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Author Topic: Is this a high Q loading coil?  (Read 1052 times)
JAHAM2BE
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« on: April 22, 2013, 10:10:57 PM »

In this image you can see a hand-wound air-core coil on the right (on the left is a reference AirDux inductor): http://blog-imgs-54-origin.fc2.com/t/a/k/take103/201211241704430c4s.jpg

In the original source (in Japanese), you can see the winding procedure: http://take103.blog.fc2.com/blog-entry-70.html . The idea is to wind the coil on a form wrapped in plastic wrap. Then, some sort of glue is used to hold the turns in place. Finally the inner coil form and the plastic wrap are removed. As you can see, the result has some unevenness in spacing and height, and also shows some twist that is introduced after removing it from the form.

I'm thinking of using a similar technique to make a larger coil for loading a short dipole. I'll adjust the coil dimensions so that the required inductance can be achieved in a "square" coil form factor (not too long and skinny, and also not too short and fat).

Do you think the pictured coil construction technique would be able to achieve a coil Q of 500 or more at 7 MHz, using 2mm-diameter copper wire?

I'm aware of another technique of using plastic grommet strips (http://www.eham.net/articles/23124), but I can't seem to find a supplier for those grommet strips locally, so I need to find another method, like the above method using glue.
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K3VAT
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« Reply #1 on: April 23, 2013, 05:01:53 AM »

...

Do you think the pictured coil construction technique would be able to achieve a coil Q of 500 or more at 7 MHz, using 2mm-diameter copper wire?

...

Possibly, W8JI measured coil Q of a number of various coils including a #12 miniductor (close to 2mm wire) and found that the peak Q between 300 and 500 and the Q at 80% resonant frequency between 200 and 400.  The page:
http://w8ji.com/loading_inductors.htm contains other valuable notes that one needs to be fully familiar with to properly design loading coils.  If you haven't checked it out, it is a must read for coil builders.  Let us know how your project is going?  GL, 73, Rich, K3VAT
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K3VAT
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« Reply #2 on: April 23, 2013, 06:11:02 AM »

...
I'm thinking of using a similar technique to make a larger coil for loading a short dipole.
...

So how short is the 'short dipole'.  Do you intend to use wire, simply hung between two high supports or something more sophisticated such as using Al tubing and/or making it rotatable?  End loading with capacitive hats are a very viable option as the losses experienced as opposed to a loading coil, are less.  Plus, the feed point Z is often higher, facilitating easier Z matching.  GL, Rich, K3VAT
 
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JAHAM2BE
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« Reply #3 on: April 23, 2013, 09:08:08 AM »

So how short is the 'short dipole'.  Do you intend to use wire, simply hung between two high supports or something more sophisticated such as using Al tubing and/or making it rotatable?

2 meters. You can read about the details of the design in the other thread here: http://www.eham.net/ehamforum/smf/index.php/topic,89392.0.html

Here's a photo of how it looks so far. I've got the mechanical issues sorted out. Now I just need to add the loading coils, the capacity hats, and the shunt coil at the feedpoint for matching. Plus probably a balun.

http://www.freeimagehosting.net/newuploads/11ec3.jpg

Thanks for the W8JI link about loading coils. Definitely worth studying.
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K3VAT
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« Reply #4 on: April 23, 2013, 11:09:40 AM »

...

Here's a photo of how it looks so far. I've got the mechanical issues sorted out. Now I just need to add the loading coils, the capacity hats, and the shunt coil at the feedpoint for matching. Plus probably a balun.
http://www.freeimagehosting.net/newuploads/11ec3.jpg

Ah, a vertical dipole - nice construction.  You seem to have identified all the necessary components (loading coil and cap hat, one for each side; and shunt coil at the feedpoint.  Thanks for sharing.  73, Rich, K3VAT
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