power supplies with minimal radio interferance?

**Mickz** · 11-23-2010, 04:13 AM

Hi, apart from mine stuffing my GPS, my other concern was DAB and FM radio.
I have one arriving soon, I hope.

Just ran a test with a shielded receiver on FM and a small 5” pickup wire.

You can touch the PSU shielded case with the pickup wire, you can run it over every PSU
lead going to the MB and there is no trace of PSU noise. And that’s with the lid off.

One lead draped into the box and you have the interference back. Dam it works well, only noise is a little from the PC.

BTW: The noise from the M4 is somewhat voltage dependant and gets really bad as you
approach the transition from 12v cut (regulate) to boost. Best of luck, it’s worth doing.

**Chester** · 11-23-2010, 07:32 PM

Just to check, you have said 0.001 feed through caps, that would be 1000pF then?

Just looking at the mouser ordering page, and there are a heap of different ratings!!

Fair difference in price too, some are cheap as chips, some are chesthurtingly expensive

**Mickz** · 11-23-2010, 08:03 PM

Yes, 1000pf is correct; my old unmarked unit’s read around 1130pf.
Standard value though is 1000pf.

If you’re unsure, just post or send me the links to the ones you’re looking at and I’ll
have a look at the specs.

The bolt on ones will be cost slightly more, however the biggest price variation would be
in voltage rating. In this case it doesn’t matter, I doubt there would be any rated below 20
volts.

You may want to choose a slightly beefier unit (thick through lead) to give a strong mounting
point for the cables.

**Chester** · 11-23-2010, 08:09 PM

Looking at 2 of them, both are rated for way in excess (200V for one, 500V for the other!):

$9.60 for one: http://au.mouser.com/Search/ProductD...3WFD%2fw%3d%3d

$4.21 for one: http://au.mouser.com/Search/ProductD...JaiSamRA%3d%3d

The second one looks about right for the job from what I can see.

**Mickz** · 11-23-2010, 08:36 PM

Ok, it comes down to the robustness of the terminals.

You have four fairly thick +5v leads to solder on to each end of the cap
.
If you are careful and tie the external cables securely so that no tension
is placed on the connection then the lower cost units should be ok, the $9
unit is slightly stronger, however any will work.

I used nine feed through caps on mine. I’m surprised at how costly these are getting.

Don’t’ know any old hams with some old valve junked gear? These were used a lot in the past.

Just to make you feel better about the cost, I buttoned mine up and powered the PC up.

I can sit a small FM radio on a weak station on top of the power supply.
There is absolutely no PSU noise – the only noise is the standard PC noise.
At one foot distance there is nothing from the PC either; and its out of the case.

**Chester** · 11-23-2010, 08:56 PM

Cool, I'm happy to spend more on the more expensive ones, even allowing for around 10, thats still not a huge cost overall, for what sounds like a huge improvement.

I will mount a strain relief on the outside cable to remove any chance of me yanking the cables off the caps, that will be easy enough to do, and should also make it look neater, as I can use shrouding on the cable to make it look all nice and pretty, and tie that in with the strain relief tiedown.

Awesome, got a few evenings of fun ahead of me now, I'll post up how I go! hahah

**mitchjs** · 11-23-2010, 10:39 PM

this is good... there are some cheap feed though caps on ebay
http://cgi.ebay.com/2pk-1000pf-Feed-...item5ad7fe0a87
look like solder in

maybe just some pcb mounted feed though caps would work

worth trying, could make a pcb that plugs right into the output plugs of this
that has the caps, then another set of plugs...if you follow my idea
http://www.avx.com/docs/Catalogs/w2fw3f.pdf

**Mickz** · 11-24-2010, 03:15 AM

Originally Posted by mitchjs

this is good... there are some cheap feed though caps on ebay
http://cgi.ebay.com/2pk-1000pf-Feed-...item5ad7fe0a87
look like solder in

maybe just some pcb mounted feed though caps would work

worth trying, could make a pcb that plugs right into the output plugs of this
that has the caps, then another set of plugs...if you follow my idea
http://www.avx.com/docs/Catalogs/w2fw3f.pdf

Yes, solder in but look nice and strong.

The smaller ones in the PDF appear to be severely current limited.

**mitchjs** · 11-24-2010, 08:49 AM

oh, duh... i forgot about current... we got some major amps here

it was a thought

**Mickz** · 11-26-2010, 01:03 AM

Update, the M4 in shielded case is on a par or better than my expensive AC powered PSU.

Instead of getting No GPS signal in the car, I now get about half the satellites, but at
a reduced level, it works though. FM in the car is now 100% instead of just noise.

Testing on the bench revealed that the GPS receiver was not going to work to its full
potential in close proximity to the PC-PSU and SSD drives don’t help either, although this one
is pretty quite compared to others. So I bit the bullet and moved the CAR-PC into the boot.
No loss of video quality with a good quality 15ft VGA lead. I now have perfect coverage with
the tiny USB GPS receiver hidden under the centre dash at the base of the windscreen.

Because of the M4 mods there is no crap running down the leads from the boot. I’m not
expecting to have any problems now with DAB when the receiver arrives and the audio
system, when installed, should also benefit from the quite supply.