Ty-Raps around the cable on either side of the ferrite is a pretty quick and simple way to hold the ferrite in place.
I have a problem of RFI effecting my laptop
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steve-kc7byp
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1st off I would like to thank everyone for throwing their 2 cents in the pot. Sometimes it takes more then 1 mind working on the project to solve it. In this case the tech at Palomar Engineers told me that if the ferrite is to big for the cable then put electric tape on the cable to hold the ferrite in place. It works. There is no more RFI getting into the laptop via the USB plugin devices. Problem solved. 
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1st off I would like to thank everyone for throwing their 2 cents in the pot. Sometimes it takes more then 1 mind working on the project to solve it. In this case the tech at Palomar Engineers told me that if the ferrite is to big for the cable then put electric tape on the cable to hold the ferrite in place. It works. There is no more RFI getting into the laptop via the USB plugin devices. Problem solved.
Instead of tape, I put a cable(zip) tie around the cable at each end of the ferrite with them up tight against the piece you normally cut of the cabe tie up close to the ferrite (I then trim the pull tie leaving enough of it to do the job). It is neater and more durable than the tape.
ecps92
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KC4RAF
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Many a times used ty-raps. Much better than tape, and as ecps92 posted, does not leave that sticky adhesive on the cable or ferrite. And ty-raps are cheap at Wally world and else where.
steve-kc7byp
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Just for info. the ferrite is over the spot were the tape is. But yes the wire ties are better then tape and it is not like I have a shortage of wire ties.
KC4RAF
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Yeah Peterwo2e, that's what we like about RR. If you have a problem, do a search here and you generally will find the answer, or post a question as Steve did, and many will come to the podium and help you try to solve your headache.
For the price to join RR, you just can not go wrong. (FREE or the Premium Subscription which is still cheap). (man have I went over board just to say how nice RR is!!!)
For the price to join RR, you just can not go wrong. (FREE or the Premium Subscription which is still cheap). (man have I went over board just to say how nice RR is!!!)
steve-kc7byp
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I have a problem of RFI
Peter, that's an interesting idea. looping turns of the cable around a dead AA battery. I will have to add that one to my little bag of tricks notebook. Thanks.
Peter, that's an interesting idea. looping turns of the cable around a dead AA battery. I will have to add that one to my little bag of tricks notebook. Thanks.
wb6uqa
Member
For RFI ferrite snap-on cores work like RF chocks.
You have to pick the right ferrite mix snap on core and wrap it with the right amount of turns to be effective at the frequencies you want to snuff. The typical snap on cores you find that fit wires 1/4" to 1/2" dia do absolutely nothing for HF frequencies and even for VHF interference (like 2m amateur) you need at least 2 to 3 of them in series or 2 turns of the wire through one of them. These are usually a type 43 mix ferrite.
To be effective you need to introduce at least several thousand ohms of impedance at the interfering frequency without affecting the desired signal passing through the filter. A single small snap on core provides maybe 150 to 200 ohms impedance by itself. Every time you double the turns the inductance goes up four times, so if you wrap 2 turns through it (if it fits) and now you might have 600 to 800 ohms impedance but with a 43 mix small snap on the effective frequency range might be 30 to 200MHz and not much good at HF.
You can add several small snap on cores in series along the wire, each wrapped with a few turns (if they fit) and that will contribute to the overall impedance and lower the effective frequency range, but it will be hard to reach the several thousand ohm range with small snap on types.
For fixing HF interference a 31 mix is better and you need a good 8 to 10 turns of a power cord or speaker wire through a large 2.4" dia ferrite toroid core to be effective. There are huge snap on types in a 31 mix for HF with center holes between 3/4" and 1". These are great because you can open them and usually get enough turns of power cords or speaker wires to be effective at HF without disconnecting the cable. The only drawback is they are expensive at $10 to $20 each. A 2.4" dia 31 mix ferrite toroid is about $9 in comparison but harder to work with.
prcguy
To be effective you need to introduce at least several thousand ohms of impedance at the interfering frequency without affecting the desired signal passing through the filter. A single small snap on core provides maybe 150 to 200 ohms impedance by itself. Every time you double the turns the inductance goes up four times, so if you wrap 2 turns through it (if it fits) and now you might have 600 to 800 ohms impedance but with a 43 mix small snap on the effective frequency range might be 30 to 200MHz and not much good at HF.
You can add several small snap on cores in series along the wire, each wrapped with a few turns (if they fit) and that will contribute to the overall impedance and lower the effective frequency range, but it will be hard to reach the several thousand ohm range with small snap on types.
For fixing HF interference a 31 mix is better and you need a good 8 to 10 turns of a power cord or speaker wire through a large 2.4" dia ferrite toroid core to be effective. There are huge snap on types in a 31 mix for HF with center holes between 3/4" and 1". These are great because you can open them and usually get enough turns of power cords or speaker wires to be effective at HF without disconnecting the cable. The only drawback is they are expensive at $10 to $20 each. A 2.4" dia 31 mix ferrite toroid is about $9 in comparison but harder to work with.
prcguy
Bad idea. Dead batteries will eventually leak the caustic chemicals inside, which will probably damage your computer.
KC4RAF
Member
I believe he wrapped the wire around an old AA outside his computer. He wouldn't have enough room inside the mouse or computer to do as he posted.
There are no magical RFI reducing properties in a AA battery. Anything else made of steel would have about the same inductive loading properties added to a coiled wire, which is not much.
prcguy
prcguy
Carbon might look a little like ferrite but that's where the similarity ends. Plus its wrapped in steel which counters any properties the ferrite has. Take a nice effective ferrite rod choke and wrap it in a thin steel case and you now have the same choke as some wire wrapped around a bolt, which is has no more RFI absorbing properties than the same wire wrapped around a steel bolt.
prcguy
prcguy
KC4RAF
Member
+1 with prcguy. The steel or iron will stop the actions that the carbon would've had.
An example I can think of is:
An old time AM radio that had the ferrite rod with all those turns of ~32 gauge wire for the antenna. The steel wrapped around it would decimate the action of the rod.
An example I can think of is:
An old time AM radio that had the ferrite rod with all those turns of ~32 gauge wire for the antenna. The steel wrapped around it would decimate the action of the rod.
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