Setup
- Two nRF9151 SMA DKs (LACA A1), SDK v3.4.1.
- Board B:
mfw-nr+-phy_nrf91x1_2.0.0, running the DECT NR+ PHY Shell sample (samples/dect/dect_phy/dect_shell, unmodified). - Board A: LTE
mfw_nrf91x1_2.0.4, used only as a CW source viaAT%XRFTESTTX test, band 25, around 1890.4 MHz (inside NR+ band 1, channel 1667). - Conducted path: A port → 3 dB → 10 dB or 30 dB → 3 dB → B port, plus short cables.
- Every attenuator and cable was checked individually with a tracking generator and spectrum analyzer (each within 1.5 dB of nominal).
- Board A’s CW output, measured on the spectrum analyzer through the same pads: −9.1 dBm at a −10 dBm setting.
- Board B’s NR+ TX output (
dect rf_tool -m tx, measured as channel power on the analyzer): within ~2 dB of its setting.
Measurement: dect rssi_scan -c 1667 -t 1000 on board B.
| CW level at B’s port (dBm) | RSSI highest / lowest (dBm) |
|---|---|
| ~−75 | −104 / −109 (noise floor) |
| ~−65 | −101 / −106 |
| ~−55 | −95 / −96 |
| ~−45 | −86 |
| ~−25 | −66 |
What we’ve ruled out
- Linearity and repeatability: the reading tracks the input 1 dB per dB over about 40 dB. Swapping the 30 dB pad for 10 dB moved every reading by exactly 20 dB. It repeats within ±1 dB.
- Tone position: placing the tone anywhere from −432 to +368 kHz from the channel centre makes no difference.
- Leakage and saturation: opening the link gives noise only, and no saturations are reported.
Questions
- How is the RSSI in
dect rssi_scandefined? Is it total power in the 1.728 MHz channel, per subcarrier, or something else? Is it referenced to the antenna port? - Is a ~40 dB under-read expected for a narrowband (CW) signal? Does a real NR+ (OFDM) signal read correctly?
- Does the expected-RSSI / RX gain setting affect the reported value?
