TX Mute on CDM 625

The handbook for the CDM 625 is here:
https://www.comtechefdata.com/files/manuals/mn-modems-pdf/mn-cdm625_r12.pdf

Your symptom may have something to do with:
5.2.1.3.1.1 CONFIG: Tx  Tx-IF
Tx: Carrier=On (Off,On,RTI) POCO=Off

The RTI (RECEIVE/TRANSMIT INHIBIT) option is supposed to turn off the transmit carrier when the receive side goes unlocked for more than up to 10 seconds (number of seconds selectable).  The transmit carrier should come back up when Rx lock comes back on.  So, it is not clear why you have your symptom.

If the POCO option (Power-On Carrier-Off) option is set to On, then when powered on the modem will have the transmit carrier Off.  You will need to manually start transmission.  This could be your symptom, but you don't say why all your carriers lose receive lock - due all carriers being turned off by the far end?, due to mispointing ? due to power failure at your site ?

Two ideas:

1. Is the receive side of this modem perhaps just being used to monitor its own transmit carrier ?  If so, this would create the symptom you see.  Once it stops transmitting it will permanently have lost receive lock and never start transmitting again.

2. If your "antenna looses comms" was due to power failure at your site and POCO (Power-On Carrier-Off) is enabled, then when the power comes back on the modem will start up with transmit Carrier-Off. This would explain the symptom you see.

Comtech tech support contact phone and email addresses are here:
https://www.comtechefdata.com/contact-us

Best regards, Eric.