EFJohnson 761X, 764X service manual Receiver Adjustments Uhf Models, Uhf Adjustments Cont’D

ADJUSTMENT PROCEDURE

UHF ADJUSTMENTS (CONT’D)

6.8 RECEIVER ADJUSTMENTS (UHF MODELS)

6.8.1 BANDPASS FILTER ADJUST

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

2.Connect an RF signal generator to the antenna jack. Set the output for the channel frequency at a level of 3.2 µV (–97 dBm), modulated with 1 kHz at the following deviation:

Wideband (25 kHz) Models - 3.5 kHz Narrowband (12.5 kHz) Models - 1.75 kHz

3.Adjust the filters automatically or manually as follows:

Automatic Adjustment Method 1

(Adjusts all filters)

a.Select “BPF T1” on the screen and adjust for “0”. Repeat for T2 – T4. Reselect “BPF T1”.

b.Press the F9 key and all filters are automatically adjusted for peak levels.

Automatic Adjustment Method 2 (Adjusts only one filter at a time)

a. Select “BPF T1” and press F8 to automatically adjust it for a peak level.

6.8.2 SQUELCH ADJUST

NOTE: The squelch level can also be set from the front panel as described in Section 3.3.6.

1.Select the channel on the low end of the operating band (Test Ch. 2). channel with LB models and the 150.050 MHz channel with HB models.

2.Connect a SINAD meter with a 4-ohm load to the external speaker jack.

3.Connect an RF signal generator to the antenna jack. Set it to the channel frequency with an output mod- ulated with 1 kHz at the following deviation:

Wideband (30 kHz) Models - 3.5 kHz Narrowband (12.5 kHz) Models - 1.75 kHz

4.Scroll to “SQL” on the computer screen and press the adjust keys to lower the displayed number so that the receiver unsquelches (the 1 kHz tone is heard). Also adjust the volume if necessary.

5.Adjust the signal generator output to obtain 8 dB

SINAD.

6.Press the computer adjust keys to increase the dis- played number to the point where the receiver squelches. Then slowly adjust the number down- ward again until the receiver just unsquelches.

b. Repeat for the other three filters.

Manual Adjustment

a.Connect a SINAD meter with a 4-ohm load to the external speaker jack (see Figure 6-6).

b.Select “BPF T1” and press the adjust keys ( ←/→, PgUp/PgDn, or spacebar/backspace) to obtain minimum distortion.

c.Repeat for the other three filters.

6.8.3 BEEP TONE LEVEL

This adjustment sets the volume of the beep tone that is heard when keys are pressed and at other times (if it is enabled). The computer setup used in the pre- ceding steps is not required for this adjustment. Pro- ceed as follows:

1.Unplug any cable that may be plugged into the microphone jack and locate R60 inside this jack. (see Figure 6-5).

2.Repeatedly press a front panel switch to enable the beep tone and adjust R60 for the desired level.

November 1998
Part No. 001-7600-001	6-10