if the loop is to be reasonably efficient.

The places where loss resistance usually "creeps in" are:

* The wire conductor loss. The larger the wire diameter, the less the conductor loss; that's why you see some professional loops made of 2" diameter copper pipe. Using coax braid would be much better than 24AWG wire, although the braid would not be as effective as the same diameter copper pipe.

* Connections to the moving vanes of the variable capacitor; that can be avoided by using a "split stator" capacitor where no connection to the moving vanes is actually needed.

* Connections between the loop and the fixed vanes of the capacitor.

73,
Steve G3TXQ


Mon Feb 06, 2012 9:20 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
i made the one in the top link just for fun to rx really , it worked really well as an rx antenna and the nulls were impressive . i tx'd just because i was set up and made a couple of contacts on 40 .. DL and F if not mistaken ..

spoke to quite a few ops inter G using the mfj loops with them sat on tables etc in the living rooms with nice sigs.

i'll get round to making a half decent one after i finish fixing this CP6 :banghead:

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Mon Feb 06, 2012 9:33 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
Thanks Steve and Billy

At least i know I can make something workable, it will just take some experimeting.

Jon

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Mon Feb 06, 2012 9:47 pm
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 Horizontal Mag Loop 
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Post Re: Horizontal Mag Loop
Sorry one more question.

Would thisbe reasonably suitable?

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Tue Feb 07, 2012 10:05 am
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 Horizontal Mag Loop 
Silent Key

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Post Re: Horizontal Mag Loop
M6BYR wrote:
Sorry one more question.

Would thisbe reasonably suitable?

I don't see enough technical detail there to make a judgement. Could you not simply use a length of RG58, or better still RG213?

73,
Steve G3TXQ


Tue Feb 07, 2012 10:45 am
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