EMC

[Tagge]

Hi,
Im having a problem with transmitted (to CPU) EMC at lab.
If transmitting about 100MHz the CPU makes a reset?
Im using a 20MHz crystal, PIC 18F2525, and the powersupply is switched.
Filtred as recomended from supplier.
Is this a well known problem and at this frequency?
While measuring the powersupply it seems that its stable at this frequency, but..
Anyone have a good (or bad) idea
There is no room for large ferrits and so on..

[PCM programmer]

I made a board with a low power FM transmitter chip on it, that can
transmit at 100 MHz. I used a 16F871 to control the board.
This was a four-layer board, with power and ground planes, and
linear voltage regulators, running from a wall transformer.
I had no problems with the PIC resetting. I have done other
projects that used switching regulators, and have had no problems
with the PIC resetting.

I think the newer PICs are more sensitive to electrical noise than
the 16F87x series.

The PIC should have a 0.1 uF (100 nF) capacitor on each one
of the PIC's power pins. Put it very close to the pin. This is
standard procedure for board design. For boards that have
high frequency noise, it's often recommended to add a 0.01 uF
capacitor (10 nF) to each power pin.

I would also look closely at the MCLR circuit and the crystal circuit.

[Tagge]

You got a point there,
I havent filtered the MCLR at the CPU. I'm gone make some tests if it helps. The EMC testing is not any kind of a sience, its "magic, raindance and so on..", sometimes everything works fine and another time nothing is working. We also got a little high emitted EMC from the application, but it dont seems to have with the PIc to do. I havent got a good spectrum analyzer and thats a problem at pre testing. Have anyone used those cheep ones on the net, as the chinese AT5011 or the german handheld spectran, are these worth anything?
/Tagge