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SI RFCI PLI CS L2 C7 V3    L3 RU JI,J2

CS

Tl

S2

SRI

Rl

		VI
	n	RS I
		R3
w		C3
	l ^	i
	1 !	C4
	~ V	LI

Cl    CZ    R4 C6

CII V2 R6 C9 CRI CIO S3

Under-chassit riew of the on«-lub« carrier-cuirent tranaraitter.

Under-chaaais *iew oi the eompanion two-tranaiilor receirer.

vidcs cut-off bias when no signal is being received and rcduces the current drain during thcsc standby pcriods. Collcctor currcnt changcs, due to an increasc in temperaturo, tend to be minimized by the diodę so it prevents relay operation until a very definite signal is received.

A set of test jacks is wired in series with the negative supply vo!tage to the 2N43s collector to measure the current flow for alignment purposes and the rclative strength of the rc-ceived signal. During normal use a short jumper wire is connected to the test jacks to complete the Circuit. The power roquirement for the receiver is nominally 9 to 12 volts. If a 12-volt battery is used. the battery can age and still pmvide maximum reliability. The current drain during standby periods when no signal is being re-ceived is approximate!y 100 microam-peres. When the receiver is installed the current drain is set with the "Sen-sitivity” control for approximately 2 milliamperes upon receipt of the signal.

Consfrucfion

The transmitter is compactly in-stalled in a 7"x5"x2" chassis. A shelf was constructed to run about two-thirds the length of the chassis and the tubę socket. coils. and the rest of the r.f. circuitry is installed on the shelf. The power supply components are mounted in the remaining space. The transformer can be seen to the left in the photo. with the rectifier. filter Circuit. and S_s mounted directly below.

L, is mounted directly below the shelf and Lr is mounted above, next to the r.f. choke and power-line connec-tions. This effectively shields the os-cillator and output circuits from each other and results in very short connec-tions from the output coil secondary to the power-line cord. The r.f. wiring is kept as short as possible by mount-ing C,. Ci. and C_T on their respectivc coils and one single ground tie-point is used for each coil Circuit. The rest of the wiring is straightforward.

The receiver is housed in a smali 5"x3"x2" “Minibox‘*. Ali transistor circuitry was pre-assembled on terminal

Ocłobor. 195?

strips and interconnected with the other components when the strips were mounted. The transistors were wired into place, although transistor sockets can be used if desired. Remembcr to keep a long-nose pliers between the transistor and soldering iron if they are to be wired in. Any layout and straightforward wiring can be used as long as the input coil connections to the power-line cord are short.

Alignment

The transmitter and receiver are aligned and checked after construction with a standard 20.000 ohms-per-\olt v.o.m. Pług the transmitter into the linę. apply power. and let it warm up for a few minutes. Throw S_? to “Car-rier OfT” and insert v.o.m. between the power supply connection on Sr and chassis. The meter should indicate about 130 volts d.c., and the reading will drop to 90 volts when S» is thrown to the “on” side.

Place the voltmeter between grid 1 and ground to check for oscillation. If al) is well the meter will indicate a negative 7 to 10 volts. If no reading, or a very Iow reading. is obtained re-verse cither the primary or secondary connections of Lu If the rest of the wiring is correct the oscillator will operate immediately when Sr is closed. Run the sług of L, about half-way into the coil.

Connect the v.o.m. probes directly across the piąte resistance, R... negative probe to the coil end and positive to the power supply side. Switch the meter-range to read about 10 volts and the meter will indicate the voltage drop across R» produced by the piąte current flow. Adjust the sług of Li for a minimum voltagc reading on the meter. This action will tune L_s to the same frequency as Li and will run about 4 to 5 volts when Li is fully tuned.

The transmitter’s frequency can be roughly determined with a broadcast (Continued on T>age 146)

6A0S

VI

—* Ml- 9UU r. ciec. capaator Cr—10 m/.. HO r, eltc. capucilor Ci—120 mm/- WO r. ditc capalitor Cl. Ci—500 mm/». 600 y. diii capacitor Ci. Cr—m/- 600 Y. diii Capalitor Ci—.0015 m/-. 1000 y₉ diii capalitor RtCi-2.J mhy.. r,/. choke

5#. 5r—S.p.i.i. loggie iwitih Li. Lł-4-2H mhy. TV widlh coil (Stencor WC*tO or equiY.)

Tt—Power tram. 125 y. & 15 ma.; 6.5 r. 0 .6 amp. (Stancor PSH415 or equiY.)

SRi-50 ma. ielenium rectifier

Vi—6AQ5 tubę