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Author Topic: RF Decoupling on coax  (Read 281 times)
N9NEO
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Posts: 93




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« on: December 28, 2002, 07:21:35 AM »

I am about to erect a 5BTV verticle.  The instructions say to wind 10 turns of coax around a 6" form at both antenna end and transmitter end.  Unfortunatly I don't have enough coax.

I have access to some 4" high permiability toroids used for emi filters.  Can I wind 2-3 turns on one of these to get same effect?

regards,
Bob
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K0BG
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« Reply #1 on: December 28, 2002, 08:14:14 AM »

Maybe if they are the right material mix. If you don't know, don't use them. The cheapest solution is more coax and a coupler or two.

Alan, KØBG
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WA4PTZ
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Posts: 528




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« Reply #2 on: December 28, 2002, 08:18:06 AM »

Yes, You can. 3 turns should work, but a few more
would be better . Be careful not to bend the coax
too tightly and secure the turns with tape or cable
ties. You may be able to find a java script or a
freeware to calculate the turns.
73 - Tim
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AC5UP
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Posts: 3891




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« Reply #3 on: December 28, 2002, 01:46:11 PM »

The cores from an EMI filter are likely powdered iron with a high permeability factor as they were chosen with a 60 Hz environment in mind.

This doesn't mean you can't use them, as your intended application will be like running the coax through a high-permeability RF Sponge with the goal of attenuating RF running outside the coax shield. If you can lay hands on the cores at low or no cost, go for it... Those 4" jobbies don't come cheap or easy!

I've done the same with EMI cores in the 2" range on RG-8X without a problem, just avoid coiling the coax too tight. Loose enough is good enough as you don't need to nail the last microwatt on the sheath and the recommended air coil isn't 100% effective, either...

- AC5UP
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N6AJR
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Posts: 9910




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« Reply #4 on: December 28, 2002, 03:56:16 PM »

I have been using mine with a 3 turn coil at the antenna and none at the rig, (same problem short cable) and it works fine  I run mine through a tuner.  I have it ground mounted with no radials and I hav worked all states and all continents an lots of great dx. I had radial but they didn 't change any thing so I pulled them up.  tye off 3 pieces of nylon 1/4 inch rope up above the big star ring at about 20 feet as guys, and this will keep the swaying down in the wind. I have used mine for 2 years now and I love it.  It is a great antenna, and puts out a good signal, listen to me any nite on 40 meters at the HHH net and you will hear me well...  73  tom N6AJR
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N9NEO
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Posts: 93




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« Reply #5 on: December 28, 2002, 07:50:35 PM »

Thanks for the info.  The cores are a Hi-perm ferrite.  They're used on 3 phase inverters for motor controls to reduce emi back on the power line.  They're wound in a common mode configuration so the 60hz (x6) components cancel, otherwise they  would saturate.

73s
Bob
 
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