EMI shielding

[metroplex]

Forgot to ask:

how do I safely cut away that plastic that is covering the overbraid?

Do you think I should go w/ the drain wire?

 

[CaptnKirk]

I haven't found any pictures on the I'net that show how to do it, so give me some time to mod one, make some pics & I'll do an article on it.

Meanwhile, heres how I will do mine:

1) On the bench, you can slide the 'Boot Cover' (which is the peice that flares out over the connector) down and out of the way from the end you want to work on. This will be the middle of the two component cables (black & grey) or the single (black), as the BLUE goes to the motherboard header.

2) You can roll the insulation sleeve back over itself to expose about 1 inch of the overbraid.

3) Use a toothpick to open the weave of the braid and make a 'tunnel' through the braided strands.

4) Strip approx. 3/4" off the end of a 6 inch long drain wire, 24Ga to 28Ga, and slip the exposed conductor into the 'tunnel' in the braid.

5) Roll the insulation sleeve back down over the braid. This will capture and secure the drain wire in place.

6) Move the boot cover back to the connector end, & guide the drain wire out between the sleeve and the boot, bringing the wire out the back.

7) Strip approx. 3/8" from terminal end of thr drain wire and crimp on the terminal lug.

8) Reconnect cable into computer, Blue end to motherboard headed, Black to master - Grey to slave.

9) Connect the drain wire lug to any point on the chassis that is metal. A good point is one of the screws that mount an optical drive.

*Note: You can use 1 drain wire from a 2 unit connector, by using a 'daisy-chain' jumper wire to connect the upper and lower shields togeteher.

Foil inside the case serves no purpose, unless you have an all plastic case. the metal case already is a Faraday cage.

Nothing else needs the RFI/EMI grounging, as the cable shield does the job.

 

[metroplex]

FWIW I lined the inside of the case as well as the front bezel with 2-3 layers of foil (there's a huge hole in the front where the HDs are) and its helped radio reception when the comp is on.

BTW will fan grilles be enough to prevent excessive RF leakage at the fan holes?

So the major source of EMI/RFI is from the IDE and floppy cables?

I'll need 4 drain wires for two dual device ATA cables and 1 drain wire for the floppy?

I might get the cables later this week - so I'll see if I can mod them.

BTW someone told me that overbraided cables would increase interference because it adds capacitance... is there any merit to this statement?

Thanks

 

[CaptnKirk]

How can the Shielded cables add capacitance? They are NOT active to any circuit, all they do is capture stray radio waves and ground them out into the metal frame. This is exactly the way RFI/EMI is handled on the Space Shuttle and B-1 Bombers, and as a matter of fact ALL the other aifcraft flight and space flight vehicles. It works there, and will work in this simple computer system application.

 

[Bad Dude]

Hey captain,
Is that review coming soon?

 

[metroplex]

Kirk: sounds like a plan to me!

 

[Bad Dude]

Just so I get it clear once more .
All I have to do is to get the drain wire on the inner plastic part of the IDE cable? I do not have to put the drain wire directly to the copper wire from the IDE cable right?
Would it work without the twisted cables? How about the normal ribbon stripped and cover with aluminum foil then put the drain wire to ground it?
Thanks.

 

[CaptnKirk]

I'm sitting here playing with an IDE ribbon cable. If you use a pencil you can wrap the cable short end 2 times around the pencil
to make it kind of rounded, and doing the same with the long end you can go about 5 or 6 turns.

Now I think you could wrap a peice of aluminum foil around it,maybe like a 1 inch wide strip a foot or so long - or maybe more,
------------------------+
\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \|<-----{Wrap the foil in a spiral around the bunched up cable] (Creative illustration)
\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |
\ \ \ \ \ \ \ \ \ \ \ \ \ \= \|===========0 <---{Drain wire & lug]
------------------------+
and secure it with clear vinyl tape to secure and insulate the foil. Just before finishing the insulator wrap-around - you could
position a drain wire with the stripped 3/4" log lead end in contact with the foil, then finish wrapping the tape to secure everything.

The drain wire does have to contact the shield to make it work, dosen't matter if its a foil wrap or a braided shield. The TV co-ax cables
are done as twisted pairs with either a braid or foil wrap, foils works and is cheaper, braid works better - but costs more.

 

[Bad Dude]

Thanks Captain. I will give that a try.

 

[Morph]

CaptnKirk,

I'm wondering how much additional shielding this actually gives you and whether it's really worth the trouble. It seems that just by having braided cables, you are already doing much better than someone with regular ribbon cables or unbraided round cables. So if you had to take a guess, how much do you think braiding and a drain wire might contribute to shielding? For example, the presence of metal braiding might provide 60% EMI shielding and the presence of a drain wire might provide an additional 15% EMI shielding (just wild guesses with those numbers). Any idea on the real numbers?

 

[metroplex]

I asked my engineering professor (real swell guy that knows his industrial stuff) about the shielding and he says the drain wire must be in place in order for proper EMI shielding. It has to be part of the grounding otherwise it does nothing except make it look like something torn out of a space shuttle.

 

[Morph]

Hmm, the geek in me is insisting that i must have drain wires on my new round cables, but my lazy side is resisting. Of course the geek will win out.

You know, on the dual device cables you're gonna need two drain wires since there are two stretches of braiding that don't contact one another. So that's a drain wire for every single drive in your PC. Gonna be a pain if you have a lot of drives... and I do have a lot.

Please, someone tell me that Metroplex's professor is wrong

 

[CaptnKirk]

That's why I wrote the text on adding the grounding drain wire - to make the thing work.

 

[metroplex]

Morph: Yes i know about the dual device/2 drain wire deal.

I installed additional shielding for the front where there's a hole in front of my 5.25 bays

I used the plastic adapters that ship w/ the case, lined it with foil and attached a drain wire to that and the chassis.

For my current round cables I went with strips of foil attached to a drain wire, all wrapped in electrical tape for reinforcement.

to tell you the truth, the reception of my radio next to the PC increased and decreased...

im in the nYC area so I listen to WHTZ 100.3 MHz a LOT and its gotten significantly worse w/ these shielding mods.

HOWEVER 95.5 and 92.3 have increased substantially!
weird eh?

I'm waiting for SVC's cables to arrive before I work on them, the gEEk in me just wanted to experiment ahead of time with a cheap and easy shielding mod.

BTW i used 18AWG - I dont have such thin wires at home (26 and 28 AWG).

 

[Bad Dude]

Hi Captain,
I have done what you said but it does not improve my TV reception any if at all. I do notice that when I remove my TV card, the reception improves a little. Maybe I have a crappy WinTV card. I got a Happauge WinTV 401 Stereo TV card with remote. Any other ideas? Do you think a cheap or just average power supply will give the interference like that?
Thanks.

 

[CaptnKirk]

your Pwr Sply sound like it dosen't provide clean power. Don't think you can fix that - might need to replace it. Wait until you have done the round O'braid cable &
drain wire mod before going after the power supply though.

 

[metroplex]

Kirk: I tried the drain wire method but it just won't work that well w/ these SVC cables.

I got them and they appear top notch.

The ATA cable has twisted pair wires for the ribbon (actual twisted pair up to the plastic adapters) while the floppy is just normal ribbon w/ a nice braided insulator.

I can tell you this: using HD Tach 2.61, it appears my data is going a LOT better (not much interference) because the drive speed test has an actual slope and not a bunch of zig zags like a polygraph test (doesn't spike down to below 10 MB/s at all).

I think the braiding itself coupled w/ the twisted pair ribbon wire increased data integrity.

HOWEVER the first bootup resulted in a BSOF w/ an error in a device driver that has nothing to do with my PC (XP Pro SP-1) - the driver was TiCalc.sys used for linking my TI graphing calc to the PC.

Any thoughts?

BTW I can hear an electronic sound from my power supply.

Like when I flick the manual switch on and the Vsb kicks in (+5V/2A) I can hear something charge up (capacitors?) briefly.

When I shut it down, I hear the same sound (capacitors discharging into resistors??)

IS this a sign of a poorly filtered PSU? Or just normal operation?

It's an $80 500W ATX CompUSA power supply - so far its the only PSU that I bought that keeps the +5V above 5V for my AMD XP 2100+ running 13 x 139. Every other supply is 4.75-4.86V

 

[Bad Dude]

I just bought this power supply for $38 plus shipping. It got great features like the Enermax with fan thermal control, it also has the colored fan which was least of my preference. I was just looking for good cooling features with cheaper price. The power cables has gold plated ends and there were 8 of them all together. This is pretty heavy too. Here's a link to it. The price has jumped up to $48.99.
I don't think it's the power supply captain. How can I be sure?
I think it might be the TV card.

 

[Bad Dude]

I wonder if I have a UPS unit would solve the interference with the TV signal? Do you know captain?
Thanks.