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Packet transmission - oscilloscope on antenna

Arthur Sadler
Intellectual 280 points
Other Parts Discussed in Thread: CC1120

I'm sending fixed sized 20 byte packets, one packet per second @ 50ksps with a CC1120.

I imagined the packet would be seen as a 7.something ms long excitation blip on the aerial, but when looking at the aerial with a scope I can see appprox 470us blips of activity, mostly 40ms apart.

Is this expected? Thanks.

  • 0
    TI__Guru**** 317180 points
    Sending a 20 byte packet with standard preamble + sync will take 1/50e3*8*(4+4+1+20+1)= 5 ms.

    A scope on the antenna connector is generally not a good way to do measurements due to bandwidth of the scope. Please post a screenshot from the scope.

    What is your objective with the measurement?
  • 0 in reply to TER
    Intellectual 280 points
    Hi,
    My objective was just to see how long the transmission was out of curiosity, as I had been having trouble getting fixed length packets working (seems solved now).

    Looking at the scope this morning I can see nothing at all on the aerial, so I think what I was seeing yesterday was actually just ground lift caused by USB comms to a PC.

    Thanks.
  • 0 in reply to Arthur Sadler
    TI__Guru**** 317180 points
    A better way to measure this is to take PKT_SYNC_RXTX out on a pin and measure the length of this pulse.