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Author Topic: wiring a UNUN  (Read 395 times)
N4GRN
Member

Posts: 47




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« on: January 09, 2003, 01:05:07 AM »

Can someone explain how I wire a UNUN at the feed point of my screwdriver antenna.

I have a toroidal core with 5 turns of #18 wire (a twisted pair) wound around the core. My question is does one end of wire "a" go to antenna feed, one end of wire "b" go to ground, then what do I do with the other ends of wire a & b? My feeling is that the other ends of a&b get shorted as that makes the most sense to me.

Some schematics show shorted and some open. The antenna mfg drawing shows one end at the coax feed/antenna feed point and the other end at ground/coax shield but does not show how to treat the other ends of each wire.

I am confused. Any help will be appreciated and maybe a short explanation of why?

73 N4GRN
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N6QL
Member

Posts: 30


WWW

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« Reply #1 on: January 09, 2003, 01:41:33 AM »

Why don't you call the antenna manufacturer and ask them?

If it is truly an UNUN that you want I can only think of one configuration:

......+----------^^^^^^^^^^^---------O
.......|
O----|
.......|
......+------------------------------+
.......................................|
.......................................|
.......................................|
.......+------^^^^^^^^^^^^--------+
.......|
....._+_
...../ / /

Ignore the dots - it's the only way I could get things to line up because the forum strips out leading spaces

This is a 12.5 ohm to 50 ohm Ruthroff UNUN which is recommended to be wound on a rod core by Jerry Sevick.

The other configuration that Jerry shows is (again, ignore the dots):

O------------^^^^^^^^^^^^^^^---------O


.....+-------^^^^^^^^^^^^^^^---------O
......|
..._+_
.../ / /

This is a 50 ohm coax to 50 ohm balanced - a BALUN.

Hope this helps...

Ron Curry
N6QL  
       
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WA4PTZ
Member

Posts: 528




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« Reply #2 on: January 09, 2003, 05:30:39 AM »

I don't know what kind of screwdriver antenna you have
or if it varies from mine, but figure one of N6QL's
reply is how mine is done and it works great.
73 - Tim
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K0BG
Member

Posts: 9863


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« Reply #3 on: January 09, 2003, 09:57:02 AM »

George, in about a week or two, my article about using UNUNs for matching mobiles antennas will get posted. It has a schematic and instructions. If you'll e-mail me, I'll send it to you.

Alan, KØBG
k0bg@aol.com
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AC5UP
Member

Posts: 3864




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« Reply #4 on: January 09, 2003, 04:06:26 PM »

If I recall my readings from Jerry Sevick (K2FMI) correctly, a Guanella choke balun (the second figure above, a bifilar winding with one wire designated as 'Hot' and the other 'Ground') will work as both a Balun and UnUn.

The application is essentially a line isolator / common mode 'breaker' decoupling the outer coax braid. If you're using RG-8X for the feed you can wrap 8 turns or so on a T-240, Mix 61 or 43, toroid and achieve the same goal. Otherwise, if you're running 100 watts or so, figure 8 turns of #18 insulated wire on an appropriately sized core of Mix 61 or Mix 43 material. Using enameled wire will give a winding impedance lower than optimum. If you can find some wire with a thin layer of Teflon insulation, that will get you closer to 50 ohms...

- AC5UP
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