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BTD-2 MOD-1272 ADDENDUM
Overview:
MOD-1272 adapts a BTD-2 to mute ANI signaling packets, in particular Motorola’s MDC-1200
packets. It may also work with other signaling protocols that have a known single-tone preamble. In the case of
MDC, there is a preamble of 1800 Hz for approximately 27 msec. MOD-1272 changes the BTD-2 so that it is less
susceptible to falsing on voice as well as eliminating the need to connect the COR input. Another difference is that
the actual decode timing is 1/2 of that programmed. Also, the hardware has been modified to use a crystal for
greater decode accuracy. In all other respects, the product is identical to a BTD-2.
Operation:
Upon detection of a signaling packet, the unit turns on transistor Q5 (PTT hang time out) for
approximately 200 msec. This output can be routed to the squelch circuit of a radio, or be used to clamp the audio
to ground* in order to mute the packet. This is the default configuration. The polarity of the squelch output can be
also be programmed so that the transistor is off during the mute period (set squelch polarity to V+) if the
application requires it.
Only 4 wires of the unit need to be connected: power, ground, RX tone in, and PTT hang time out. The RX level
control pot (R65) should be adjusted as described above. The decode sensitivity will not be as described
however. Expect packet detection to decrease below -14dB SINAD. Note: If you decide to clip the unneeded
wires, be sure not to clip the PROG ENABLE and PROG IN wires.
* Q5 can sink a maximum of 100 mA. Do not exceed or damage will result.
Programming Parameters:
The BTD-2 MOD-1272 comes preprogrammed with the above parameters. If different parameters are needed, the
KL-4F programming interface will be needed. Be certain to use the BTD-2 MOD-1272 programming file. Note that
the actual decode time is 1/2 of that programmed, so that the 0.03 tone detect time above causes the unit to
require a minimum of 15 msec of preamble tone in order to detect a signaling packet.
To increase the sensitivity of the unit, the tone detect time can be set to 0.02, but the risk of falsing on voice is
increased. Conversely, the tone detect time can be set to 0.04 to reduce the chance of falsing, but fewer packets
will be muted.
