RCM3000 generates RFI noise

Good Luck,

     We spend lots of money and time trying to snub this kind of stuff in order to obtain the CE mark for our products. Any circuit using a clock has the potential to cause problems, not just the Rabbit. Go to your Rabbitbios.c file and look for the ENABLE_SPREADER define and try setting it to 2 if it’s already, this may help you out with the noise. Other than that, ferrite’s like you mentioned or using good shielded cables may bring things under control. At that frequency, even a small opening in the enclosure is a potential source of RFI leakage, you could try using shielding tape around any oversized opening.  It’s tough to fix if you don’t have the equipment to test this type of thing….

Bob

Guys,

I'm having a problem with our RCM3000 equipped product generating RFI
interference.  Our product is a piece of electronics that is installed in
DOT style snow removal equipment, and it interferes with their business
band two way radios when they use frequencies close to the RFI generated by
the Rabbit  core.

We had a radio guy work with our equipment and determined with a frequency
counter that the biggest signal was at 151.0688 MHz.  Our entire
electronics package is enclosed in a grounded die cast aluminum case, with
several connectors to the outside of the box (including the ethernet jack
on the core).  From previous testing it appears to be bleeding out over a
9600 baud serial cable, which seems odd.  I assume that the signal must be
seeping out over the ground plane.  The only thing that runs at anything
close to that frequency is the clock on the Rabbit Core.  Most of the other
stuff is in the KHz range.

We're going to try to use some clamp on ferrite beads to solve the problem,
but I'd like to hear if anyone else has had problems with this type of
noise, and what they did to solve the problem.

Thanks in advance!

-Mike

You are right, it’s a science in itself and seems like “black magic” to most of us.

At 09:06 AM 9/27/2005 -0500, you wrote:
>      We spend lots of money and time trying to snub this kind of stuff in
> order to obtain the CE mark for our products. Any circuit using a clock
> has the potential to cause problems, not just the Rabbit. Go to your
> Rabbitbios.c file and look for the ENABLE_SPREADER define and try setting
> it to 2 if it s already, this may help you out with the noise.

Yeah we already did this on all our firmware.  It helped a little in some
cases, but obviously not all. >Other than that, ferrite s like you mentioned or using good shielded
>cables may bring things under control. At that frequency, even a small
>opening in the enclosure is a potential source of RFI leakage, you could
>try using shielding tape around any oversized opening.  It s tough to fix
>if you don t have the equipment to test this type of thing&.

I'm going to start bringing some equipment in house to try to nail this
down.  I'm going to start with a cheapy Uniden scanner which can act sort
of like a frequency scanner in close proximity (Close Call is what their
feature is called I believe).  That should at least let me hear the noise
and try to throw some spitballs at it to solve it.

If that doesn't work, I'm going to try to have a guy that knows a whole lot
more about radio stuff than I do look at it.

It's funny, out of almost everything electronic, RF stuff is the only thing
that I know little about and consider a "black magic" science.  Seems like
even the radio guys solve problems by trial and error.

Wish me luck,

-Mike