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RSSI "holes" with CC1100

Bernhard Firner
Prodigy 30 points
Other Parts Discussed in Thread: CC1101, CC1100

Hi,

We've been taking some histograms of the RSSI values recorded by the CC1100 and we've noticed that there are some values that do not occur as often as they should. We have our transmitter on a moving platform that makes it sweep through different RSSI ranges but when we look at the RSSI frequencies in a histogram there are some "holes" around -51 and -57 dB where RSSI values do not occur. Has anyone else seen this and identified the problem? Does this occur in the CC1101?

It's not that these values never occur, just that they appear to be unrealistically rare. We summed the histograms from several trials and obtained the one below (with 1dB bins)

 

  • 0
    TI__Mastermind 18780 points

    This was new to me, what are your AGCCTRL settings and other register settings like datarate, rx filter bandwidth etc? You say you monitor RSSI, is the chip set to serial or packet mode? What kind of signal do you monitor? What is a valid RSSI reading in your application?

     

    Charlie

  • 0 in reply to CHS
    Prodigy 30 points

    Thanks for responding, maybe you can see a problem with one of our AGCCTRL registers or something else.

    We are operating at 902.1 MHz using MSK with a datarate of about 250Kbps and a rx filter bandwidth of 541kHz. We are using 4 bytes of preamble and 4 bytes of sync word. We read RSSI on a per-packet basis by waiting for GDO0 to go high and then low to indicate that a packet was received and then read the RSSI value from the two status bytes appended to the packet by the CC1100.

    Our AGCCTRL registers are set to:

    AGCCTRL2: 0xC7

    AGCCTRL1: 0x00

    AGCCTRL0: 0xB2

     

    We have been using the radio for localization and tracking so any RSSI value is valid. We first noticed this when we were looking at a plot of RSSI values as someone walked away from the receiver with a transmitter and saw that there were odd jumps in RSSI where the value never went. When we put the data points into a histogram we saw RSSI holes. I have also plotted all of our historical data in histograms and we see the same thing.

     

    -Ben