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GSM900_2nd radiated spurious emmision faild

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sivon

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hi guys,
the phone's 2nd conductive spurious emmision is ok, the performance is better than -40dBm, while the 2nd radiated spurious emmision failed. the peformance is even -2dBm.

would the kind-hearted guys tell me which parts can effect the RSE, thanks!
 

vfone

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Sometimes appear this problem especially when is using embedded antenna.
The radiated RF is going back to some circuits on the PCB generating harmonics, correlated with not decoupled quarter-wave traces that could behave like an antenna.

Another unusual case is when the gain of the antenna is much higher on harmonics compared to the fundamental (for multiband antennas).
 

sivon

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thanks very much! can the metal components near the antenna , such as speaker generate the harmonics?
 

xxargs

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sivon said:
thanks very much! can the metal components near the antenna , such as speaker generate the harmonics?

possibly, ferromagnetic material, iron etc. and high structural current can make magnetic fields strengt enough to working in unlinear area (near satturation) and this way make IM-products.

but check first if you not have 'simple' diode or simular thing klipping signal and make IM this way - for example LF-detect in amplifier to speaker if you have much structural RF-current around speakers etc.
 

vfone

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No! Metal components even if they have nonlinear characteristics vs RF power, is almost impossible to generate harmonics at usual power levels that you have in a portable device.
Semiconductors are the number one which generates harmonics.
 

BigBoss

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Metal components don't create directly the harmonics but they change the antenna impedance nonlinearly depending on power levels ( especially ferromagnetic materials ) and this returns back to the power amplifier and at the output of the PA, harmonics can occur..
 

sivon

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thanks all! if the conductive spurious emmision is good , is it useful to add the LPF circuits after the PA output? Our company does not have the standard EMC detecting system.is it meaningful to use the coarse probe to detect the source of noise? how to make the simple probes? thanks very much , guys!
 

vfone

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If the conducted spurious emissions barely meet the spec, a LPF could help minimizing the radiated harmonics.
At least with few dB’s, that sometimes might help to pass the radiated spec.
 

sivon

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does any one know how to make the coarse antenna ?thanks very much@
 

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