Midland GXT720 Instructions

Transmitter alignment method

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TRANSMITTER ALIGNMENT METHOD

1. Frequency Setting

A. Connect a frequency counter or communications service monitor capable of at

least five watt RF.

B. Press the PTT switch.

C. Adjust CT201 trimmer capacitor such that the output frequency is equal to the

channel frequency with a maximum error of +/- 200 Hz. CT201 is located the

right side of VCO Shield can.

2. Output Power Alignment

A. Connect a communications service monitor or a wattmeter and dummy load to

the antenna connector.

B. Press the PTT switch.

C. Adjust air coil (L6) by spreading or de-spreading, to achieve maximum power at

6V Vcc.

Note: Normally, it is not necessary.

D. Adjust semi-resistor(RV1) by rotate, to achieve 0.5W at 6Vcc

3. Deviation Adjustment

A. Connect an audio generator with 10uF coupling capacitor to the microphone jack.

The audio frequency should be set at 1KHz with a level of 200mV.

B. Connect an FM deviation meter or communications service monitor to the

antenna connector. Set the monitor to read peak deviation.

C. Press the PTT switch.

D. Adjust RV2 for +/- 2.0KHz deviation. RV2 is located the bottom right side of PCB.

GXT720/775

Table of Contents

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Page 1 TRANSMITTER ALIGNMENT METHOD GXT720/775 1. Frequency Setting A. Connect a frequency counter or communications service monitor capable of at least five watt RF. B. Press the PTT switch. C. Adjust CT201 trimmer capacitor such that the output frequency is equal to the channel frequency with a maximum error of +/- 200 Hz.
Page 2 LABORATORY TESTING PROCEDURES GXT720/775 UNIT TEST - (UNIT ASSEMBLED) TEST PREPARATION 1) Install Alkaline battery (observe polarity markings). 2) Turn on unit by pressing the power button. SYSTEM TEST 1) Radiated Transmit and Receive performance may be observed. 2) Audio out & Audio in are available at the Headset jack.
Page 3 LABORATORY TESTING PROCEDURES GXT720/775 SPECIFIC TEST METHODS AND GUIDANCE Modulation Characteristics – (paragraph 2.1047(a) of the Rules) FOR TX AUDIO FILTER RESPONSE 1. Connect audio generator with 10uF coupling capacitor to microphone input jack. Press PTT button. 2. Connect RF output with modulation meter. (Filters of modulation meter should be set to a 25Hz to 15KHz.)

Gxt775