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Radiated Emission from 125MHz and their harmonics

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amrendra2k1

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I have gone for prescan of our board to an semi anehoic chamber and we found that radiation mentioned by me above is due to a RGMII_TX/RX_CLK line which is 11inch long trace. RGMII_Clk line trace is made(11inch) intentionally to add delay of of 1.5/2ns which is required between data and clock line as per RGMII specification.
These lines are also going through a board to board connector.How we can reduce the radiation due to RGMII_TX_RX clock line?
 

How do you know, that the emission is from the clock line rather from digital devices generating or controlled by the clock, and their power supply?
 
Hi FvM, when we disable this particular clock line radiation comes within the limit?
 

To prove, that the (i guess microstrip) line is causing the emisions, I would replace it by a semi-rigid coaxial line of same delay. Generally, an open microstrip line has some radiative dispersion and may possbly make the ground plane radiate as well, depending on the board geometry. You should try to replace it by a lumped delay, e.g. a LC circuit, or a buffer.
 

You could place copper tape (grounded) over the track to see if a buried line would be better.

Keith
 

You can try to use microwave absorbers - like some rubber-kind pieces placed over the trace or in the enclosure. Depends on the application.
 

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