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I am working on a Zigbee project and it will have to be sent in to a lab for FCC certification. I do not want to plop down the money for this blindly so I wanted to get some equipment here to pretest it to give an idea of whether it will pass or not beforehand. Anyone have experience in this area? I believe a Faraday cage and some sensors (but which sensors?)...

Thanks,
Kevin

The FCC is more concerned with what you are "putting" into the air rather than what you are "taking "out of it. They have set limits for modulation bandwidth, carrier power and carrier stability. Also They have limits on spurious emissions to be a certain DB level below the carrier.There are probably other restrictions but basically their concerns are will your device "play well" with other radio services. I don't think you will need a Faraday cage for testing, but you will need some very expensive test equipment such as power meters and spectrum analyzers and more. Also the test equipment may be required to have a recent calibration certificate to be valid.
Due to one time tests such as yours is the reason why independent test labs are popular. One option is to rent out the required test equipment for the time needed, but even that is not cheap.

Yeah... I saw a decent spectrum analyzer and it was $7000. I think I will find another way to precheck it. I believe the cert company can do that.

Thanks!
Kevin

if you are using an already approved zigbee module you probably won't have much problem but if you designed your own, it's wise to do a pretest. First understand the technical details of the tests you need to pass then focus on making cheaper mockups of the experiements. Asking here about general certification will result in only general answers. Most things (including recievers) only need to comply with part 15 but a transmitter will be more rigorous I assume.

Yes - it is a certified module. The test lab will do a pre-test as part of the testing procedure but I think it will pass right off.

Thanks,
Kevin

I suppose the antenna design is the place where the worst EMI mistakes can be made. A poorly engineered antenna could radiate unwanted energy even from a compliant transmitter. Resonant harmonics could appear at interfering frequencies or amplitudes. Using the certified module and the recommended design layout should result in proprer function. Zigbee is not a high power product and as such should be fairly tame.

If you enclosed it in metal or plastic with conductive paint, it should do a good job keeping the noise in.

You are probably in more danger from other elements of the circuit. Logic devices and switching power supplies can often radiate a lot of RF noise. A good Faraday cage will help a lot.

While clock and digital noise can be significant, it usually is not at a frequency used by trancievers. Woe be the designer who sets his CPU clock to 2400Mhz or exactly some other carrier frequency standard. The uncertainly about devices in this respect is what leads to the ban on all electronics during takeoff and landing of commercial aircraft.

Decoupling caps close to these clocked devices does a lot to reduce the transisnt switching noise emitted by the power traces. The caps provide a short path back to the ground pin of the same device for any transients, keeping them from radiating very far. newer lower power circuits also help in this regard by reducing the current in the switching transients. What can't be supressed by decoupling caps then may need to be shielded.

The antenna is a PCB antenna in this particular design so I am thinking (hoping) that it will work right out of the gate.

Thanks!