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> Pcb Layout Of Cc1200 Critical Points
Posted: October 19, 2016 07:48 am
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Hello everyone,

I'm using CC1200 for testing purposes from several months and now is time to design a pcb to fit my needs. The starting design I used is the CC120xEM 420-470MHz Rev 1.1 board. Here is the datesheet: http://www.kynix.com/uploadfiles/pdf8827/CC1200RHBR.pdf

In my own design I just changed the SMA connector with an U.FL (hirose U.FL-R-SMT-1). I kept the same BOM as the original design. Unfortunately the resulting PCB manifactured and assembled with components is not working: I can 'talk' with the CC1200 (but this was the easy task) but as long as I can see no data is received or transmitted.

Using SmartRF Studio and stacking my own board onto a TrxEB board I made the following tests (using an original TI CC120xEM 420-470MHz board as a counterpart):

1) using PacketTX mode (default configuration) I'm not able to transmit a single packet on the other side;

2) using PacketRX mode (default configuration) I'm not able to receive a single packet from the other side;

3) using ContinousRX mode I can clearly see the RSSI signal level grow up of 60/70 dB;

4) while in TX (using a Spectrum Analayzer) I can clearly see the proper signal (centered on 433.9 MHz) level-up to the same values I typically see when using the original CC120xEM boards.

all tests have been made using "Generic 434Mhz -> Symbol rate 1.2Kbps , 2FSK, 12.5 kHz, Channel Spacing (434Mhz)" pre built configuration with units placed about 1-2mt far.

I cannot undestand why data are not 'coming' in (or out).

Excluding design faliures my doubts are about the pcb manifacturing and/or assembly but of course I'm open to any other advice/suggestion.

Supposing an assembly issue my final questions are:

What are critical components into RF signal integrity ?

How can I check if the RF signal is 'correctly' received/transmitted ?

Best Regards,
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Posted: October 19, 2016 10:10 am
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If a test rig made from the OEM parts (not on a pcb) works then obviously the pcb is the fault. I strongly doubt whether changing the RF connector is the fault unless it's pinout is different (or it's impedance) and you're shorting the output to ground.

Checks to establish tx/rx paths revolve around terminating the antenna ports on both the tx and rx with fixed impedances (eliminating the antennas) and testing for radiative and received power levels. On the receive side you'd do this with the appropriate signal generator.

Can you get hold of a DSO and check the bit pattern of the received signal after the receiver front-end? to visually check the protocol?

May contain nuts
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