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H 520 PLUS

SERVICE MANUAL

Table of Contents

SPECIFICATIONS

1. GENERAL

Channels………………………...……………………………………………………................... 400 Ch AM/ FM 4W

Frequency Range………………………………...…………………………..……………......25 .615 to 30 .105 MHz

FrequencyControl………………………………………………………………………………..…………..…….……PLL

Operating Temperature Range……………………………………..……..……………………………- 10° / + 50°C

DC I nput Voltage…………………………………………………....………………………..………....9 .0 V DC ±15%

Size………………………………………………………………….……..………..….…140( L) X 60( W) X 30( H) mm

Weight ………………………………………………………………………………..…………..……...……..……0.50 kg

2. RECEIVER

Receiving System……………………………….…………………………....Dual Conversion Super Heterodyne

I ntermediate Frequency…………………………………………...…….…1st I F: 10 .695 MHz, 2nd I F: 455 MHZ

Sensitivity……………………………………….…..............................….0 .5 µV for 20 db SI NAD in FM mode

Audio Distortion……………………………………………………….….……..…………….Less Than 8% @ 1 KHz

I mage Rejection……………………………………….…………………..………………………………………...60 dB

Adjacent Channel Rejection………………………………………….…………………………………………....60 dB

Signal/ Noise Ratio…………………………….…………………………….…………………………………..….45 dB

Current Drain at standby……………………….…………………………………………………………..……..60 mA

3. TRANSMITTER

Output Pow er…………………………………………………………………………………..……...….4W @ 9 .0 V DC

Modulation………………………………………………………………..………….…...………FM: 1 .6 KHz ±0 .2 KHz

Frequency response…………………………………………….…................................From 300 Hz to 3 .0 KHz

Output impedance………………………………………………………………………………RF 50 ohm Unbalance

Signal/ Noise Ratio…………………………………………………………………………………..………..40 dB MI N

Current Drain…………………………………………………………………………………………….….…….1300 mA

OPERATION INSTRUCTIONS

Having properly installed your batteries and hooked-up the antenna, you are now ready to operate your radio for optimum reception and voice transmission.

Turn the power “ON” with ON/OFF switch.

Set the desired channel.

Adjust the squelch control knob to reduce any undesirable background noise when no signal is being received. To do this, select a channel where no signal are present, or wait until signals cease on your channel. Then, rotate the squelch control knob clockwise to a point where the background noise disappears.

Note: When the squelch is set properly, the speaker will remain quiet until a signal is received. In order to receive weak signals, do not set the squelch too high.

Adjust the volume to the desired listening level.

To Transmit

Press and hold the push-to-talk button. Speak slowly and clearly in a normal voice two to three inches from the microphone. A buit-in modulation control circuit will automatically adjust the microphone input level. There is no need to speak loudly.

To Receive

Release the push-to-talk button.

THEORY OF OPERATIONS

TRANSMITTER

A. RF Amplification

The output of double AMP Q201 is fed through tuning T203 and T204 to the base of pre driver AMP Q202. The output is then supplied to RF driver AMP Q203. The output of Q203 is supplied with tuning circuit L204 and C214, C215, C216 and goes to the base of final RF AMP Q204. The output of Q204 is supplied to the antenna through L-C tuning circuit.

B. Circuit for Suppression of Spurious Radiation

The tuning circuit between the output of final AMP Q204 and antenna, 5-stage “PHI” network C221, C219, C220, L206, C223, C245, L207, C241, C228, C240, L208, C242, C230, C229, L209, C234, C233, C232, L210, C243, C235, C236 serves as a spurious radiation suppressor . This network also serves to match the impedance between TX power AMP Q204 and the antenna.

C. Circuit for Limiting Power

After finished all alignment, the constant voltage supply circuit limits the available power 4 W or slightly less. RV501 and corresponding three transistors Q509, Q502, Q501 control supply voltage of RF amplifier and other circuits.

Tune all the trimmer parts for maximum indication of RF power meter and adjust RV501 to make 4 w indication of RF power meter.

The tuning is adjusted so that the actual power is from 3.8 to 4.0 W. There are no other additional controls for adjusting the TX output power.

D. Modulation Control

a. FM

The mic input is fed to audio amplifier IC KIA324 which drives modulation varicap diode D302 in the VCO circuit. RV701 limits the incoming modulation audio levels to inhibit over modulation. While reading the modulation factor on the modulation analyzing equipment, adjust RV701 shall not exceed +/-1.6 KHz/Dev. After 20 dB up from

1.25KHz/1.2 KHz/Dev. Audio level b. AM

Modulation signal is fed to audio amplifier IC KIA324 and goes to TX voltage regulate circuit Q509, Q502, Q501 to make nominal signal level to achieve wanted modulation. To control incoming audio signal, R272 and corresponding ALC circuit limits the modulation shall not exceed +/-60% adjust RV702 +/-60% modulation under 1.0 KHz AF 60% mod plus 20 dB of audio signal.

E. Receiver

CB receiver is dual conversion supper-heterodyne type with the first IF 10.695 MHz and second IF 455 KHz. Receiver is separated two blocks, 1st IF section and 2nd IF section.

The PLL synthesizer supplies first local frequency 16.270 ~ 16.710 MHz.(for EU) and 16.90625 MHz ~ 17.29625 MHz (for UK) With the provided first local frequencies Q102,Q103 mixes the incoming RF signal to generate first IF signal. Mixed signals were filtered with the CF101 (10.695 MHz) crystal filter and other tuning circuits. Output signal of mixer is filtered with CF102 (455 KHz ceramic filter). The 455 KHz signal from the 2nd IF filter was amplified and limits internally. After amplification the signals fed the quadrature detector loop T104. Then we can see the recovered audio signals on Pin 12 for FM and Pin 13 for AM of IC1.

TROUBLE SHOOTING HINTS

ALIGNMENT PROCEDURE

ALIGNMENT PROCEDURE

Figure 3

Figure 4

RECEIVER SECTION

Test Equipment Required

•RF Signal generator (RFSG)

•SSVM

•Distortion meter

•DC power supply

ALIGNMENT PROCEDURE

Figure 5

Figure 6

Figure 7

PLL CIRCUIT BLOCK DIAGRAM

1. INTRODUCTION

The frequencies for transmitter and receiver first local frequencies are all derived from a single 10.240 MHz crystal by means of a phase locked loop. The first local oscillator frequencies are 16.270 MHz (CH 1) to 16.710 MHz (CH 40) for EU and 16.90625 MHz (CH 1) to 17.29625 MHz (CH 40) for UK. The second local frequency is fixed at 10.240 MHz to generate second IF 455 KHz. During transmit, The VCO of the PLL operates 13.4825 MHz (CH 1) to 13.7025 MHz (CH 40) for EU, 13.800625 MHz (CH 1) to 13.995625 MHz (CH 40) for UK the VCO frequency goes to the double circuit Q201, T203, T204 which doubles the frequency to generate 26.965 MHz (CH 1) to 27.405 MHz (CH 40) for EU and 27.60125 MHz (CH 1) to 27.99125 MHz (CH 40) for UK

The VCO operating frequency for the receiver is 16.270, 16.90625 MHz (CH 1) to 16.710, 17.29625 MHz (CH 40) as the first local oscillator, injected through the buffer AMP Q302 into the first fed balanced mixer Q102, Q103.

2. BASIC SYNTHESIZER SCHEME

The crystal frequency (10.240MHz) is divided by 1800 times to make 2.5 KHz which is fed to one side of the phase detector. The VCO output is divided by a programmable divider, and fed to other side of the phase detector Pin 11 of IC302. The feedback loop is closed by passing the phase detector output through an active low pass filter and using the output to control the VCO frequency through varicap diode D301.

Under locked conditions, both of phase detector input signal must be indential at 2.5 KHz. The VCO frequency is then given by:

FVCO / N = 0.0025 MHz or FVCO = 0.0025 x N MHz

Since “N” is an integer, the VCO frequency can be stepped up with 2.5 KHz increments. By suitable choice of “N” the desired output frequency can be obtained.

( SEE TABLE FOR OTHER CHANNELS)

The VCO frequency goes to the double circuit, which doubles the incoming signals.

Double output Frequency

Since all frequencies are obtained from the crystal controlled PLL oscillator, all outputs are coherent with the

crystal oscillator frequency and maintaining the same percentage accuracy.

INTERNAL BLOCK DIAGRAM

DIVIDE RATIO, VCO RX/TX FREQUENCIES FOR EACH CHANNEL OF “EU”

DIVIDE RATIO, VCO RX/TX FREQUENCIES FOR EACH CHANNEL OF “UK”

3.DESCRIPTIONS OF EACH BLOCK A. Introduction

The synthesizer is implemented with the following

Components:

-PLL IC (IC302)

-X-TAL (X302)

-VCO, VARICAP DOIDE (D301)

IC302 is a cmos LSI that includes most of PLL block and driver, the Q301, C305, C306, C304, C301 and T302, Varicap diode D301 are clapp oscillator circuit to operate as a VCO of the IC302. Q301 is a switching transistor to connect or disconnect the tuning capacitor in the VCO oscillator tank circuit for transmitter or receiver. Q304 works as a buffer AMP for RX local frequencies (16 MHz) and TX generating frequencies (13 MHz).

B. Reference frequency

The crystal, X302 (4.50 MHz) and other components of IC302 can make a reference frequency oscillator with internal amplifier.

C. VCO

Q301 and surrounding parts are consisting a clapp oscillator works as a VCO of IC302. the VCO can be oscillate over the required of 13.4825 MHz to 17.29625 MHz

D. Phase detector and VCO control

The detector is a digital phase comparator which compares the phase of the reference signal with programmable divider output square waves and develops a series of pulses whose DC level depends on the phase error of each signal.

E. Transmitter/Receiver buffer AMP

Output signal of Q301 is fed into buffer AMP Q302,

F. Transmitter doubler

The output signals of Q302 goes to an amplifier with tuning circuit Q201, T203, T204 which doubles incoming 13 MHz signals.

G. Switching of tuning capacitor in VCO

The VCO circuit must tune with a wide rang of frequencies 13.4825 ~ 13.7025 MHz (EU), 13.800625 ~ 13.995625 MHz (UK) for transmitter and 16.270~16.710 MHz (EU), 16.90625 ~ 17.29625 MHz (UK) for receiver. To comply above range of VCO, the tuning capacitance should switched for transmission or reception.

H. Receiver local oscillator outputs

First Mixer:

The secondary output signals is injected to the sources of 1st mixer Q102, Q103 in the 1st IF mixer section

Second Mixer:

The output of 10.24 MHz oscillator circuit with X101 is injected into the IF IC internally. Incoming IF signal and 10.24 MHz are mixed inside the IF IC to extract 2nd IF signal 455 KHz. FM,AM audio signals are recovered with the way of quadrature detector, AM signals are recovered with envelope detector.

4. FREQUENCY STABILITY

LET: Fo = Crystal oscillator frequency

Fr = Phase detector reference frequency

Fvco = VCO frequency

Ft = Transmit frequency

Then: Fr = Fo/1800

And under locked conditions: Fr = Fvco / N

WHERE, “N” is the programmable divider divide ratio.

THEN: Fvco = N X Fr

From which it can be seen, the percentage error in Ft is the same as the percentage error in Fo. The stability of the crystal oscillator is determined primarily by the crystal itself and having lesser deviation by the active and passive components of the oscillator. The choice of crystal and component is such that the required frequency stability is maintained over the required voltage

and temperature rang.

Printed Circuit Board