Trouble Shooting Guide

Axxcelera Broadband
Troubleshooting-Installing an RF link - 23 - Issue: 5.3.x
Rev 2
8 Modem RSSI
RSSI is the Receiver Signal Strength Indicator for an SU, and is displayed in dBm. RSSI is not available
on an AP, because all SUs transmit so that there signal is received at the AP in the range of -71 to -78. The
RSSI is displayed by the “hmm modem rssi” command, but is also displayed by the “hmm link status” and
“hmm modem txpower” commands.
SU Modem RSSI
192.168.3.254 hmm> modem rssi
mean actual RX chain attenuation +35.375 dB demod gain stage OUT
actual RX gain +80.100 dB
baseband gain +6.000 dB
RSSI -50.725 dBm Strong signal
Of the four numbers reported by the “hmm modem rssi” command, only one - the “RSSI” – is of any real
value for debugging RF problems.
8.1.1 mean actual RX chain attenuation
The amount of attenuation placed in the receive path, to prevent the receiver from being overloaded. When
the SU is receiving no signal, it has maximum receiver gain, so the mean actual RX chain attenuation
would be 0dB. (The RSSI would typically be –85dBm when no signal is received).
8.1.2 actual RX gain
This is the total amount of RX gain in the radio. This is deduced from the calibration data for each radio.
This number is of no practical use.
8.1.3 baseband gain
This is the total amount of baseband gain in the radio. This is a constant, and is of no practical use.
8.1.4 RSSI
Receiver Signal Strength Indicator displayed in dBm. It is followed by an indicator to tell you if the signal
strength is acceptable. The RSSI is calculated by adding the total gain and subtracting it from the
attenuation:-
RSSI = mean actual RX chain attenuation - (actual RX gain + baseband gain)