1-kHz Oscillator Adjustment

TM 11-6625-467-34

Table 3-6. Capacitance Frequency Adjustment

h. Adjust the oscillator frequency reading on the

A N / U S M - 2 6 to 150-Hz by adding or removing

Frequency Shift (Hz)

Capacitance (micromicrofarads)

capacitors from the circuit card. Table 3-4 shows

11.86

1,200 . . . . . . . . . . . . . . . . . . . . . . . . .

the capacitors provided on the circuit card for fre-

2,200 . . . . . . . . . . . . . . . . . . . . . . . . .

23.4

quency adjustment and the amount of adjustment

3,300 . . . . . . . . . . . . . . . . . . . . . . . . .

31.2

each provides, Adding capacitance lowers the fre-

4,700 . . . . . . . . . . . . . . . . . . . . .

37.5

quency; removing capacitance raises the frequency.

i. R e m o v e t h e m o d u l e e x t e n d e r b o a r d a n d

replace the 150-Hz oscillator/counter circuit in the

e. S e t t h e P O W E R S E L E C T O R s w i t c h t o

NORMAL.

card cage.

f Set CIRCUIT SELECTOR switches to 0004.

3-23. 1-kHz Oscillator Adjustment

g. Connect the frequency meter to J3 on the cir-

Perform the following procedures to adjust the

cuit card and adjust L1 for 500 kHz.

l-kHz oscillator:

h. Remove the module extender board and re-

a. Remove the test set from the case.

place the 500-kHz fm oscillator card in the card cage.

b. Using the module extender board, extend the

3-25. 500-kHz Fm Oscillator Deviation

l-kHz/10-kHz oscillator circuit card HU9 above the

Sensitivity Adjustment

card cage.

(fig. 3-28)

c. Connect power to the equipment and set the

Perform the following procedures to adjust the 500-

POWER switch to ON.

d. Pull the shaft of interlock switch S12 to the

kHz fm oscillator deviation sensitivity:

a. Remove the test set from the case.

override position.

b. Using the module extender board, extend 500-

e. S e t t h e P O W E R S E L E C T O R s w i t c h t o

kHz fm oscillator card HV2 above the card cage.

NORMAL.

f. Set the CIRCUIT SELECTOR switches to

c. Connect power to the equipment and set the

5760.

POWER switch to ON.

g. Push the PRESS TO TEST switch and adjust

d. S e t t h e P O W E R S E L E C T O R s w i t c h t o

NORMAL.

the 1KC AMPL control for a reading of 100 percent

e. Pull the shaft of interlock switch S12 to the

on the TEST METER.

override position.

h. Connect the frequency meter to pin 1 of the cir-

cuit card (use module extender board) and read the

f. Construct a low pass filter using a 5-millihenry

output frequency.

inductor and a 560-micromicrofarad capacitor as

i. If the frequency is 1,000 Hz 50, no circuit ad-

shown in figure 3-28.

justment is needed. If the output frequency exceeds

g. Connect the circuit as shown in figure 3-28.

the specified limits, add or remove capacitors from

(Do not connect wires shown by dashed lines).

the collector circuit of transistor Q1. Capacitors C4

h. Set the CIRCUIT SELECTOR switches to

through C8 are normally in the circuit (fig. 3-34). An

2205.

extra pair of connections exist on circuit card HU9

i. Set the audio oscillator frequency to 1,000 Hz

for an additional capacitor (fig. 3-13). Table 3-5

at an amplitude of 1 volt as read on the ME-30A/U

shows the amount of adjustment provided by dif-

(ac voltmeter).

f e r e n t sizes of capacitors. Adding capacitance

j. Leaving the rest of the circuit connected, re-

l o w e r s the frequency; removing capacitance in-

move the ac voltmeter from pin 2 of the 500-kHz fm

creases the frequency.

oscillator circuit card and connect it to the junction

of the inductor and capacitor in the low pass filter as

3-24. 500-kHz Fm Oscillator Frequency

shown by the dashed lines in figure 3-28.

Adjustment

k. Set the RANGE switch on the GR-1142-A to

Perform the following procedures to adjust the 500-

1.5 MC and adjust R2 on the 500-kHz fm oscillator

kHz oscillator frequency.

circuit card for a deviation of 9.5 kHz.

a. Remove the test set from the case.

l. Disconnect the equipment and replace the 500-

b. Using the module extender board, extend 500-

kHz fm oscillator circuit card in the card cage.

kHz fm oscillator circuit card HV2 above the card

3-26. 3.975 MHz Oscillator Detector

cage.

Output Amplitude Adjustment

c. Connect power to the equipment and set the

POWER switch to ON.

Perform the following procedures to adjust the

d. Pull the shaft on interlock switch S12 to the

3.975 MHz oscillator detector output amplitude:

override position.

a. Remove the test set from the case.

3-45