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 Post subject: 80m Loop Antenna Calculator
PostPosted: Jan Mon 08, 2018 8:55 am 
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Joined: Aug Sat 13, 2016 6:03 am
Posts: 100
I'm thinking about building an 80m receive only loop antenna. What have you found to be the most accurate calculator on line? I have found four, and none will give me identical calculated values. Seems as though each has been designed for a specific antenna shape. I'm thinking about a two turn circular loop and haven't yet decided on the material. It doesn't appear to make much difference for reception besides the nulling factor. From what I've read on line, this does not seem to be a very definitive subject. Most builders have a "let's try it and see" approach. I'd rather learn by others failures. Thanks in advance for any help locating a somewhat accurate calculator.


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Jan Tue 09, 2018 3:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 442
Location: Missoula, MT
Since you mentioned a two-turn circular loop I am presuming you are interested in a so-called "magnetic loop". I am not aware of any online calculators but the prevailing wisdom on these seems to center on the idea that the total wire length in the loop should be .085 wavelengths at the highest frequency of interest.

Since the top of the 80m band is 4 MHz, you have 637 cm (251 inches) of wire (or tubing).

Since the perimeter of a circle is 2*pi*R, this is a loop diameter of 80 inches.

A 2-turn loop would be half of that at 40 inches diameter.

You might check out the N6RK webpage for ideas on how to couple and feed the loop.
http://www.n6rk.com/loopantennas/pacificon.pdf


- Steve


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Jan Tue 09, 2018 4:38 am 
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Joined: Aug Sat 13, 2016 6:03 am
Posts: 100
Thanks Steve. This is only one of many web pages I have spent countless hours reading. Technically the term "magnetic loop" refers to the inductive coupling between the little loop which connects to your station. For receiving only, this loop is an optional feature. I plan to take the signal off the loop ends that have a tuning capacitor across them. I will probably fabricate an inductive loop later, just to see the difference. Right now I need to find an accurate calculator.


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Jan Tue 09, 2018 5:18 am 
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Joined: Apr Thu 12, 2007 3:24 am
Posts: 1343
Location: Milwaukee,WI
How far apart are the various calculators ( for the same shape ) that you don't feel safe to use an average of the different results?

Or haven't you settled on a particular shape yet?


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Jan Tue 09, 2018 9:22 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2154
Location: Saskatoon
What exactly are you trying to calculate? Inductance, optimum diameter, or something else?


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Jan Wed 10, 2018 7:28 am 
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Joined: Aug Sat 13, 2016 6:03 am
Posts: 100
I have found a variation of over 200pf in the suggested values for the tuning capacitor. The answer, is no doubt, in there somewhere but it would be nice to narrow it down a little closer. You would think I could find a calculator for a circular receiving loop. Not yet.


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 Post subject: 80m Loop Antenna Calculator
PostPosted: Feb Tue 06, 2018 5:10 pm 
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Joined: Jan Sun 28, 2018 1:52 pm
Posts: 5
Location: Finland
i am hopeing to build a magnetic loop antenna can anyone please help as to what type /size of tuning capacitor i will need to cover as many of the ham bands as possable ???


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 Post subject: Re: 80m Loop Antenna Calculator
PostPosted: Feb Wed 07, 2018 9:32 am 
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Joined: Aug Sat 13, 2016 6:03 am
Posts: 100
Will this be a receiving only loop or are you going to use it with your transmitter also? How many watts? When I started researching this subject I must have spent 40 hours reading every post on the internet that had anything to do with loop antennas. There is just an overwhelming amount of material to wade through and there seems to be no definitive answers. What I did learn ....for the best results the one loop size fits all is not a reality, although some people have tried. I think a 160m and 80m loop would be one size and 10m, 20m and 40m might be the second size. Two adjacent bands seem to work well together with one size loop. If you plan to have a "tuned loop" that would cover say from 80m to 20m I would guess the total capacitance would be 750 t0 1000pf. Now if you're doing 160m and 80 m you could probably get by with around 5oopf. in the 20m range I'm guessing around 200pf. I made a list of what everyone had done on every article I read. When I finished I had values from180pf to 1000pf. That's why I asked about a good online calculator here.

My receiving antenna is for mainly 80m and a little 40m. I found a capacitor with 3 gangs (400pf each) out of an old radio. I plan to experiment with it by jumping the gangs together one at a time till I find resonance in my loop. I plan to connect my loop to my receiver and tune 4mc. Then I will set my signal generator to 4mc. I should hear something in my receiver. Then I'll tune my capacitor on the loop for the strongest signal and measure the capacitance. If I do this for all the frequencies I want I can get a pretty close idea of what capacitor to use permanently.

In the end I want to tune from 3.5mc to 6.5mc and hopefully I can use a smaller capacitor like 100pf if I connect a fixed capacitor in parallel with it. The ideal situation is to use a dual gang capacitor and connect the loop to the stator terminals. This will give you a higher "Q" when you do not use the frame and the wipers and the ball bearings to carry the signal. Just remember, you'll will be working with roughly half the total capacitance. Try to copy the good points of what others have done. There has been a lot of development by people who have spent countless hours designing these. Don't try to reinvent the wheel.

Keep in mind that you will no doubt need an RF amplifier mounted at your loop to boost the signal to your receiver. I'm working on that now. There's no way this can be in the circuit if you are transmitting. Last question. Is this going to be indoors or out or both? Good luck sorting all this information out. I hope for both our sakes it's going to be worth the effort.


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