American listeners might not be used to the Israeli Elbit Systems "Tadiran" communication system being used by the Mexican military. The Navy, in particular, is making full use of its many capabilities.
This strong signal (notice full noise quieting) on 4820 kHz is probably from Baja California. We see here several elements of the system: (1) The 1000-Hz tuning/sync beep which preceeds all transmissions; (2) The proprietary 4FSK Autocall system's tones centered at 2850 Hz, serving a variety of linking and communication functions; and (3) the integrated data comm capability, in this case using MIL-STD-110A.
The multiple callups before every 110A burst likely indicate that full encryption is in use. Voice and clear 110A have been heard at times, including one "Radiograma" heading which confirms that the Armada de Mexico (Mexican Navy) is the source.
Below we see the Tadiran voice security system in use by the Mexican Navy on 4885 kHz. The different noise levels indicate that we have an exchange between two stations. Again, we start with the 1k beep and the four FSK tones. The payload, however, is in a scrambling system looking and sounding a bit like Vocoder. It is definitely significant that the top two tones run continuously during the secure voice. This could mean several things, but it would be guessing to say for sure.
Plots made with Gram.exe and Spectrum Lab.