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I bought an ADF4350 PLL board from china. On the board there are 10 pins (programming and supply) which are connected to my BLE board (with an integrated antenna).

Im observing following problem:

When the PLL board is connected and output a signal (let's say 2.48 GHz, and not to the BLE board), my BLE board has a much worse sensitivity at this frequency. The 10 pins on the PLL board are connected over a ribbon cable with the BLE Board. When I put the cable on a ferrite ( unfortunatly I don't know what kind of ferrite it is) the sensitivity gets better but still not as good as without the connection to the PLL board.

Now my question:

Are there any types of ferrites which will have a high enough impedance at this frequency range to prevent this?

Or is there a better possibility to fix this?

Best regards

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  • \$\begingroup\$ A data sheet for the china module would be useful. \$\endgroup\$
    – Andy aka
    Commented Jan 24, 2018 at 16:45
  • \$\begingroup\$ It it is like this : alexnld.com/product/… unfortunatly there is not datasheet per se \$\endgroup\$
    – epgrape
    Commented Jan 24, 2018 at 16:50

1 Answer 1

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It sounds to me like the power current for the ADF4350 module contains a significant level of RF current i.e. current at 2.48 GHz and this will get onto your BLE board because of the 10-way ribbon connection. What I would do is make a better interface cable that more thoroughly stopped the leak-back of RF currents. You could try experimenting with more ferrites but you might get to the point when you can't fit any more on the cable and then you might need to design a little satellite board that had common-mode and differential inductors on board that choked off the RF from getting back to the BLE board.

If you continue down the ferrite route look for ones that have high losses at 2.5 GHz.

You might also try using some Aluminium foil around the cable and connecting it to earth at the BLE board to see if that stops problems or makes things better when you can't add any more ferrites.

Sometimes you have to try several things together to reduce the problem to acceptable limits then try removing each measure and see how effective it was. That's EMC a lot of the time.

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  • \$\begingroup\$ I have tried the aluminium foil suggestion but with no success. I have also found an answer of @stevenh where he said that you can use 22pF capacitors or ferrite beads to suppress HF signals. For now I just tried it with 22pF capacitors with little success. I guess the ferrite beads will do it. edit: sorry that I did not write it but I knew that the signals were coming over the pins :/ \$\endgroup\$
    – epgrape
    Commented Jan 26, 2018 at 9:43
  • \$\begingroup\$ @epgrape OK dude. The foil was an attempt not to stop air borne stuff but to increase the capacitance on the interconnects; in effect the same as throwing a bunch of 22pF caps on! The foil would need to be grounded though. \$\endgroup\$
    – Andy aka
    Commented Jan 26, 2018 at 10:01

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