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Author Topic: Position of Ferrite chokes  (Read 10009 times)
K2OWK
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Posts: 1035




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« on: June 14, 2011, 03:56:20 PM »

Hello, I have a problem with my computer keyboard locking up when I use my Ham transmitter. This occurs on HF bands and I have to reboot the computer to regain use of my keyboard. I have just purchased some snap on Ferrite chokes and was wondering where is the best place to put them on the keyboard wire? Should I place them one at the keyboard where the wire comes out and one at the USB connector where the keyboard plugs in, or should I place together at one point? I have not used Ferrite chokes in the past, but I was told this might work to cure my RFI on my computer keyboard. Any help would be much appreciated.

73s
K2OWK
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KI4VEO
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Posts: 166




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« Reply #1 on: June 14, 2011, 05:40:53 PM »

I had a similar problem with the keyboard and my mouse.  At the time I began my investigation I had no snap on ferrites but a good selection of cores used to wind rf transformers and baluns.

The problems with both the keyboard and mouse were resolved by winding 5 or 6 turns of the respective cables thru the cores very close to the end connector that plugs into the pc.  I would suggest positioning the ferrites there - perhaps more than one, if necessary.

This worked well until I added the Heathkit SB-1000 amp.  The problems resurfaced, with some additional ones, only on 40M.  I ended up winding a 1:1 coaxial choke - 25 turns of RG-8X around an empty plastic Folgers coffee can with the turns held in place with some Ty-wraps.  The common mode choke resolved all the problems.  The choke is pictured on my QRZ page.

Howard Walker
KI4VEO

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K2OWK
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« Reply #2 on: June 14, 2011, 08:41:12 PM »

Thanks Howard, It makes sense. I would guess you want to trap the RF at the computer input. I will try that tomorrow and let you know how it works out. I run barefoot at 100 watts.

73s
K2OWK
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K2OWK
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« Reply #3 on: June 15, 2011, 04:22:42 PM »

Hello again, I found the best position for the ferrite chokes was one at the keyboard where the wire exits, and one where it enters the computer at the USB. This eliminated my keyboard lock up completely on all the frequencies I use 40 thru 6 meters.

73s
K2OWK
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KI4VEO
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Posts: 166




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« Reply #4 on: June 16, 2011, 08:23:15 AM »

How is the mouse acting?  Any sporadic problems?

Your keyboard ferrite placement may be the result of using the USB port.  On my HP, I plug into the keyboard connector on the rear of the chassis.  In addition, the choking impedance of the ferrite snap-ons are probably much less than the cores I used.

In any case, glad it worked out for you.  If you install an amp someday and have problems, remember my Folgers coffee can choke approach.  Ugly, but it worked out.

All Electronics has a nice selection of ferrites at reasonable prices.  http://www.allelectronics.com/make-a-store/category/235/Ferrites/1.html

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K2OWK
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« Reply #5 on: June 16, 2011, 12:39:58 PM »

Hi again Howard, I have not had any problems with the mouse to date, just the keyboard. I will have to see what happens if I ever decide to use a linear amp on my station.

73s
K2OWK
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K1CJS
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« Reply #6 on: June 17, 2011, 05:13:49 AM »

Just a point of information.  On some of the more expensive keyboards made, there are built in ferrite chokes on the keyboard wire within a couple of inches of the plug that goes into the ps2/usb port in the back of the computer.  The newer keyboards that have built in processors for the extra control buttons on them may need a choke on both ends of its cable.
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AD6KA
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« Reply #7 on: June 27, 2011, 07:12:55 PM »

Quote
All Electronics has a nice selection of ferrites at reasonable prices. 
http://www.allelectronics.com/make-a-store/category/235/Ferrites/1.html

Yes they do,(and it's a fun place to shop in person!) but you don't know what
ferrite metrial you're getting. And there is only room for one turn on the "clamp on's"
two at the most of you have a thin wire/cable. My results with AE ferrites has been decidedly mixed.
So have results with those silly rectangular held-together-by plastic
ferrites from Radio Shack, HRO and others.

I'm glad the posted soved his problem. But if he runs into a tougher RFI problem,
which he WILL if he gets an amp, you really gotta get the real deal, the FT-240-43.
(or #31 material, wont debate it it here, #43 has worked wonderfully for me).
Like this, but you CAN find them MUCH cheaper with a little research
(I have seen them as low as about $8-9 each)
BUT THEY WORK! {/b]
The more turns you get on it, the more suppression.
This link is just a quickie for a photo, you can et them cheaper...

http://www.jpmsupply.com/servlet/the-475/Toroid-Core-FT240-dsh-43-Torroid/Detail

Yeah, they are kinda pricey, but last time  I checked, HRO wanted
$26.95 +tax for FOUR of those stupid, fairly useless square ones.
and Radio Shack wants $15 for TWO of them.
Ken,  AD6KA
As far as shack computer RFI, don't forget to check the cheesey wall
warts powering up cable modems and wireless routers. Clasic problems.
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KI4VEO
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Posts: 166




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« Reply #8 on: June 29, 2011, 11:11:06 AM »

"But if he runs into a tougher RFI problem, which he WILL if he gets an amp, you really gotta get the real deal, the FT-240-43"

Those cores are what I used on my PS2 cable for the computer mouse AND the keyboard.  The keyboard was getting squirrely on 80M and the mouse on 20M.  The cores solved the problem.  Got an assortment from a fellow on eBay...at a good price.  I tested some with a few turns of wire thru them and attached to my MFJ259B

When I added the SB-1000 amp into the mix, I experienced some RFI problems on 40M - not with the computer but my Mastech dual output power supply on the repair bench.  I could hear the relays clicking in the power supply, activated by the SSB voice peaks.  Yes, I could have just turned off the supply but the RFI would still have been floating around in here and I wanted to resolve the problem, if I could. My HP spectrum analyzer, with a short whip antenna, clearly showed the signal.  The Folgers coffee can choke solved that problem (a picture of it on my QRZ page).


 
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ND6P
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« Reply #9 on: July 21, 2011, 05:45:04 PM »

I had the same problem with a keyboard.  The keyboard had a straight USB cable, about 3 foot long.  I tried ferrites on the cable , but they did not work.  I changed the keyboard out with another that had a coiled cord, the same kind of cord that is found on many microphones, and that worked, without ferrites.  I think the coil on the cord doubles as an RF choke.  It also make for a neater installation.

73, Jim, ND6P
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KE7IZL
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Posts: 47




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« Reply #10 on: August 01, 2011, 07:03:23 PM »

Hello, I have a problem with my computer keyboard locking up when I use my Ham transmitter. This occurs on HF bands and I have to reboot the computer to regain use of my keyboard. I have just purchased some snap on Ferrite chokes and was wondering where is the best place to put them on the keyboard wire? Should I place them one at the keyboard where the wire comes out and one at the USB connector where the keyboard plugs in, or should I place together at one point? I have not used Ferrite chokes in the past, but I was told this might work to cure my RFI on my computer keyboard. Any help would be much appreciated.

73s
K2OWK

I had a similar experience 10 years ago or so with one of those small 50KV spark-gap Tesla coils you can get at a science hobby store. According to the instruction booklet it oscillates between 500KHz and 1MHz depending on where you have set the adjustment knob. I found that up to a foot away it would light a fluorescent tube (VERY STRONG RF here). So for safety I kept it at least 5 feet away from my computer. I also figured that since both my computer and the TC were plugged into the same outlet-strip and thus shared the same ground with very little length of conductor between any 2 outlets, and my computer's grounded metal case covers every square inch of the computer's internals, it would be safe. But it wasn't. Some times if the TC was running and I was using my computer at the same time I'd notice that sporadically my computer would "miss" a typed key, or a mouse movement, or even completely lose communication with the keyboard or mouse and I'd have to reboot the computer to fix it. One day I tried to turn on the computer, and it just simply didn't turn on. It seems that my keyboard and mouse wires (and also my body, who's hand was touching the mouse and keyboard) were acting like antenna, and I was unintentionally getting a strong RF signal into the computer. Even the power supply wouldn't turn on, suggesting that the the damage was likely in the power-enable circuitry on the motherboard that is supposed to trigger the ATX power supply's enable-pin. I wouldn't be surprised if a few other circuits were also ruined.
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K2OWK
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« Reply #11 on: August 01, 2011, 09:45:41 PM »

Just curious, Why would anyone run a Tesla coil in the same room as a computer? Why would anyone run a Tesla coil all the time? Why would anyone run an RF interference source (Tesla coil) at all? I would guess you were just experimenting with it, but that would be for just a few minutes at a time. It must have really played havoc with your TVs, Sterios, Radios and Ham sets, If you had one at the time and anything trying to receive RF signals. I am supprised you did not distroy all the electronics in your home at the time. Well I guess to each his own.

73s

K2OWK
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KE7IZL
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Posts: 47




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« Reply #12 on: August 01, 2011, 10:54:16 PM »

Just curious, Why would anyone run a Tesla coil in the same room as a computer? Why would anyone run a Tesla coil all the time? Why would anyone run an RF interference source (Tesla coil) at all? I would guess you were just experimenting with it, but that would be for just a few minutes at a time. It must have really played havoc with your TVs, Sterios, Radios and Ham sets, If you had one at the time and anything trying to receive RF signals. I am supprised you did not distroy all the electronics in your home at the time. Well I guess to each his own.

73s

K2OWK

It was a relatively low power one, with only 50kV output, not one of the 0.5MV output museum pieces. I was experimenting, and left it on for a bit while I go to look at instructions for an experiment on my computer. And since signal power falls off with the square of the distance, if it can light a fluorescent tube at a distance of 1 foot, then the field strength at 1 foot should be about 300V per foot, but at 5 feet that's 5 times the distance or 25 times weaker electric field or only about 12V per foot at a distance of 5 feet. The "faraday cage" effect of the computer's metal case should have protected it, as should have the shielding on the mouse and keyboard cables. Unfortunately the cables mustn't have been shielded adequately. Also it was like 10 or more years ago, and had less knowledge at the time.
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K2DFC
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« Reply #13 on: August 04, 2011, 10:10:17 AM »

I also had a keyboard RF problem when I tried to extend the cable for more versatility. Computer locked up every time I hit the key. Got a wireless keyboard. Problem solved. I can also move it anywhere without cables to get in the way.

K2DFC
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W8JI
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« Reply #14 on: August 04, 2011, 10:53:15 AM »

This is like standing up in an auditorium and asking people how to do brain surgury. :-)


For HF the proper core mix is 73 or 77 materials, not stuff down in the 60's or 40's. A 31 or 33 mix might also work, but they are special mixes.


What you want is a mix that looks purely resistive at HF, not some VHF suppresson material that is inductive at HF.

You would be far better off to find out if or WHY you have excessive RF in the shack then throwing beads on things. Often times antennas lack baluns, or have the wrong type of balun or feed system, or there are other problems and keyboard or computer problems are an indicator of a problem elsewhere.

If you hand is near the item and it acts up, and if the item is OK when your hand is away, it will be very difficult to cure with beads or cores. That is almost always a serious design problem inside the device, or a serious antenna system problem.

http://www.w8ji.com/rfi_rf_grounding.htm


73 Tom




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