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[Linrad] Re: SDR-IQ Birdies - the Solution


You might want to try replacing ferrite beads FB4 and FB6 on the DB-9
connector with shorts (solder blobs). We have identified this as a
potential source of EMI. The beads on the USB connector should already
be 0 Ohm resistors. Some of the bare boards that were shipped without
enclosures might still have beads in locations FB1 and FB3. These can
also be replaced with shorts.



On Oct 16, 11:23 pm, VK2KU <vk...@xxxxxxxxxxxxxxxx> wrote:
> Well, well, well - we learn new things every day!
> The lid of the SDR-IQ is NOT electrically connected to the body of the
> box.
> Fortunately the circuit board and various cable connections ARE
> grounded to the body of the box.
> The lid is held in place with 8 small countersunk screws - M2.5?
> The lid has been carefully painted, including the bevelled edges of
> the screw holes,
> thus preventing the screws from making electrical contact with the
> lid.
> The lid itself and the box are of course separated by 2 layers of
> paint.
> Just to make quite sure that no electrical connection occurs,
> the screws themselves are also black anodized - another insulating
> coating.
> I removed the paint from the countersunk holes with a hand-held 90-
> degree counterbore bit.
> Then, lacking any other suitable screws or a more suitable tool,
> I spent a happy and fiddly half-hour using a small flat file to remove
> the anodizing from
> the underside of the 8 screw-heads. I also lightly touched up the
> threads to show some metal.
> The result was the almost complete elimination of the offending
> birdies - 99% anyway.
> A bit of aluminium foil as suggested by Leif completely eliminated the
> last traces.
> Every SDR-IQ owner needs to do this!
> 73  Guy  VK2KU

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