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Author Topic: Ferrite Beads for coax current chokes #Type/Amount?  (Read 11148 times)
K1WJ
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Posts: 505




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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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G7VGG
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« Reply #8 on: August 22, 2015, 04:25:36 AM »

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. :-)

Actually, whilst 31 and 43 material both work at up to 300mhz, 31 material works significantly better at both lower and higher frequencies than 43 material.
31 material can be used over a much broader bandwidth than 43 material so its better for multiband antennas, especially HF antennas.  31 material can be used from 1-300mhz but I have seen some references saying 31 material is good for up to 500mhz! 
Fair-Rite itself, who make such beads in both materials claim its good up to 300mhz, so that's probably the most accurate frequency reference to go by.
Fair-Rite say 43 material is only good for 25mhz up to 300mhz, making it virtually useless for use on any band below 10m!  Not only that but the choking impedance of 31 material is also significantly higher than 43 material.
Fair-Rite use a standard reference frequency of 100mhz to measure they Ferrites impedances.  A single Fair-Rite 2643626402 Ferrite core (a 43 material slip-on/pass through Ferrite sleeve (suitable for use with RG8 or M&P Ultraflex 10 coax) with the following dimensions 18.7mm OD, 10.15mm ID, 28.6mm long, only manages 196 Ohms at 100mhz, whereas the identically sized 2631626402 core, made of 31 material, manages a significantly higher 225 Ohms at 100mhz.  So I would never recommend the use of 43 material over 31 material, unless cost is critical...31 material does cost a bit more, but its worth it!
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W1VT
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« Reply #9 on: August 22, 2015, 04:47:44 AM »

http://www.karinya.net/g3txq/chokes/
According to Steve's measurements, 17 turns on an FT-240-43 is a very nice balun for 80/60/40 meters, even edging out 17 turns on a FT-240-31, though the latter is better for 160M.

But, who knows what else can be designed with these materials?  Even the manufacturer can't predict that!

Zack W1VT
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G7VGG
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« Reply #10 on: August 22, 2015, 05:05:29 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?

It really depends on the diameter of the coax your going to use...Larger diameter coax has less loss that smaller diameter coax and very usefully, larger ferrite beads have higher choking impedances than smaller ones...So your going to be better off using larger coax and larger beads.  
To find the best beads for the job, first you need to use a digital Vernier to accurately measure the average diameter of your coax.  Take several measurements along several feet so you can round up the figures to get an average diameter.
In my case I need a choke to stop RF in my shack when using my 2m Slim Jim, which is on a 35 foot fibreglass mast.  I use high quality, Italian made, M&P (Messi & Paoloni) Ultraflex 10 coax, which has an average diameter of 10.1mm.  The best size bead is one that can just slip over your coax with a tight sliding fit, so it stays put without needing glue to hold it is place.  I chose Fair-Rite 2631626402 Ferrite cores/beads, because their internal diameter is 10.15mm, just right to slip over the Ultraflex 10...In fact, the fit is so tight I had to smear the coax's outer sheath with a dab of Vaseline to get them to slide on easily.  I used a suitable length of 20mm ID heat shrink to hold them all in place and to finish it off and ensure my sleeve-choke stays weatherproof I sealed the end of the heat shrink with self amalgamating tape.
I spaced the 10 beads 10mm apart to allow the coax to flex where the sleeve choke is fitted
Note: the third and forth numbers in the Fair-Rite part number above refer to the material used to make the bead...In this case, 31 material...The best material to use from 1-300mhz.  At 100mhz each of the latter beads gives 225 Ohms choking impedance.  The identically sized bead made from 43 material (2643626402) only manages 196 Ohm at 100mhz.
So five 31 material beads will give you over 1000 Ohms choking impedance at 100mhz but you would need at least six 43 material beads to exceed 1000 Ohms C.I.  So whilst 31 material beads cost a bit more than 43 material versions, you don't need so many of them which can help even out the cost. Smiley

« Last Edit: August 22, 2015, 05:09:28 PM by G7VGG » Logged
N8CMQ
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Posts: 600




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« Reply #11 on: August 22, 2015, 07:23:00 AM »

Ground mounted you said?

Bury the coax and don't worry about it.

There will be little current on the coax if you bury it.
I ran my coax through 100 feet of armor flex conduit and buried it
one foot deep. the armor flex is to keep rodents from chewing the
coax. It also keeps current attenuated on the outside of the coax.

After many years, everything is still going well, except the radials.
I need to replace the radials soon. All 130 of them!
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N8CMQ   Jeff Retired...
E73M
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« Reply #12 on: August 22, 2015, 07:43:27 AM »

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

3000 Ohms is more like bottom minimum. Yes, you need Balun/Choke even with coax in the ground and good radial field.
As some mentioned, For 6-20m  #31 is ok but if you wind too much turns it is useless on 20-6M.
For your case, the best option is 8-10 Turns on FT240-43.
 LMR240 could pass thru it and does not need to be tight around the core.

73 Danny N4EXA aka E73M
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Daniel "Danny" Horvat, N4EXA aka E73M
www.E73M.com & www.MyAntennas.com
N8CMQ
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Posts: 600




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« Reply #13 on: August 22, 2015, 07:49:42 AM »

Yes, you need Balun/Choke even with coax in the ground and good radial field.

73 Danny N4EXA aka E73M


Really?  Shocked

You measured how much current with your current probe?

I measured 0 amps of current on my coax, and that was 80 meters to 10 meters.
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N8CMQ   Jeff Retired...
E73M
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« Reply #14 on: August 22, 2015, 11:35:02 AM »

Yes, you need Balun/Choke even with coax in the ground and good radial field.

73 Danny N4EXA aka E73M


Really?  Shocked

You measured how much current with your current probe?

I measured 0 amps of current on my coax, and that was 80 meters to 10 meters.

Yes, Really Smiley
If you measure current at radio side of coax  it will show zero or some, depends on coax length and radial number. But, at feed point or few feet from it might give you some reading.
So, if current on the outside of the coax shield dissipates along the cable and not being radiated by the vertical side of the antenna, I would say that verticals need BALUNs too.
Another good reason is to prevent induced or any other noise traveling on your grounding and cable shield to enter your receiver via differential mode. 
On my antennas, I have 3 or 4 Baluns/ Chokes along every cable and good BALUN on the 160m vertical antenna.
BTW my all cables are underground.

73 Danny E73M

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Daniel "Danny" Horvat, N4EXA aka E73M
www.E73M.com & www.MyAntennas.com
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