MTC-1 Message Transfer Controller
The MTC-1 was designed to "listen" for NWS/NOAA Weather Alert Tones, then activate a transfer switch, turn on a digital pre-recorded message, and
activate a transmitter's PTT switch.
From Left to Right:
The system has a "test" mode to setup levels between the receiver(s), the transmitter's audio input, and the PTT sense level.
The Trigger Level monitor indicates received audio levels so that the Tone Decoders do not overload.
The receive Alert Status shows if "BOTH" EAS tones are received together (853 and 960 Hz for commercial broadcast radio) on LEDs "Pri 1 and Pri 2". The secondary
(alert) tone is at 1050 Hz for NWS/NOAA VHF broadcast. The tones must be detected by the appropriate tone decoders (frequency selective switches) for the system to
automatically activate. When that occurs, the red LED will illuminate to confirm the process. This event combination (series-of-three) removes the chance of false
triggering. This is a little like the PL tones used in 2-way communications.
The Send Message Status lights indicate when the pre-recorded message and PTT are active. Note that they can be turned off for testing or other standby purposes.
The rest of the controls serve audio functions; Input Drive level, status indicator of empty carrier or carrier with data (voice), monitor levels for broadcast (source) audio
and recorded message audio (for balance of the monitoring and re-transmit functions). There is also a reference LED VU meter on the common audio bus and an
internal/external speaker monitor.
Connections are fairly self explanatory; the system is designed to run on mains power with a 12 to 18 volt power backup. The interface to the transmitter is via RCA jacks
and must enter the transceiver through a customized, or modified, mic cable. The Remote Monitor provides Line Level or Speaker outputs. The line output can be used
for "Air Checks" via a DAC/DAR or other device, if desired. The Audio Loop can be used for any audio conditioning device (equalizer, compressor, limiter) and is
normally shorted with a (tethered) jumper. A remote ENDEC (encoder/decoder) may be used to trigger the system and the internal switches may be accessed for remote
use as well ... like flashing a warning light in the control room or triggering a recorder, timer, or ancillary transmitter. Audio input is high dynamic range and will handle
line levels up to about +18 dBm.
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The purpose of this project was to alert local Hams in our club's area that the National Weather Service (NWS) has issued some form of Alert, Warning, Watch, Advisory
or other message such as Amber Alerts. Most people do not continuously monitor NWS Weather Receivers, so this system takes another route; In our area, our club
members, and the members of surrounding areas generally use a common FM Simplex frequency on 2-meters. This is most often the de facto calling, chatting and
talk-in channel. We keep 146.52 open since it is the designated (band plan) calling frequency and have standardized on 146.58 as our primary and 146.55 as the
This system has not yet been put into service because we are researching the proper format to legally run an automated simplex message system. It looks like we'll also
need to detect if audio is present on the simplex channel, to avoid accidental interference to a QSO in progress. This will be accomplished with a simple audio detector
switch and a repeat timer ... if the frequency is in use, the controller will store and hold the message and try again in some specified time, say, 1 minute. It will continue to
try to send until the channel is open and the message is completed successfully.
The message will be something like this: "N1KPR / WX ... Weather Alert Message Received." Once we have established the legalities, I will insert the club's callsign in
place of mine.
Left and right side of controller.