Author Topic: My Ferrite Bead Kit  (Read 620 times)

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Offline T3sl4co1l

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My Ferrite Bead Kit
« on: May 16, 2019, 08:22:01 am »
Contains only the most important items.  #43 and #31 beads, cable beads, snap beads (well, smaller ones, the bigger ones don't fit in here unfortunately), and some powdered iron cores for good measure. :)



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Offline coppercone2

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Re: My Ferrite Bead Kit
« Reply #1 on: May 16, 2019, 08:28:40 am »
Is this for commercial or home use?

Why do you say those ferrite beads are the most important?

Why specify a ferrite bead over a inductor with high SRF if cost is not an issue for one offs?

It's something I struggle to define.

I want to know how to think about the ferrite bead in a performance based regime that is unrelated to cost where the performance of the circuit can be improved over all other solutions by use of ferrite beads. Mainly because the product family is difficult to learn or is at least unconventional.

Mainly for PCB mount ferrite beads. I understand the snap on have their uses because its just a hack to make something work if you missed something or need to modify something. I mean for specification purposes. I also understand the little ones can interface with a through hole package in a unique way.
« Last Edit: May 16, 2019, 08:44:25 am by coppercone2 »
 

Offline floobydust

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Re: My Ferrite Bead Kit
« Reply #2 on: May 16, 2019, 10:33:25 am »
The hard part is knowing the frequency range of the material. AL does not interest me much.
I need to know 43 NiZn material at 100MHz, lossy or not.
With beads for through-hole part leads, like a mosfet or 1/2W resistor, does it saturate at a few amps or not.
This kind of thing I have to keep in mind.

I have a cable ferrite clamp-on kit from FerriShield/LeaderTech that has been good for solving EMI problems/drama out in the field.
At a 240kV substation, the SCADA D200 computer crashed from EMI when the breakers open and the arc. The burst comes in on all the yard wiring and corrupts all kinds of serial data.
At an EMC test facility, clamp-on's help to narrow down the radiator and mode for experimenting or when you need a last resort to pass.
 
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Online OwO

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Re: My Ferrite Bead Kit
« Reply #3 on: May 16, 2019, 02:51:06 pm »
SMD ferrite beads are often better for DC biasing (bias tee, etc) at RF than inductors. The FBMH1608HM102 for example has >200ohm impedance from 10MHz all the way to >3GHz. Try finding any 0603 inductor that approaches anywhere near that. The only time I would use an inductor for a bias tee is when I need to deliberately limit bandwidth.
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Online blueskull

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Re: My Ferrite Bead Kit
« Reply #4 on: May 16, 2019, 03:13:15 pm »
SMD ferrite beads are often better for DC biasing (bias tee, etc) at RF than inductors. The FBMH1608HM102 for example has >200ohm impedance from 10MHz all the way to >3GHz.

But it's lossy.

There are some high BW inductors, I recently just used a 47nH 2GHz choke on a GPS bias tee, and complimentary with it, I have a ferrite bead and a 10R resistor, connected in double pi network.

The result from my VNA is beautiful -- precise and deep notches on 1575.42MHz and 1602.00MHz, which means my bias tee didn't introduce anything other than the notches from the GPS module.
 

Offline Berni

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Re: My Ferrite Bead Kit
« Reply #5 on: May 16, 2019, 03:16:10 pm »
SMD ferrite beads are often better for DC biasing (bias tee, etc) at RF than inductors. The FBMH1608HM102 for example has >200ohm impedance from 10MHz all the way to >3GHz. Try finding any 0603 inductor that approaches anywhere near that. The only time I would use an inductor for a bias tee is when I need to deliberately limit bandwidth.

Ah didn't know about this trick. But don't the SMD ferites attempt to absorb too much of the power inside themselves? Or do they simply stop working as intended in the GHz range.
 

Online OwO

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Re: My Ferrite Bead Kit
« Reply #6 on: May 16, 2019, 03:27:03 pm »
The "loss" of a ferrite bead is simply that the impedance has a resistive part. If a ferrite bead has a 500ohm resistive impedance it behaves exactly like putting a 500ohm resistor in parallel. If you look at the attached graph you can see the impedance is >600ohm for much of its bandwidth, so any loss would be minimal. In terms of insertion loss it doesn't really matter whether the impedance is resistive or purely reactive, because both will load down the signal equally.
« Last Edit: May 16, 2019, 03:30:39 pm by OwO »
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Online OwO

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Re: My Ferrite Bead Kit
« Reply #7 on: May 16, 2019, 03:30:11 pm »
There are some high BW inductors, I recently just used a 47nH 2GHz choke on a GPS bias tee, and complimentary with it, I have a ferrite bead and a 10R resistor, connected in double pi network.

The result from my VNA is beautiful -- precise and deep notches on 1575.42MHz and 1602.00MHz, which means my bias tee didn't introduce anything other than the notches from the GPS module.
A 47nH inductor is useless below 200MHz or so, with impedance of still only 60ohms at 200MHz, so it's no match for the FBMH.
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Online OwO

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Re: My Ferrite Bead Kit
« Reply #8 on: May 16, 2019, 03:35:08 pm »
There is one case where resistive impedance is problematic, which is related to noise. If I did my math correctly a 500ohm resistance in parallel with a 50ohm path gives you -10dB noise power transfer, which is 10% added noise, or log10(1.1)*10 = 0.41dB noise figure. So in the GPS case an inductor is the better choice if it has less loss than the ferrite bead at 1GHz.
« Last Edit: May 16, 2019, 03:36:55 pm by OwO »
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Online blueskull

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Re: My Ferrite Bead Kit
« Reply #9 on: May 16, 2019, 03:37:49 pm »
There is one case where resistive impedance is problematic, which is related to noise. If I did my math correctly a 500ohm resistance in parallel with a 50ohm path gives you -10dB noise power transfer, which is 10% added noise, or log10(1.1)*10 = 0.41dB noise figure. So in the GPS case an inductor is the better choice if it has less loss than the ferrite bead at 1GHz.

Apparently you know MUCH more than me when it comes to RF ;).

I was just lifting from datasheet and adding tiny specs of spices here and there.
 

Offline T3sl4co1l

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Re: My Ferrite Bead Kit
« Reply #10 on: May 16, 2019, 09:47:24 pm »
Take a close look at the picture, "one of these is not like the others"... :D

Tim
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Offline T3sl4co1l

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Re: My Ferrite Bead Kit
« Reply #11 on: May 20, 2019, 01:44:52 pm »
No ferret fans in the house? ;D



Tim
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Electronic design, from concept to prototype.
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Online daqq

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Re: My Ferrite Bead Kit
« Reply #12 on: May 20, 2019, 02:40:37 pm »
I've got something similar, although after one nasty screw up it's labeled "EMI exorcism kit".
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Offline floobydust

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Re: My Ferrite Bead Kit
« Reply #13 on: May 20, 2019, 03:09:00 pm »
I thought it was a good luck skunk  :)
 


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