4Mbps hack wiring & 48 MHz spurs

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Sylvain Munaut 246tnt at gmail.com
Thu Nov 1 20:34:44 UTC 2012


Just fyi, here's how I did the 4msps wiring hack :

http://i.imgur.com/TODkU.png

Basically use resistors (I used 270R which is a bit high ,between 20 and
10R would bwe better) on the back side on the PCB.

I initially started with wire jumpers on the pins, then moved to resisors
on the top but that created a huge loop area with the ground return (there
is no gnd on those connection) which was heavily radiating.

Mounting on the back like that dropped it significantely for me (especially
on baseband), but you still clearly see it.

I think the FPGA drive strength on the data pins is still way too high and
should be reduced.

Maybe using spread spectrum on the MCI would be another idea ?

Cheers,

    Sylvain
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