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Author Topic: A Magnetic Loop for 6m.  (Read 3017 times)
GILGSN
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Posts: 208




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« on: January 03, 2013, 03:18:10 PM »

Building a 1.4ft. diameter loop for 6m:

http://radiopreppers.com/index.php/topic,325.0.html

Gil.
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WX7G
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« Reply #1 on: January 05, 2013, 08:47:24 AM »

Gil, that is very nice! I like the the feed with the torroid.
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GILGSN
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Posts: 208




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« Reply #2 on: January 06, 2013, 04:14:57 PM »

Thanks. I should have made it a little smaller, for a little more capacitance. Also, I still need to experiment with different number of turns on the toroid...

Gil.
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W8NSI
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« Reply #3 on: January 06, 2013, 07:50:26 PM »

Another possibility to experiment with: because you are using a toroid for coupling, try moving the gap with the capacitor down next to the toroid. Since the high voltage point of the loop is opposite side this should eliminate need for high voltage capacitor.
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73 de w8nsi/nnn0uzw jim
GILGSN
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Posts: 208




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« Reply #4 on: January 06, 2013, 08:05:06 PM »

Thanks. I didn't know you could do that, but indeed, why not?!
Would that affect anything else?

Gil.
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WB6BYU
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« Reply #5 on: January 06, 2013, 08:15:35 PM »

Quote from: W8NSI
...try moving the gap with the capacitor down next to the toroid. Since the high voltage point of the loop is opposite side this should eliminate need for high voltage capacitor.


The high voltage point is ALWAYS across the capacitor.  Where else could it be?  Everywhere
is a continuous conductor and doesn't have a voltage drop.

Moving the toroid closer to the capacitor will change the impedance match, but
won't change the voltage across the variable capacitor unless you make the loop
more lossy.
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KQ6Q
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« Reply #6 on: January 06, 2013, 09:02:29 PM »

Why a magnetic loop for 6m? practice with the technique ? a Squalo type antenna has a simple dipole feed impedance, much less complicated to make, and a very reasonable size....
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GILGSN
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Posts: 208




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« Reply #7 on: January 06, 2013, 10:11:40 PM »

Quote
Why a magnetic loop for 6m? practice with the technique ? a Squalo type antenna has a simple dipole feed impedance, much less complicated to make, and a very reasonable size....

Well, sometimes you just have to do things the hard way...  Wink

Experimenting, yes...

I don't know what the radiation pattern of a squalo is, but the loop radiates at all angles...

Gil.
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KU3X
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Posts: 145




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« Reply #8 on: January 08, 2013, 10:54:34 AM »

Gil,
Nice mechanical layout for your 6 meter loop. The very first one I made I used the same matching that you did. I was not happy with the results. I got it to work but each band gave different results. I changed to a smaller loop inside of the main loop. The smaller loop was 1/5 the size of the big loop. I used plastic ties to hold the smaller loop on the mast. I was able to slide that loop up and down until I got the best match per band. I also used a fiberglass driveway marker going from the bottom of the loop to the tuning cap. My loop is designed to work 12 to 40 meters.
I found the magnetic loop to be the best table top antenna I have even used.
Take a look at what I built and maybe it will give you some ideas.

http://www.ku3x.net/portable-qrp

After seeing your 6 meter loop, I may build one to cover 6 and 10 meters. I'd like to be able to cover all bands from 6 to 40 meters and building one more will do the job.
Good luck with your project. Well done.
Barry KU3X
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GILGSN
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Posts: 208




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« Reply #9 on: January 08, 2013, 11:07:56 AM »

Interesting Barry, thanks. I might try that for the next one...
What's in the box where the coax goes, a choke?

Gil.
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KU3X
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Posts: 145




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« Reply #10 on: January 08, 2013, 12:33:49 PM »

That's correct. It is a line isolator. Your antenna will need a choke or line isolator. For your antenna,  just get some 61 ferrite material and wrap a few turns around the core and get some slip on beads.

The most power I run on any of my loops is 20 watts. I had a bigger tuning cap and I could run up to 100 watts, but I could not get a low enough value to go above 20 meters. I did not want to use a vac vari so I  used a small dual section air cap, wired it in series to increase the voltage breakdown value and get a lower capacitance so I could get on 12 meters.
Remember, 20 watts is only a tad over 1 S unit down from 100 watts. You save on battery current drain, you are exposed to less of an RF field and you can use a smaller cap, meaning you  don't need a vac vari.

Barry
www.ku3x.net

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