Delta loop home made

Joined: 8:01 AM - May 02, 2016

10:20 PM - Jul 11, 2017 #1

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
Last edited by TimH1971 on 10:38 PM - Jul 11, 2017, edited 2 times in total.
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Joined: 4:23 PM - Dec 27, 2010

10:58 PM - Jul 11, 2017 #2

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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Joined: 8:01 AM - May 02, 2016

5:39 AM - Jul 12, 2017 #3

Meissen wrote: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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Joined: 3:05 PM - May 11, 2012

7:21 AM - Jul 12, 2017 #4

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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Joined: 8:01 AM - May 02, 2016

8:20 AM - Jul 12, 2017 #5

Rotel RVC 240 wrote: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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Joined: 5:20 PM - Jun 21, 2017

8:35 AM - Jul 12, 2017 #6

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.


antenna_mag_loop_coupling_ferrite.jpg
Last edited by Walruss on 8:54 AM - Jul 12, 2017, edited 2 times in total.
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Joined: 8:01 AM - May 02, 2016

10:40 AM - Jul 12, 2017 #7

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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Joined: 5:20 PM - Jun 21, 2017

11:13 AM - Jul 12, 2017 #8

TimH1971 wrote: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.
quad_loop_impedance_and_gain_chart.jpg
quad_loop_impedance_matching_with_balun.jpg
Last edited by Walruss on 11:14 AM - Jul 12, 2017, edited 1 time in total.
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Joined: 8:01 AM - May 02, 2016

11:27 AM - Jul 12, 2017 #9

Walruss wrote:
TimH1971 wrote: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 50Ù impedance of feeder to the 100Ù or so of the loop.
Thanks Chris.

Tim.
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Joined: 5:20 PM - Jun 21, 2017

12:09 PM - Jul 12, 2017 #10

TimH1971 wrote:
Walruss wrote:
TimH1971 wrote: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 50Ù impedance of feeder to the 100Ù 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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