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CC1101: Load capacitance causing frequency offset?

Oscar Walsh
Prodigy 160 points

Part Number: CC1101

Two different products (a 'Controller' and a 'Node') communicate with each other over 915MHz GFSK at 250kbaud, both using CC1101. Comms have been poorer than expected. Checking with a network analyser showed a 50kHz offset between the signals transmitted by the Controller and the Nodes.

I noticed that the 2 CC1101 circuits use different brand crystals (both 26MHz), with different balancing capacitors. I changed the xtal and caps on one of the Node PCBs to match the Controller PCB, and the offset for that Node didn't reduced to 20kHz.

My questions are:

1. Is this frequency offset normal/OK? Is it ok to just compensate with the frequency compensation register?
2. Is the crystal/caps wrong on one or both of these designs?

Controller schematic (xtal: CG01972-26M):

image.png

 

Node Schematic (xtal: ABM8G-26.000MHZ-18-D2Y-T):

image.png

 

Any feedback would be much appreciated.