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Author Topic: Ferrite Beads for coax current chokes #Type/Amount?  (Read 3211 times)
K1WJ
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Posts: 458




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« on: April 12, 2012, 10:54:14 AM »

Coax is Andrew 240 - RG8X size - 240 lower loss on HF & otherwise than 8X.

Antenna is ground mounted adjustable whip for 6m to 20m with 16 ground radials.

Instead of making coax ugly balun - I would like to use snap-on ferrite beads to current choke.

What ferrite material #31 or #43 or #73. #31 is for wider freq. range? #73 can cause coax to burn/melt? #43 for 25mhz to 300mhz?

Is #31 good for 6-20m? #43 better?

Next, is how many to use just prior to antenna feedpoint? 6? 8?

Best place to obtain these ferrite snap-ons?

Any definitive answers? Thanks & 73 K1WJ David
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WX7G
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« Reply #1 on: April 12, 2012, 10:59:02 AM »

Type 31 would be best. The DX Engineering DXE-CSB-275B snap-on chokes are type 31 and will fit your RG-8X size coax. They are 10 for $23.25.

At 14 MHz this ferrite exhibits an impedance of 120 ohms. Use all 10 and you have a 1200 ohm choke.

Link to the datasheet: http://www.dxengineering.com/TechArticles.asp?ID={54C2338D-3ED0-48C3-946F-F343A5C7555D}

« Last Edit: April 12, 2012, 11:12:55 AM by WX7G » Logged
W0BTU
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« Reply #2 on: April 12, 2012, 12:08:53 PM »

Type 31 ferrite is "magic" stuff, indeed. :-)  Of course, you have to wind it correctly; check out K9YC's relevant PDFs at http://audiosystemsgroup.com/publish.htm.

You can buy Fair-rite 31 material 2.4" OD cores for seven bucks each from Mouser (which is what I use.) Maybe the DXE is a better deal.
« Last Edit: April 12, 2012, 12:11:35 PM by W0BTU » Logged

K1WJ
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« Reply #3 on: April 12, 2012, 03:31:34 PM »

Thanks for the links for info.

Is a 1000 ohm current choke the minimum to shoot for, 6m-20m range in operating freq?

73 K1WJ David
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W0BTU
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« Reply #4 on: April 13, 2012, 02:39:09 PM »

If your only interest is 20 - 6 meters, there may possibly be a better choice that #31.

31 material was developed as a 'lower frequency enhancement' to #43, and it works better at 80 and 160 than #43.

As I suggested above, take the time to read K9YC's excellent info.

I'm not saying that #31 won't work. Just study before you buy or build. :-)
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WX7G
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« Reply #5 on: April 14, 2012, 07:36:29 AM »

I have a similar antenna and use no balun. Try it.


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KM1H
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« Reply #6 on: April 14, 2012, 11:47:08 AM »

I doubt you will ever find DXE to be a "better" deal on anything. They charge you extra to give you bragging rights Roll Eyes

Id shop Mouser and Amidon first and then go for the best deal.
OTOH The Fair-Rite 2643540002 at Mouser is all of $0.63 each. It is a 43 material which will be better at your frequencies but they also have a identiical dimension 31 material at $1.02 a pop.

The 2.4" diameter 31 mix is ideal in the house to wrap all the noise generating junk line cords and CATV cables thru. Ive spent several hundred dollars to de-louse my house and more out on all the feedlines and control cables using 43 and 31 mixes.

The material is all made by Fair-Rite Corp and you can get in depth details here.

http://www.fair-rite.com/newfair/index.htm

Carl
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KF6A
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« Reply #7 on: April 16, 2012, 12:48:26 AM »

........Best place to obtain these ferrite snap-ons?........
I've been getting mine from newark dot com. I've purchased lots of ferrite stuff from them. Very fast shipping.

On my vertical (80m-6m) I am currently using 4 or 5 (don't remember off the top of my head. it is what I had on hand at the time) #31 2.4"OD donuts and RG8X looped 5 or 6 times through the stack (again, not exactly sure and since it is raining and lightning outside, memory it shall be). When I replace my coax (hopefully soon) I have a "string of beads" (not snap-ons) of #31 on a section of RG213 to replace the donuts.

Read Jim's paper. It is worth your time.
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