tetra

[dsulistyo]

All, need ur suggestion about case below..

recently our company to apply for tetra trunking communication with personnel in the field. after the application of this technology, found a delay when communicating. whether this delay could be reduced or eliminated?

[Stantheman]

Hi dsulistyo, the delay you are experiencing is what you paid for .. a digital land mobile radio system. The delay is primarily caused by the vocoder processing time (at both ends), along with other digital processes such as A/D, D/A, encryption, the TDMA process, inter-site links etc .. whatever is in the digital processing pipeline between both ends of the overall radio link i.e. radio terminal to radio terminal.

Some of these delays, such as digital backbone links, will exist in an analogue system but the overall delay is much lower and typically not noticeable.

What sort of delay are you getting? Did your organisation set a target for this and sign this off as part of the deliverables? You should be able to measure the delay with a microphone connected to a triggered storage oscilloscope, Tx on one terminal and clap your hands (if the vocoder doesn't handle a clap too well, just try the word "one" or whatever works best), you should be able to capture the original clap and also when it comes out of the receiver of another radio (you shouldn't get any audio howl-round, as you have a nice delay !), then measure the end-to-end delay. Some of the first TETRA systems had up to 1 second of delay, but the latest equipment should be under 500ms .. depends on the complexity of the end-to-end circuit.

All digital radio systems, including TETRA, APCO P25, dPMR, DMR etc .. will exhibit a noticeable audio delay relative to an analogue radio system.

So what you are experiencing is normal and it is not something you can "fix". However for most operational comms it should not be an issue, you will typically only notice it when two radios users are standing next to each other.

BR's, Stan.