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I am building a device that consists of an ordinary WiFi router (WDR4300) as shown here:

enter image description here

Which works as a client and scans for networks OK when alone. The problems appear when I add another board to the case, which also contains a Texas Instruments AM3517/AM3505. The final design is shown below. The antennas are on the opposite side now and there is also a plastic case (not in the picture). But then WiFi performance gets very bad, it scans fewer networks with bigger noises and they appear weaker.

enter image description here

What do you think may be the problem?

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  • \$\begingroup\$ Have you disconnected the aerials from a conductive grounded chassis? \$\endgroup\$ – RedGrittyBrick Aug 9 '13 at 13:35
  • \$\begingroup\$ There is no conductive grounded chassis, they was screwed to plastic. \$\endgroup\$ – Pedro Ziff Aug 9 '13 at 13:58
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    \$\begingroup\$ As a first experiment, I'd try putting a grounded plate between the two boards. I'd also check those tiny coax cables to the antennae haven't been damaged or disconnected. \$\endgroup\$ – pjc50 Aug 9 '13 at 14:29
  • \$\begingroup\$ I have tried to put grounded plate in between also which was connected to routers USB ports ground. also to water tap (which< I think is perfect ground.) but still the same. Is there some method to measure what couses interference different way? \$\endgroup\$ – Pedro Ziff Aug 9 '13 at 14:41
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    \$\begingroup\$ At 2.4GHz, a "grounded" pipe isn't grounded at all. If you're trying to shield the radio from interference from the processor board, you'll need to completely enclose one or the other in a conductive shield, and beware of gaps and slots in your enclosure. A slot radiates just as well as the same length dipole. \$\endgroup\$ – Theran Aug 9 '13 at 16:18
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On the wdr4300 there is a portion on the PCB around the radios that is outlined, ready for a shield but there isn't one. I would recommend isolating the radios from one another by creating a small metal shield and soldering it to this outline. Take care to seal up the corners.

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