•These remain at the same state during SET and ARMed periods and change only during The presence of the alert tone. Do not replace Die chip yet if any ol these pins do not agree. ■ 'This pin should go high while pressing the ARMed button

Tab/e 4. Logic and voltage chart,

The corresponding alternative values for R3 and R4 are shown in Table 3.

Most of the delay between the introduction of an alert tone and relay activation is introduced by K7 and OG. These may be adjusted to provide a longer or shorter delay.

If one wishes to have both a low level of alert and a high level of alert, this can be done by adding an SPST toggle switch so that pin 5 of U3a (or pin 8 ot U1) can be grounded With pin 5 or pin 8 grounded, only a single tone (852 Hi) will activate the unit With the switch in the closed (grounded) positron, the tone alert can be activated by the digit 7 tor a low-ievel or personal emergency, and in the switch-open position, it will take both tones of the digit 9 to activate the unit.

Weather Watch {Alert) Modifications

Only minor changes are required on this circuit to decode the NWS 1050-Hz alert tone for weather radios that do not have this feature. U1, R3f R5, R1 it C4, C6, and C7 are omitted A jumper is placed between the foils originally intended lor pins 7 and 8 of U1 R14 is adjusted for 1050 Hz at pin 5 or 6 of U2. Activation methods and time vull remain the same.


Sfep One: Most problems with performance can be traced to bad solder joints,

Parts List


R1-10 Ohms, 1 Walt

R12-22k Ohms, % Watt

R13, 14 — 5 kilohms, vertical trimpots


C1t 2, 3—0.1 ^F ceramic disc, 25 V 04,5—0.1 myiar™, 16 V C6+ 6—1.0 electrolytic, 6 V C7, 9—10.0 f-F electrolytic, 6 V C10—3,3 ^F electrolytic 16 V C1t —lOO^F electrolytic. 16 V Semiconductors

D1t 2— 1N34A germanium (or equivalent)

D3— 1N914 silicon (or equivalent)

D5—1N4001 (or equivalent)

Q1 —2N2222 NPN transistor

U3—4001 CMOS logic block

Keep CMOS wrapped in foil until; ready to install LED -jumbo LED of choice solder bridges, incorrect parts placement, or failure to observe polarity ot diodes or capacitors. All construc tion steps should be retraced! with this firmly in mind.

Step Two: Confirm that adequate noise-free audio is actually present at tht> input and that the relay will work out of the circuit-Close the SET switch to activate the relay

Step Three: Use a VTVM or FET-VOM (at least a megohm resistance) and check the voltages listed in Table 4.

S/ep Four: Using a piece of hookup wire, connect one end to ground and carefully touch the other end to both pins 5 and b of U3 with the circuit ARMed. The relay should activate in about tour seconds, if it takes as long as thirty seconds to activate the relay, check R7, R8, C10, and Di It this fails, replace U3.

Step / ive: Check U1 and

U2 for proper tuning.

Step Six Ground pin 8 of U1 and send a DTMF digit 7 signal over the audio input If this activates the relay in 4-6 seconds, then U2 is tuned and functioning, If the relay does not activate, then replace U2 and try again.

Step Seven: Ground pin 8 of U2 and send a DTMF digit 3 signal over the audio input. U this activates the relay in 4-6 seconds, then U1 is tuned and functioning If the relay does not activate, then replace U1 and try again !


1. Rodney A. Kreuter WA3ENK, "Two Meier Tone Alert" 73 Magazine, January, 1979,

2. Stan Horzepa WA1LOUT1 FM/ RPT—Tone Alert Standards/' QST, December, 1979.

3. J, H. Everhart WA3UXH, Toward A More Perfect Touch-

lone Decoder.' 73 Magazine, November, 1976,

4. Rrck Swenton WA1LWV, ■ Tone Decoder Improvements, 73 Magazine, February, 1979.

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