Bob's Blog #12: Long Tone Zero (LiTZ)

S-COM’s 6K, 7K, and 7330 support a feature known as Long Tone Zero, or LiTZ. If you’re not familiar with it, read on!

LiTZ is a system for requesting aid during an emergency. It’s simple: Transmit a DTMF “0” character for at least 3 seconds and then announce your emergency. Nearly all modern mobiles and handhelds have DTMF keypads, so no additional hardware is needed by the user.

In areas without repeaters, transmissions are made on simplex frequencies set aside for the purpose. Of course, the transmitting station must be within range of a monitoring station that’s either manned or equipped with a LiTZ alarm that can alert a volunteer.

(There’s another emergency system called The Wilderness Protocol. It asks volunteers to monitor standard simplex channels, particularly 146.52 MHz, for 5 minutes beginning at the top of each hour, or at least every three hours starting at 7:00 AM local. It’s sometimes combined with the LiTZ protocol.)

Naturally, having a repeater blanketing the affected area is better than simplex: The coverage is greater, and the repeater frequency becomes a well-known gathering place that’s more likely to be monitored.

If the repeater area is busy with tourists and visitors, and its frequency isn’t well known, it may help to add a receiver dedicated to the local emergency channel (or the national calling frequency of 146.52 MHz) via a spare port on the controller.

If the repeater is in a sparsely-populated area, perhaps the controller can bring up a link to an off-site system where the announcement is more likely to be heard.

In any case, having a repeater in the served area may eliminate the need for each monitoring station to build or buy a LiTZ decoder box. That’s because the repeater controller can detect LiTZ transmissions and then alert volunteers via some other method.

For example, it may be possible to acquire surplus paging receivers and program the controller to send the appropriate tone page. (For the 7330, the choices are single-tone, dual-tone, two-tone sequential, 5/6-tone, DTMF, SELCAL, and Plectron.)

Another possibility is to have a LiTZ transmission prompt the controller into encoding a different CTCSS tone that activates volunteers’ radios.

To attract attention after the volunteer radios are unsquelched, the controller can generate a stored-speech announcement, a loud siren or stutter tone, some musical notes, etc.

It follows that if Long Tone Zero is a good idea, then Long Tones 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, *, and # should be useful too, right?


All three controller models can trigger a separate macro for each long tone character. They can be used for non-emergency actions; for example, Long Tone One places the repeater in carrier access mode while Long Tone Two puts it in AND-CTCSS mode. Long Tone Star links two ports together and Long Tone Pound unlinks them.

Additionally, the 7330 lets you assign three independent sets of long tone macros – one set for each receiver.

How does it work? There’s a timer on the DTMF decoder that checks incoming characters. If a character exceeds a certain duration, its associated macro is executed. For the 6K and 7K, the timer is fixed at 3 seconds. For the 7330, the timer is programmable.

Long tone decoding works regardless of whether DTMF muting is ON or OFF (but listeners won’t hear the long tone if DTMF muting is ON).

Compared to using macros, long tones have these attributes:

            • A single digit is easy to remember
            • A long tone won’t “false” on human voice

See page 7-29 in the 7330 manual for commands associated with LiTZ.

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