GPS RSSI vs. C/N0 vs. -dBm

WA2ZKDWA2ZKD
in Installation, Antennas and Interference
Here's data I took using the Spectracom GSG-6 Simulator for L1 sats. This compares Kiwi S/N3327 with a SwiftNav Piksi (no antenna, direct connect via DC Block)



Note that the Kiwi has about 15 dB less margin at low levels
M0TAZ

Comments

  • WA2ZKDWA2ZKD
    John has previously stated that the Kiwi GPS was of lower performance, so no surprise. I did that as part of a bigger effort for my day job where I found that its not unusual for well thought of GPS that are 10+ years old have similar lower performance.
  • WA2ZKDWA2ZKD
    While doing this tetsing i noted that very high signal levels caused the kiwi to act odd. Based upon that, I reduced the level applied to to my 3 kiwis here by 3 dB and now do not see the same loss of birds that I was seeing overtime. I feed all my kiwi via a splitter so they all see the same signal, handy for comparisons.
  • G8JNJG8JNJ
    "While doing this tetsing i noted that very high signal levels caused the kiwi to act odd. Based upon that, I reduced the level applied to to my 3 kiwis here by 3 dB and now do not see the same loss of birds that I was seeing overtime. I feed all my kiwi via a splitter so they all see the same signal, handy for comparisons."

    Hmm, I think this is a separate problem to the "GPS fixes diminish" issue.

    It could simply be that some of the stronger signals are overloading the simple GPS receiver when a high gain antenna is used, and this is blocking the reception of weaker signals.

    Regards,

    Martin - G8JNJ
  • WA2ZKDWA2ZKD
    I think the relationship to "diminishing" might have been a coincidence
  • Navnath123Navnath123
    Hi,
    Can anyone explains the relation between RSSI and C/N0, How to show RSSI in C/N0 term.
  • WA2ZKDWA2ZKD
    I cannot
  • G8JNJG8JNJ
    The RSSI value is likely to be derived from the recieved signal strength and may just be an arbitary value. The SNR value is more likely to be directly related to C/No.

    In order to convert it to C/No you need to calibrate the receiver against a known test source, and ideally also know the antenna gain and noise figure of plus distribution gain/loss, so that you can check the results by working backwards from the GPS satellite footprint power density.

    Regards,

    Martin - G8JNJ
  • WA2ZKDWA2ZKD
    I attempted to find the relationship of Kiwi SNR to C/N0 on the Piksi but ran out of time.
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