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CC1101 spurious emissions from modulation test

Stephen Phillips1
Expert 1250 points

Other Parts Discussed in Thread: SIMPLICITI, CC1101

We are operating this thing at 904.15mhz infinite packet length with random data.

The simpliciTI settings1651.smartrf_CC1101_01.h

chan spacing 116khz
data rate 250kbps
modulation GFSK
base frequency 904.15mhz
lower RX current
RX BW 540khz
deviation 127khz
Xtal 26mhz

And an image of what spurred this post (bad pun intended)

The yellow (old yellow) is max old (I mean max HOLD) cyan (teal?) is trace average and the magenta trace is min hold

So ... is this FCC (15.249)  passable? please give some tips about what we are seeing.

  • 0
    Expert 1670 points

    What is your output power? I think the highest output that will pass is around -1dB. I would recommend going for FCC 15.247 instead of 15.249. Refer to SWRA123B: CC11xx Settings for FCC 15.247 Solutions. Under 15.247, you can use the highest output powers of the chip.

    First, I would suggest trying 2-FSK instead of GFSK and 165Khz deviation and see if those go away (it's the easiest / cheapest thing to try...). Those are the settings recommended on Pg. 5 of SWRA123B: CC11xx Settings for FCC 15.247 Solutions. I'm not sure if the wider bandwidth will qualify for 15.249.

    Which chip are you using, and why type of balun and antenna? If using any inductors, I would recommend trying wirewound inductors instead of multilayer inductors. I had some problems passing FCC harmonics until I switched over to wirewound.

    -Chad C.

  • 0 in reply to Chad Christensen
    Expert 1250 points

    Output power directly coupled is roughly -1.7db

    Part is CC1101  the balun circuit is the same discrete version as on the CC1101EMK network with saw filter attached, antenna is PCB trace with impedance match.

     Inductors on this board are 0402  Johansen L-07. The Q is 20 to 30 at 900MHz   and SRF is 2.9 GHz for 18 nH part  http://www.johansontechnology.com/images/stories/rf-inductors/cci/jti-cat-rf-ind.pdf

    http://www.digikey.com/product-detail/en/L-07C18NJV6T/712-1409-2-ND/1840069

    Next version has wire-wound inductors as the others are hard to get from Digi-Key now. I’m sure we would comply with 15.247 I was just wondering about 15.249 with these I was just wondering about this modulation artifact or whatever it is. Thanks for the reply.
    Let me know if this helps those thinking (pondering) this question (anything to have a useful thought).


    Stephen