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Delta loop home made
Topic Started: Tuesday, 11. July 2017, 22:20 (690 Views)
TimH1971
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26 Charlie Tango 2116

Anyone tried making or using one of these for 11m?

I'm looking to make a rectangular shaped one with the feed point at the centre of the base.

Question is that I know it needs 75ohm coax such as rg59 for a quarter wavelength to help impedence and then attach this to the rg58 I will use to connect to the radio.

But.... can pl259 plugs designed for rg58 also fit rg59 coax?


Tim
Edited by TimH1971, Tuesday, 11. July 2017, 22:38.
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Meissen
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Hi Tim
58 and 59 are both 4.9ml, so yes is the answer. Good luck with the project.
474 jon
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TimH1971
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26 Charlie Tango 2116

Meissen
Tuesday, 11. July 2017, 22:58
Hi Tim
58 and 59 are both 4.9ml, so yes is the answer. Good luck with the project.
474 jon
Thanks for the reply. Much appreciated.
73s
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Rotel RVC 240
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26 Charlie Tango 950

I used 75 ohm tv cable approx 2.2m and the loop worked well but not as good as the Moxon. Andy591/p will tell you everything you need to know. Look here http://charlietango.co.uk/topic/9030989/1/#new
26 CT 950 YOUR SIGNAL IS ONLY AS GOOD AS YOUR ANTENNA AND THE PROPAGATION https://www.facebook.com/DRX111/
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TimH1971
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26 Charlie Tango 2116

Rotel RVC 240
Wednesday, 12. July 2017, 07:21
I used 75 ohm tv cable approx 2.2m and the loop worked well but not as good as the Moxon. Andy591/p will tell you everything you need to know. Look here http://charlietango.co.uk/topic/9030989/1/#new
Thanks Paul
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Walruss
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Good morning, Tim! :)

You may find this magnetic loop calculator interesting. http://www.iw5edi.com/software/magnetic-loop-calculator

There is a download link to a compressed file - loopcalc.exe - near the bottom of the page.

You can't connect a feedline directly to these loop antennas. There are three ways of doing the coupling:

1.) By means of a small coupling loop roughly 1/6th the diameter of the main loop.

2.) By means of a DIY ferrite transformer

3.) By means of a gamma match. (I don't like this one - hard to find the optimum position - but other folk seem to get on with it.)


I have found the ferrite transformer easy to implement using 10mm copper plumbing pipe. You just wrap 50Ω worth of hookup wire - I used PTFE but not essential - around the ferrite toroid and slide it onto the copper pipe. See attached below. The Q is astonishing so tuning is extremely sharp.


Attached to this post:
Attachments: antenna_mag_loop_coupling_ferrite.jpg (38.2 KB)
Edited by Walruss, Wednesday, 12. July 2017, 08:54.
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TimH1971
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26 Charlie Tango 2116

Re: Quad Loops - any idea how quiet these are? QRM is the thing I am trying to lessen above all else.

Appreciate the help so far guys.

Tim
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Walruss
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TimH1971
Wednesday, 12. July 2017, 10:40
Re: Quad Loops - any idea how quiet these are? QRM is the thing I am trying to lessen above all else.

Appreciate the help so far guys.

Tim



A balanced loop gives some immunity to local common mode interference - i.e. the equal and opposite currents induced in both arms cancel eachother out.

Note below attached the low gain of the square quad loop, and the gains and impedances of the various loop permutations.

Also below attached, design of a simple ferrite balun to balance loop and match 50Ω impedance of feeder to the 100Ω or so of the loop.
Attached to this post:
Attachments: quad_loop_impedance_matching_with_balun.jpg (50.05 KB)
Attachments: quad_loop_impedance_and_gain_chart.jpg (90.54 KB)
Edited by Walruss, Wednesday, 12. July 2017, 11:14.
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TimH1971
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26 Charlie Tango 2116

Walruss
Wednesday, 12. July 2017, 11:13
TimH1971
Wednesday, 12. July 2017, 10:40
Re: Quad Loops - any idea how quiet these are? QRM is the thing I am trying to lessen above all else.

Appreciate the help so far guys.

Tim



A balanced loop gives some immunity to local common mode interference - i.e. the equal and opposite currents induced in both arms cancel eachother out.

Note below attached the low gain of the square quad loop, and the gains and impedances of the various loop permutations.

Also below attached, design of a simple ferrite balun to balance loop and match 50 impedance of feeder to the 100 or so of the loop.
Thanks Chris.

Tim.
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Walruss
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TimH1971
Wednesday, 12. July 2017, 11:27
Walruss
Wednesday, 12. July 2017, 11:13
TimH1971
Wednesday, 12. July 2017, 10:40
Re: Quad Loops - any idea how quiet these are? QRM is the thing I am trying to lessen above all else.

Appreciate the help so far guys.

Tim



A balanced loop gives some immunity to local common mode interference - i.e. the equal and opposite currents induced in both arms cancel eachother out.

Note below attached the low gain of the square quad loop, and the gains and impedances of the various loop permutations.

Also below attached, design of a simple ferrite balun to balance loop and match 50 impedance of feeder to the 100 or so of the loop.
Thanks Chris.

Tim.
At 27.350 MHz one wavelength is 10.96m.

We must allow for the velocity factor also called velocity of propagation of the wire, which is a nominal 0.95 for a straight copper wire. (much less for some coaxial cables!) This is the speed that an electromagnetic wave travels down the wire compared with the speed of an electromagnetic wave in a vacuum. So slower down the wire.

10.96m times 0.95 is 10.41m. (10.88*0.95 = 10.41)

This 10.41m we would call the electrical length of a wave of frequency 27.35MHz

Each of the four sides of a fullwave square quad loop would therefore be 10.41 divided by 4,
which is 2.6m.

A circular fullwave loop cut for 27.35 MHz and therefore having an electrical length of 10.41m will have a diameter of 3.31m - quite a big circle to keep in shape I'd say.
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Kaos
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13 Charlie Tango 013

Here is my 2 element homebrew loop.

Posted Image

Pictured below is my BALUN. 75 ohm sat coax. I have long forgotten the length of it but found that the coke bottle was the best size for the 10 or so turns round the bottle.

Posted Image

Performance wise is kicks my 2 ele moxon loop into next week. Its VERY directional and the QRM FOR ME is very nearly nulled. I don't have much anyways but its a (slight) improvment.
13CT013 Tim aus Germany

So Mote it be
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Walruss
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You're lucky to have so much space! :wave:
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