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Author Topic: Beads, not like New orleans, but Ferrite beads  (Read 1492 times)
KC3BBI
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Posts: 40




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« on: May 18, 2016, 04:20:45 PM »

I took apart and old cable and found some ferrite beads to use on the antenna cable. I do not know the type or mix number. I want to apply a choke balun or beads I dont know if it will work whether it is made for a different frequency.
I would like to know do the beads work from any sort of mix? They are only about 1/4 inch so they would have to be installed on the center conductor of the coax cable.
From what i understand in school I was taught that the maximum power passes when the reactance = 0 and resistance is only from the load.  So, in application i must be looking for the reactance to cancel any capacitance or inductance that are not = 0.
Am i correct?
I would like to know about the types and applications. Can anyone help with a link to helpful webpages or information? I would like to know how many and what type beads to use.
I have the MFJ 259c analyzer to test reactance. So if i need to test for reactance after using the beads then i can test it.
Where do i find a list of beads types and where to buy them?
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W9IQ
Member

Posts: 549




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« Reply #1 on: May 19, 2016, 04:05:43 AM »

Bob,

To use ferrite beads to make a balun they must be fitted over the braid of the coax, not the center conductor. And it takes a lot of beads to make an effective balun this way. It sounds like your reclaimed beads are not fit for your intended purpose.

If you are interested in making a choking balun, you would be much better off winding some coax through an appropriate ferrite toroidal form.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
WX7G
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Posts: 6993




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« Reply #2 on: May 19, 2016, 05:03:12 AM »

To test the beads loop a short length of wire (4" for example) thru the bead and connect the wire from the MFJ-259C ground post to the UHF connector center receptacle. Dial the frequency around and record R and X. The impedance magnitude is the square root of the quantity R squared plus X squared.

To make a coaxial feedline choke the beads are slipped over the outside of the coax and a starting point is to use enough beads for a total of 2000-4000 ohms. This can reduce the RF current on the outside of the coax. Here's an example using a dipole:

A dipole is fed with coax and one one side the center conductor connects to antenna wire 1 and one the other side the shield connects to antenna wire 2. The antenna consists of antenna wire 1, 2, and the coax shield. You have a three wire antenna. By adding impedance to the outside of the shield at the antenna the antenna consists of wire 1 and wire 2.

Your beads are too small unless you plan to use RG-174 (or some other small diameter coax) so you might just string them together and have some fun at Mardi Gras.
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NK7Z
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Posts: 1424


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« Reply #3 on: May 19, 2016, 05:31:58 AM »

This link will tell you more about ferrite beads than any other place on the net...

http://audiosystemsgroup.com/RFI-Ham.pdf

The guy lives this stuff, and is really good at it.  Take a look at his choke construction articles as well...
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
KC3BBI
Member

Posts: 40




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« Reply #4 on: May 19, 2016, 09:10:01 PM »

Thank you guys
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KC3BBI
Member

Posts: 40




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« Reply #5 on: May 19, 2016, 09:27:11 PM »

actually i was looking for comparison like this one.
http://palomar-engineers.com/ferrite-products/ferrite-cores/ferrite-mix-selection
thanks for the info guys.
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AA4HA
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Posts: 1999




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« Reply #6 on: June 16, 2016, 04:30:57 PM »

I got some beads in New Orleans, I will not go in to what led up to guys tossing strings of beads to me.  Wink
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
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