EFJohnson 761X UHF Adjustments, PLL Adjustment UHF Models, Transmitter Adjustments UHF Models

ADJUSTMENT PROCEDURE

UHF ADJUSTMENTS

NOTE: Perform the preliminary setup described in Section 6.2 before proceeding with these adjustments.

6.6 PLL ADJUSTMENT (UHF MODELS)

1.Remove the bottom cover by removing four screws. Connect a DC voltmeter to check point CP1 shown in Figure 6-6.

2.Select the channel at the low end of the band

(Test Ch. 1). This is done by pressing the ↑ ↓ arrow

keys to highlight “Memory CH” and then pressing the adjust keys (←/→, PgUp/PgDn, or spacebar/

backspace) to select the channel.

3.In the receive mode, the meter reading should be 1.5 volts. If this voltage is significantly different, adjust L23 (it may be necessary to remove the shield).

4.Key the transmitter using the switch on the test cable and the meter reading also should be 1.5 volts. If this voltage is significantly different, adjust L26.

5.Unkey the transmitter and select the channel on the high end of the band (Test Ch. 2). The meter reading in the receive and transmit modes should be 3.5 – 5.5 volts. Replace the bottom cover.

6.7TRANSMITTER ADJUSTMENTS (UHF MODELS)

6.7.1 REFERENCE FREQUENCY

1.Select the low power channel on the high end of the band (Test Ch. 2).

2.Scroll down to “TXF SET” on the screen and press (Enter). Monitor the transmit signal with a fre- quency counter and key the transmitter using the test cable switch.

3.Adjust for the displayed frequency by pressing the computer adjust keys. Unkey the transmitter.

4.Press (Enter) again to select the second adjust chan- nel. Key the transmitter and adjust for the displayed

frequency. Unkey the transmitter and press (Enter) again to exit this function.

6.7.2 OUTPUT POWER ADJUST

1.Select the high power channel at the low end of the band (Test Ch. 3). Connect a power meter to the antenna jack.

2.Scroll to “Power (Hi)” on the screen and key the transmitter using the test cable switch. Use the com- puter adjust keys to set the following power. Unkey the transmitter. Repeat for the Low2 (Test Ch. 4) and Low1 (Test Ch. 5) power levels.

High Power = 35 watts

Low2 Power = 20 watts

Low1 Power = 3.5 watts

6.7.3 FM DEVIATION ADJUST

1.Connect an audio generator to the microphone audio input of the test cable (pin 5 shown in Figure 6-3). Set the generator output for 1 kHz at 40 mV rms.

2.Select the low power channel at the low end of the band (Test Ch. 1). On the computer screen, scroll to “MOD N” if setting narrow band deviation or “MOD W” if setting wideband deviation.

3.Monitor the transmit deviation with a communica- tions monitor set as follows: HPF = Off, LPF = 20 kHz, De-Emphasis = Off, Detector = (P–P)/2.

4.Key the transmitter using the test cable switch and

set the following maximum deviation by pressing the adjust keys (←/→, PgUp/PgDn, or spacebar/ backspace). Unkey the transmitter.

Wideband (30 kHz) Models - 4.2 kHz Narrow Band (12.5 kHz) Models - 2.1 kHz

5.If the transceiver operates on both narrow and wide band channels, select Test Ch. 6 and also adjust the deviation on that channel (see note in Table 6-2).

November 1998
Part No. 001-7600-001	6-8