Author Topic: Real Time Modes, Timing Issues  (Read 7207 times)

VK3OE

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Real Time Modes, Timing Issues
« on: 2011-04-27, 13:06:41 »
Hello,

I am running a RCC-1258MkII control and Radio unit over a 3G network. Settings are; Jitter Buffer 5, Jitter Delay 3, Audio Packet Size 40ms, Audio quality 1. This works fine most of the time for classic audio with some drop outs, but the unit seems to be able recover from a poor connection, it never locks up and I never have to reset anything.

I also run a chirp radar and use the remote site as the receiver. The chirp is a continuous signal of 500Hz to 2500Hz repeated every 1 second. In the chirp receiver (implemented in Spectrum Lab)  the timing of the received signal is very evident as a change in delay of the signal will cause the received chirp to jump in time causing a shift in the received signal. For some reason the system often gets itself very tied up with many time jumps and truncated chirps (especially for tone type signals), so that if I stop the chirp transmission I hear bits of the received chirp ( but not complete chirps) for several seconds after the transmission is stopped. If I start transmitting a chirp again the system still has the same problem. The only way to recover from this situation is to reset the Radio unit, reseting any of the other components in the system will not overcome the lockup problem. Thus, it seems that the radio RCC unit does not handle such realtime signals very well, the time jumps and signal truncation are very evident and recovery from this situation is difficult.

Is it possible to modify the way in which the packet buffering occurs so that for real time signals if there is a packet loss then it is not buffered at all but the time base is kept. There is clearly some issue with tone signals when compared to voice.

best 73,
Andrew
VK3OE