Quik Call I

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title=Quik Call I
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Quik-Call I, also known as 2+2, is a selective calling method originally used in one-way paging receivers. In US fire service use, the tones are sometimes referred to as ringdown tones. [Ringdowns in modern fire dispatch systems usually have two redundant communications paths that may include two-way radio, microwave radio, telephone, or data service links.] The "Quik-Call" name is a trademark of Motorola. A Quik-Call format call sends a pair of tones followed by 50 to 1,000 milliseconds of silence and then a second pair of tones. Decoders look for a valid first tone pair followed by a valid second tone pair within a defined length of time, (a "time window"). For example, a decoder detecting a valid first tone pair might allow up to 4 seconds for a valid second tone pair to be decoded. If no valid second tone is decoded within 4 seconds, the decoder resets and waits for another valid first tone pair. The system is less susceptible to falsing because it employs pairs of tone decoders that must detect valid tone pairs simultaneously.

The name is easily confused with Quik-Call II, Motorola's name for two-tone sequential or "1+1" signaling.

Typical uses

Quik-Call I is most famous for use in the fire service. The 1970s television show, "Emergency!", depicted its use for base station ringdowns in the Los Angeles County Fire Department. Many users employed Quik-Call I to ring down or alert mobile radios with decoder options built into them. In Motorola mobile equipment, the decoders were often housed in a box that bolted on to the radio control head. In the 1960s, it was also used to actuate tube-type Motorola L03-series receivers used to call out volunteer firefighters or (in the same type of receivers) for a contact closure to trigger sirens used to call out volunteers.

Quik-Call I is almost identical to ICAO's SelCal used to ring down airborne aircraft on HF single-sideband systems over trans-oceanic routes. Each aircraft equipped with the system is permanently assigned a four-letter code unique to that airframe. At the beginning of a trans-oceanic flight, the pilots and controller test the system (the controller sends the aircraft a SelCal call to check it's operation). Thereafter the controller rings down the aircraft if instructions needed to be given. The system is one-way, only allowing the controller to signal the aircraft, not vice-versa.

Code (tone) plans

Quik-Call I systems had three, pre-defined tone plans. These were referred to as "Z", "A", and "B". These tone plans ensured a reduced probability of falsing by spacing tones within each plan far enough apart in frequency that a decoder could tell the discrete tones apart. If all tones in a system were from a single plan, there should be no falsing in a system with good level discipline.

Each tone within a plan was assigned a letter. For example, tone "KZ" was 716.1 Hz. Code plans described individual calls by the letters of the four tones. For example, a decoder may be set to decode DJNP, (the tone pair DJ followed by the tone pair NP). This was sometimes written DJNP, DJ+NP, or with the tone plan letter, DZ JZ+NZ PZ.

Some systems were used with group call plans where a two-tone sequence (Quik-Call II equivalent) would ring down all decoders that were configured on a specific group call. In the above example, group calls were always noted as the middle two letters. JZ+NZ would call all radios with code JZ as the second code of the first tone pair and NZ as the first code of the second pair. For example, FZ JZ+NZ CZ would also be alerted by the group call tones JZ+NZ.

In California, the "Z" tone plan was most common. The California Department of Forestry used the "Z" plan before it was replaced by DTMF. County of San Diego and the ICAO SelCal system used tones from the "Z" plan.

How it is used in a system

Radios with Quik-Call I decoders may monitor all system traffic or remain muted until called, depending on the system design. When the radio receives the correct tone pairs in the proper sequence, it may momentarily buzz or sound a Sonalert. An indicator light may turn on and remain latched on. In most systems, the radio's receive audio would latch on if normally muted.

In the "Emergency!" television show, the SCU decoder (Station Control Unit) turned on the lighting, momentarily activated a Federal Signal Vibratone horn klaxon, turned on the overhead loudspeakers, and probably [Motorola, "Specification Sheet: Fire/Ems Station Alerting Solution with Hardware CEB Aux I-O", [http://www.motorola.com/governmentandenterprise/contentdir/en_US/Files/SolutionInformation/fire_alerting_specsheet.pdf R3-11-2012] , 2002:1] turned off cooking appliances.

Maintenance issues

Encoders had a complicated level adjustment process designed to compensate for equalization to produce acceptably flat tone levels on the transmitted signal. The problem is similar to DTMF: simultaneous tones of a tone pair must be similar in level so the decoder can detect the presence of both tones.

On FM two-way radios, tone pairs are usually sent at a level that equals two-thirds of system deviation or less. For example, in a +/-5 kHz deviation system, the tone encoder is set to produce 3.3 kHz of transmitter deviation, (modulation,) or less for every tone pair. Keeping the tone modulation below 2/3 system maximum preserves the clean sine wave produced by the tone encoder. Sending tone pairs at higher levels causes the transmitter's circuits that are designed to prevent over-modulation to distort or clip the waveform of the tones. Distorted wave forms may not decode properly.

Tone pairs are usually sent at a minimum of 500 milliseconds (ms) to 2 seconds (2,000 ms) in length with a 500 millisecond to 1,500 millisecond silence between tone pairs. Many decoders used in these systems utilized mechanical reeds for decoding. Some required encode times longer than two seconds per tone pair to work with high reliability.

External links

* [http://www.emergencyfans.com/ emergencyfans.com]
* [http://www.clafma.org County of Los Angeles Fire Museum Association]
* [http://www.policeinterceptor.com/emerg.htm Los Angeles County Fire dispatch tone archive]

Notes