EFJohnson 7780 service manual Receiver Performance Tests

ALIGNMENT PROCEDURE AND PERFORMANCE TESTS

PERFORMANCE TESTS

6.8 RECEIVER PERFORMANCE TESTS

6.8.1 PRELIMINARY SETUP

This transceiver does not have a special test mode that can be selected to perform testing. Therefore, temporary conventional channels are programmed to perform this function. Program channels near the low, middle, and high ends of the band (wideband, narrow band or both) and with and without Call Guard (CTCSS/DCS) squelch as applicable. In addition, to check high and low power and talk-around operation, program High/Low Power and Repeater Talk-Around option switches. Proceed as follows to check receiver operation:

1.Select the channel near the center of the band (around 860 MHz).

2.Connect the signal generator to the antenna jack (see Section 6.1.2 for more information). Set the output to the channel frequency, modulated with 1 kHz at 3 kHz (wideband channels) or 1.5 kHz deviation (narrow band channels).

6.8.2 SINAD SENSITIVITY

NOTE: The audio output level of the accessory con- nector is at a lower level than at the internal speaker. In addition, the internal speaker automatically mutes when a load of approximately 1k ohm or less is con- nected to this output.

1.Connect a SINAD meter to the speaker output of the RPI (see Section 6.1.2).

2.Decrease the signal generator output to obtain a 12 dB reading on the SINAD meter. The signal gener- ator output should be 0.35 µ V maximum. If required, temporarily readjust squelch for “0” as described in Section 6.6. (after clicking “Read Tune Settings” to note the current setting).

3.Check both wide and narrow band channels if appli- cable, and also check the channels on each end of the band. Reset the squelch to the previous level if it was changed.

6.8.3 SQUELCH SENSITIVITY

With the test setup used for the preceding test, slowly increase the signal generator output until the squelch just opens (audio is enabled). Then decrease the signal generator output until it just closes. The squelch should open after 12 dB SINAD and close before 6 dB SINAD.

6.8.4 AUDIO POWER AND DISTORTION

CAUTION

Grounding either speaker terminal may damage the audio amplifier. Therefore, make sure that any meter connected across the speaker has floating inputs.

To measure audio output power, the actual level across the speaker must be measured because full output power is not available at the accessory connector. If a load of approximately 1k ohm or less is connected to the speaker output of the accessory connector, it must be disconnected to enable the internal speaker. Proceed as follows:

1.Remove the transceiver cover and connect power as described in Section 6.1.6. Carefully turn the front cover over to access the speaker.

2.Connect an AC voltmeter and distortion meter across the speaker (make sure they have floating inputs). Alternatively, 100 µ F, non-polarized capac- itors can be used in series with the leads.

3.Set the signal generator output for –60 dBm (220 µ V). Minimum audio power should be 0.5 watt across the 16-ohm speaker (2.8 V rms). Distortion should be less than 5% at 0.5 watt.

6.8.5 RECEIVER CURRENT DRAIN

Maximum transceiver current with 0.5-watt audio output is 300 mA. With the receiver squelched, it should be 92 mA maximum.

November 1999
Part No. 001-7780-500	6-6