Carputer + RFI

[Crispin]

Who here is a fundi with RFI stuff?


I have an annoying RFI problem with my carputer. When it is on, most radio stations either vanish into static or sound like I am on the fringe and fade way into the hiss. BBC stations don't have a problem though. I am guessing they have better transmitters.


I have ruled out so far that it is not the monitor as that alone on does not affect it. The PC is in a metal box which is grounded to the chassis. The leads coming from the PC to monitor, passing close to the dash, all have a ferrite ring on them at the monitor end.

The PC case (http://linitx.com/viewproduct.php?prodid=12488) has perforations in for ventilation, but I would imagine they are too small to allow anything out. Non the less I will wrap it in tinfoil ( ) to test.
I will also power it externally to see if it is somehow feedback via the (switch mode) PSU.

Any one have any ideas on other things I can try?

 

[Jon Wildsmith]

You could do with a dip meter to wave about or just a portable receiver that picks up the RFI so you can see if it's just poor case screening or being carried out on one of the cables. If it is genuinly noisy then any of the cables including power could be the source and need ferrites. Chances are it's poor screening with that case though. I had a cubid perforated case in my 80 at one time that caused RFI on my HAM radio (didn't have regular radio) but it went away with the VRoom case and I don't get any RFI in the 100 with the same case.

 

[Andy Harvey]

To be honest the main cause of RFI is normally the power supply. Are you supplying the carputer from a dedicated connection to the battery or through a cigarette socket as they are often connected to the same circuit as the radio. Alternatively it could be that your power supply in the chassis is not shielded or is faulty. Unlikely that anything else on the MOBO would be causing large amounts RFI.

 

[Crispin]

Thanks chaps,

Seeing as I got baby sitting duty today, I've not had time to look at this yet. Mental note: Never take a 4 year old to Toys R Us.
I'll have a stab at it this afternoon and see.

CP

 

[Crispin]

So had a play around last night with it and wrapped in tin foil it is slightly better. Powered externally, it's the same as powered from the car.
When I powered it externally, there were no cables connected. Only the power which went to the adapter outside. This would indicate that it is RFI from the box itself and not via any cables.

Jon, that Voom box that you have, is it all ali including front and back panels?
What PSU do you use for yours? I have two spare mini ones which I will try and see if it's perhaps this one that is particularly bad. Failing that, I'll try the Voom case.

edit: How would the Voom case be better than my totally covered, grounded, tin-foil box?
edit: It's Voom, not vroom

 

[Crispin]

...and some more questions:
Yours is the voom and not the voom2?
are you using the M1-ATX PSU? It would appear that the case will accept a mini-itx board and the M1-ATX PSU (Which I have spare )

 

[TonyP]

Your tinfoil idea is not a bad one, but thinking back to my electronics days, I recall a Faraday cage was a bit thicker Now if you had a lead box you could put it into as a test that would be ideal....

 

[Jon Wildsmith]

vroom voom is steel bottom and end plates, aluminium top and sides. Not sure that foil is dense enough to be much of a screen to electromagnetic energy? I have a Yaesu FT-817D that's very handy for tracking down noise sources but any portable receiver that is affected by the RFI would do you just put the tip of the antenna near to different items to see which is loudest I use M1-ATX PSU's. I have a Voom & a Voom2 in the 100 I'm using the Voom and I was saving the Voom2 for my spare carPC which is in one of those none radio friendly cubid cases at the moment but you could borrow the Voom2 as I've been getting round to that for a while now

 

[Crispin]

I did not think a Faraday cage required to be a certain thickness. It is a grounded screen around something which gives an easier return path to any [stray] signals.
The whole lead thing is just because of it's density it does not....I am now contradicting myself.
Going off to read again. There's not much I remember from my ham radio exam


I am limited with the case I have now and the PSU due to size. I'll try the other PSU dangling out the box and see if it is any better, failing that, I'll take you up on the offer Jon. If it works, I'll send you a new shiny one (unless you oddly attached to this one?)

What I am confused about is what it is doing? RFI is normally heard as some form of interference. When the PC is on, it sounds like the radio aerial is unplugged. Just a weak signal.

 

[Jon Wildsmith]

A strong signal (RFI) will desensitize the receiver, bit like unplugging the antenna. It might not be a shielding issue and if you can wait till we happen to be in the same place at the same time I'll happily wave the antenna of my 817 about near your PC Not attached to that particular Voom2 but it's a bit bigger than a Voom (longer) so if it worked you might prefer a Voom or get me one, I'm easy either way if you go that route.

 

[Crispin]

Thanks Jon, I have a scanner I'll try. The problem with waiting is I am either forced to listen to Radio 1 in the mornings or my one and only CD. Both of which are boring now
I'll swap the PSU this weekend and see how it goes.

 

[Jon Wildsmith]

Can't you just leave the computer off to get other radio stations?

 

[Crispin]

I could - but I don't like other radio stations. There is only one that does not play annoying music: XFM
Besides, I will not be beaten by the computer

 

[Rob]

I could - but I don't like other radio stations. There is only one that does not play annoying music: XFM
Besides, I will not be beaten by the computer

I miss XFM, always loose reception after the Honda building on the M4

 

[Crispin]

I could - but I don't like other radio stations. There is only one that does not play annoying music: XFM
Besides, I will not be beaten by the computer

I miss XFM, always loose reception after the Honda building on the M4

Get your (rfi free) carputer and listen to digital

 

[MartinNaylor]

Mines the same, but mine is mostly the screen, its in front of the stereo and plugged in the lighter when in use.
It could also be something do with the computer being grounded too far from the battery, via the case and a negative to the battery. something like negative feedback or negative loop, but that was just trawled from the internet some while ago...
I now have a sony cheap version bluetooth stereo that supports A2DP and take the audio pc over the stereo using an A2DP Bluetooth dongle(belkin works but others dont). You can control media player to a certain extent from the stereo (Next Track/Previous Track and Pause).
Next i might try a digital radio reciever.
Not sure if you can get an fm one, but that might interfere as well...

Martin.

 

[Crispin]

I now have a sony cheap version bluetooth stereo that supports A2DP and take the audio pc over the stereo using an A2DP Bluetooth dongle(belkin works but others dont). You can control media player to a certain extent from the stereo (Next Track/Previous Track and Pause).

Now that is nice. I did not know you get that...

 

[Crispin]

So... I bought another case for the PC. One with a single fan and solid metal instead of a highly perforated one thinking that maybe the perforations are a bit OTT and letting all the nasties out.

Swapped everything and........still the same Contents of new case are all the same except the PSU which I swapped with a spare.
TBH, I was expecting it to not work because my previous attempts at wrapping it in tinfoil did not help.

Next option: rewire.

Instead of all the wires solder to each other I got a small ABS box and every locking connector off maplin's shelves ranging from 4 pin to 8 pin. Everything plugs into the box and the box does the joining of various bits (Camera power, reverse wire, override for camera, ignition for computer, override for it etc etc)
Everything now neat and tidy and plugged in. A couple of spare ferrite chokes I had lying around on the V+ and Ign to top it all off.

Test this morning:
No RFI! I can use the radio now without any noise / hiss or loss of signal.
Happy ( ) man.