CDM1250 receive issue after adding MDC ID on TX

[kc2kvy]

So at the request of the local fire chief and my boss, I added in transmit IDs on the fire trucks and ambulances as well as the portables. All has gone well, except on the two ambulance's CDM1250s. Upon releasing the PTT, if the dispatcher answers the unit immediately, no audio comes across although the red blinking "receiving" LED lights up and the display shows that the unit is receiving - almost as if the transmission does not have the correct PL tone. If the transmission continues long enough, the audio will cut in.

I've recorded a short video of the issue and posted it: http://www.youtube.com/watch?v=ncqYKmM0IiE. The first transmission has about a five second pause before the dispatcher answers, and that comes through clearly, but they answer quickly after the second transmission, and that one is muted.

Whatcha think?

[kb4mdz]

Maybe you've checked MDC necessary for RX, also?

[kc2kvy]

I have, because I've programmed the aliases for each unit on the system. This was one if the reasons for enabling MDC- allowing the mobile units to identify the transmitting unit.

[AEC]

It appears your issues is with MDC MUTE timing.
Look at the UNMUTE timing, it is probably programmed for longer duration than necessary. Most times, 325mS is adequate to eliminate the MDC data burst on RX unsquelch, but your settings may be programmed for more time than required to eliminate the noise.

DOS, or Data Operated Squelch, Unmuting the valid signals AFTER the MDC data burst has been transmitted and received and the receiver returns to normal operation once the MDC data has ended, a bit like PL/DPL turn off codes to eliminate the squelch bursts heard so often, DOS performs the same task.

[kc2kvy]

It appears your issues is with MDC MUTE timing.
Look at the UNMUTE timing, it is probably programmed for longer duration than necessary. Most times, 325mS is adequate to eliminate the MDC data burst on RX unsquelch, but your settings may be programmed for more time than required to eliminate the noise.

DOS, or Data Operated Squelch, Unmuting the valid signals AFTER the MDC data burst has been transmitted and received and the receiver returns to normal operation once the MDC data has ended, a bit like PL/DPL turn off codes to eliminate the squelch bursts heard so often, DOS performs the same task.

You were absolutely right. I'm not sure why it didn't occur to me to check this earlier - the DOS was set to 500ms! Thank you so much for the help.