Idle channel noise is the signal sent to the network or earpiece in the absence of any speech or other wanted sounds. It is measured for handset and headset configurations by placing handset into a quiet environment (less than 30dBA. Signals are measured and injected into the terminal at the Linear PCM Reference Point (the TETRA CODEC is bypassed).
The maximum noise level at the Linear PCM reference Point under silent conditions shall not exceed -64dBm0p (psophometric weighting according to [G.223, table 4]).
Acoustic echo cancellation shall be operational. It is recommended that the level of single frequency noise components should be 10dB lower than the -64dBm0p figure [P.11].
The maximum (acoustic) noise level at the Ear Reference Point shall not exceed -57dBPa(A) when the value '1' (13 bit linear) is injected into the terminal Linear PCM reference Point with the volume control in the nominal position.
Where there is a volume control the noise level shall not exceed -53dBPa(A) at the maximum setting of the volume control.
It should be noted that the TETRA codec can generate a low level 'burble' when idling. This can prove extremely distracting with headsets and noise gating techniques may be found beneficial.
Copyright ©2002 Andy Fletcher andy@x31.com