My controller Malfunctioning due to Radiated Emision of 350Mhz Walkie Talkie device

Hi all,

My controller is Malfunctioning when i bring the 350Mhz Walkie Talkie Equipment type: Motorola GP328 Plus 350mhz , Model No: AZH38PDC9AA3. What are the Ways to arrest the Radiated Emission. Please recommend.

Is there any filter or component or shielding Materials to arrest this frequency. Please let us know.

Regards,
V. Prakash

Hi,

The problem most probably is not the wakie talkie. It needs to send the frequency with the necessary power to be able to communicate.

The problem most probably is that "your controller" design is not EMC compliant.
I recommend to modify "your controller".

Klaus

Hi,

what are the modification i have to do with my controller to have a EMC compliant. please let us know.

Regards,
V. Prakash

It is not possible to tell you what modifications you need to do as only you know what your circuit is. It's like saying my circuit doesn't work; why?

Designing for electromagnetic compatibility is a very important ( I would say vital ) skill to have.
You need to identify the part of your circuit that is vulnerable then remove or reduce that vulnerabilty.
There are plenty of resources on line ot help you, just search for something like design for electromagnetic comatibility or EMC basics

Hi,

I had already fininshed designing my Product. Now i have to change my whole design is a huge task. So please recommend any shielding or
Filters available to arrest this type of noise.

Regards.
V. Prakash

Hi,

First and - in my eyes - the most important is a really solid GND plane. Best: No splits, no other wires in it. All the signals refer to this signal and it should have the same potential at every time (HF) at every place.
Decoupling capacitors at every IC supply pin.
All board_IOs need to have EMI/EMC filters and ESD protection. This might be R, RC, LC, common mode filters, HF suppressing EMI inductors.....

Klaus

I know that hind sight is a wonderful thing, but designing in EMC immunity from the start is the only way to go. Trying to retrofit a solution can be difficult and expensive, this is, or was the first thing they teach you in EMC classes.

You don’t actually say what is causing your problem, this would help in giving you some quick fix advice.
Everything Klaus mentioned is all sound advice. Being perhaps a little more detailed for high frequency immunity and assuming that it is an op amp input or low voltage digital input that is giving the trouble try putting a series resistor close to the input and perhaps a capacitor from input to ground or whatever the input may refer to as ground. As to values that will be circuit dependent, again making the assumption that fast response is not needed for a 350MHz interferer 1nF would be more than enough for the capacitor, 100 to 1kohm should do for the resistor.

If you have any long leads connected to your circuit this will be a good way for the signal to get into the unit, a 25cm lead length makes a very good antenna at 350MHz.
All this is quick fix stuff, if you want to place your unit on the market it really needs designing for a hostile EMC environment, even if your local regulation do not require it. The product and your company will soon get a reputation for being unreliable, and depending on the application dangerous.

If you place your uC circuit in a metallic closure, I believe your problem is solved.

I would also consider - along with above tips - as an additional protection (although not totally sure of its effectiveness), a grounded heatsink right above the microcontroller as wide as possible, regardless of its actual thermal need. This may somehow provide a shielding, not for the uC, but to the tracks routed in its vicinity against an environment immersed in harsh EMI.

Hi,
My controller is already in a metal enclosure.

Regards,
V.prakash

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Hi,
Shall I try this attached 350mhz absorbent sheet. Pl. Let us know.

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Hi,
Image re-attached for clarity.

Regards,
V.Prakash