Hello, we have developed a project to transmit FM radio signals using a IC SI4713, but we believe that the problem is sometimes the IC Si4713 radiates FM signals throught the antenna and sometimes no. Why we conclude this? Because, at to put any other radio close to antenna from our device, sometimes it interfere the signal that we radiate from our device and sometimes no. However, at the testing laboratory where we have developed our project not happens that, but only at test outside laboratory. Which will be the problem? I attach an image of our device and antenna to test.

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  • We think that the ground of your PCB is very poor. 1, The top ground plane isn't connected with the bottom ground plane effectively, only four grounding vias are used for connection of top and bottom planes. You need to add many grounding vias for the connection. 2, a grounding via is needed to be placed very close the grounded terminal of the inductor of 120nH, maybe it is better to use a coil inductor for this 120nH inductor. 3,  The EPAD of the chip of Si4713 isn't connected with the bottom ground plane using more than five grounding vias.

    Also we think that a single wire is enough to form your antenna, don't use twin wires to do that.

  • Hello. Thanks for your reply.
    Do you recommend top ground plane and bottom ground plane? We don´t saw  top ground plane in AN383 SiliconLabs recommendations, but we will change the design to include it and will include the others suggestions.
    With respect to the antenna, only we use 30cm of a single wire wound like a coil, but i doubt the length of the wire until it reaches the coil. Currently, the total length is approx. 90 cm plus 30 cm of coil.

  • I had answered the ground questions. About antenna, you can use a single wire antenna of over 70cm or a wire wound coil antenna made from a single wire of over 70cm.