Alan HM135 User manual

HM135 Service Manual
Preliminary version Page 1 of 13
ALAN HM135
Mobile VHF Transceiver
Service Manual
Copyright 2004 by CTE International Italy; all rights reserved

HM135 Service Manual
Preliminary version Page 2 of 13
Contents
1TECHNICAL SPECIFICATIONS......................................................................................................................3
1.1 Test methods.................................................................................................................................................................3
1.2 Specifications table .......................................................................................................................................................3
2CIRCUIT DESCRIPTION .................................................................................................................................4
2.1 General information.......................................................................................................................................................4
2.2 Microprocessor/control ..................................................................................................................................................4
2.2.a PTT circuit ........................................................................................................................................................4
2.3 Front panel (head) circuitry ...........................................................................................................................................5
2.4 VCO / Synthesizer (PLL) ...............................................................................................................................................5
2.4.a Temperature-Compensated Crystal Oscillator (TCXO)....................................................................................5
2.4.b Voltage-Controlled Oscillators ..........................................................................................................................5
2.4.c Synthesizer.......................................................................................................................................................6
2.5 Transmitter ....................................................................................................................................................................6
2.5.a RF Power Amplifier...........................................................................................................................................6
2.5.b Antenna Switching............................................................................................................................................6
2.5.c Power control....................................................................................................................................................6
2.5.d Transmitter Audio Circuits ................................................................................................................................7
2.5.e Double-point modulation...................................................................................................................................7
2.6 Receiver ........................................................................................................................................................................7
2.6.a Receiver’s Front-End........................................................................................................................................7
2.6.b Local Oscillator (LO).........................................................................................................................................7
2.6.c Mixer.................................................................................................................................................................8
2.6.d FM Detector and Squelch.................................................................................................................................8
2.6.e Audio routing ....................................................................................................................................................8
2.6.f CTCSS/DCS signal routing ..............................................................................................................................8
2.6.g Selcall signal routing.........................................................................................................................................8
2.7 Signaling........................................................................................................................................................................8
2.7.a General.............................................................................................................................................................8
2.7.b CTCSS (Continuous Tone Coded Squelch System)/DCS (Digital Coded Squelch) ........................................9
2.7.c Selective call (Selcall) encoder.........................................................................................................................9
2.8 ON/OFF switch, rear connector and internal connectors ..............................................................................................9
2.8.a ON/OFF switch .................................................................................................................................................9
2.8.b Rear connector .................................................................................................................................................9
2.8.c Internal connectors (accessory board) .............................................................................................................9
3ADJUSTMENTS ............................................................................................................................................10
3.1 General........................................................................................................................................................................10
3.2 Initial Settings ..............................................................................................................................................................10
3.3 Applying power for the first time. .................................................................................................................................10
3.4 Loading the Firmware..................................................................................................................................................11
3.5 Programming the radio................................................................................................................................................11
3.6 Setting the Power Amplifier Bias .................................................................................................................................11
3.7 Setting the frequency and VCO’s tuning. ....................................................................................................................12
3.8 Setting the RF POWER...............................................................................................................................................12
3.9 Setting of modulation...................................................................................................................................................12
3.10 Setting of the Squelch Level........................................................................................................................................13

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1 TECHNICAL SPECIFICATIONS
1.1 Test methods
 ETS 300-086 / ETS 300-113 (optional “modem board”)
 IEC 529 IP54 and MIL STD 810 C/D/E
1.2 Specifications table
General
Characteristic Units Value/Measurements conditions
Frequency MHz from 136 to 174
Operating Band MHz 38
Number of Programmable Channels - up to 100
Channel Spacing KHz 12.5 / 20 / 25
Frequency Steps KHz 5 / 6.25
Rated Power Supply Vcc 13.8
Stand-by 0.4 (or less)
RX 0.6 @ the maximum AF power
Current drain A
TX 5 (@ 25 W) / 3.5 (@ 10 W) / 2.4 (@ 4 W)
Antenna Impedance Ohm 50
Speaker Impedance Ohm 8
Frequency Stability ppm ±5
Operating Temperature Range °C from –25 to +55
Relative Humidity % 90 (non condensing)
Transmitter
Output Power (±1 dB) W 10 / 25 (depending on the version)
from 9 KHz to 1 GHz < -36 dBmSpurious Emissions µW
from 1 to 4 GHz < -30 dBm
Modulation System - FM (F3E) / PM (G3E)
Maximum Deviation KHz ±2.5 (@ 12.5 KHz) / ±5 (@ 25 KHz)
Adjacent Channel Power Attenuation dB < -60 (@ 12.5 KHz) / -70 (@ 20-25 KHz)
Receiver
Configuration Double Conversion Superetherodyne
Sensitivity (at 12 dB SINAD) µV < 0.3
Squelch Sensitivity (SINAD) µV 0.25 with 3 dB hysteresis
Selectivity (Adjacent Channel) dB At least -60 (@ 12,5 KHz) / -70 (@ 25 KHz)
Spurious Response Rejection dB > 70
Intermodulation dB > 65
Audio Output (1 KHz at 5% T.H.D.) W 4 (built-in internal speaker) / 10 (external audio output)
Mechanical Specifications
Type of construction - Metallic cabinet with detachable front panel
Size mm 180x57x28 with front panel / 174x48x150 main unit only
Weight Kg 1.4
Microphone connector - RJ
Rear I/O connector - 25-pins DB type
Shock resistance - Meets MIL STD 810 specifications
Moisture & Dust Resistance - According to the IEC529 and IP54 regulations

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2 CIRCUIT DESCRIPTION
2.1 General information
The HM135 is basically divided into 2 printed circuit boards: Main board and Head. Circuitry and signals can be
divided in the following sections:
 Microprocessor/control
 Front panel (head) circuitry
 VCO / Synthesizer (PLL)
 Transmitter
 Receiver
 Errore. L'origine riferimento non è stata trovata.
 ON/OFF switch, rear connector and internal connectors
Refer to the Block Diagram and the Schematics.
2.2 Microprocessor/control
The microprocessor DD5 is constantly operating when the radio is turned ON. It is continuously monitoring the
keyboard, the PTT line and other internal inputs such as the squelch detect, etc. When a change occurs, the
microprocessor makes the appropriate response according to its program in order to control the all radio
functions. On channel change, the Radio emits a beep and the synthesizer is loaded with the correct frequency
information. The microprocessor runs off a 8 MHz oscillator which is composed of X3, C353, C354 and R319.
When the radio is first turned on, the microprocessor reads the radio status from the EEPROM DD3 which
contains all the radio’s parameters.
The microprocessor determinates the receive frequency codes, then loads the synthesizer via its pins 42 (line
PLL_LE), 43 (line PLL_DATA) and 46 (line PPL_CLK).
Pin 40 outputs a PWM signal which is converted by DA18:B into a CC voltage at its output (line RF_PWR_CTRL)
which controls the RF output power.
Pins 37 and pin 39 outputs a PWM signal which are used, respectively, to generate the Selcall signal (line
MCU_SELCALL_PWM) and CTCSS/DCS signal (line MCU_CTCSS_DCS_PWM) as further explained. The
digital signals coming from the ADC converters which drive the microprocessor in order to decode the Selcall and
CXTCSS/DCS signals are applied, respectively, to pin 59 (line ADC_HI_SPEED_DATA_RX) and pin 60
(ADC_lo_SPEED_DATA_RX).
The firmware program interface is made by means of the connector XP3
The microprocessor is fitted with an internal program flash memory as well, therefore functions can be
customized, if necessary, upon specific request from the customer.
2.2.a PTT circuit
The PTT switching is totally controlled by the two microprocessors (DD5 in the main board and DD800 in the front
board in the front panel): when the PTT is pressed, the line AUX_PTT goes low, so the transistor VT806 changes
the status of the pin 20 of microprocessor DD800 which is “informed” that the radio is in TX mode (i.e. PTT is
pressed), so it changes its output at pin 22 putting the low level at pin 8of the connector XT802 which is
connected to the main PCB with the connector XT2. This means that pin 8of XT2 (line
HANDSET_PTT_TO_MPU) goes low. This line is connected to the VT56 which changes the status of pin 26 of
the microprocessor DD5 from hi to low. Now the microprocessor DD5 is also “informed” that the radio is in TX
mode, so it can control the +8V voltage which is alternatively fed to the TX or RX stages according to the radio’s
status. Pins 29 (line TX_FROM_MCU) and 30 (line RX_FROM_MCU) control the +8V power switches which
alternatively outputs this voltage to the RX section (line +8V_RX) with VT42 or to the TX one (line +8V_TX) with
VT41.
The transistor VT805 is controlled by the pin 19 of the microprocessor DD800 and it is used to eventually disable
all the over stated PTT chain according to the radio’s status (e.g. busy lock out, timeout timer etc).

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2.3 Front panel (head) circuitry
The microprocessor DD800 runs off a 8 MHz oscillator which is composed of X800, and R829. DD800 is basically
used to control the LCD unit XT80, to decode the commands coming from the front keypad S801 to S808) as well
as to switch the front LEDs DA800. It is also used to light up the LCD backlight (VD800 to VD805) as well as for
the PTT circuit as over stated.
The negative voltage necessary for the LCD is created by a charge pump which consists of VT815, VT813,
VT812, VD809 and VD808. The output (line –8V) is fed to the regulator DA804:A which outputs the line VD in
order to supply the LCD unit.
The hang-up functions work this way: the line AUX_HOOK is connected to the microphone’s hook and it’s
normally grounded (microphone hooked). When the mike is removed from its hook, the line AUX_HOOK changes
its state driving the transistor VT809. This changes the status of the pin 21 of the microprocessor DD800 which
opens the monitor through a command sent to the main microprocessor DD5 through a serial command.
2.4 VCO / Synthesizer (PLL)
This section basically consists of the Temperature-Compensated Crystal Oscillator (TCXO), Voltage Controlled
Oscillators (VCOs), Synthesizer and the Loop Filter.
2.4.a Temperature-Compensated Crystal Oscillator (TCXO)
The reference oscillator is composed by the temperature compensated crystal X2 and related circuitry (DA1:A.
VD19, VD20, VT21 and VT20), RP2 is used to adjust the oscillator on frequency (12.8 MHz) at room temperature.
The reference oscillator is held within the specifications ±5 ppm from -25 to +55℃.
2.4.b Voltage-Controlled Oscillators
The receive VCO consists of VT11, CV1, VD6 and VD9. This VCO oscillates at 45.1 MHz above the programmed
receive frequency (i.e. from 181.1 to 219.1 MHz for the 135-174 MHz range). The VCO’s oscillating frequency is
tuned by the varactors VD6 and VD9.
The transmitter VCO consists of VT17, CV2, VD11-VD12 and VD13-VD14 and oscillates directly to the TX carrier
frequency range (i.e. from 135 to 174 MHz range). The TX VCO is directly frequency-modulated by means of the
varactor VD15 which is driven by the modulating signal (line A) regulated by the trimmer RP4. This is part of the
double-point modulation and works mainly in high AF modulating frequencies), the other part of the double point-
modulation is explained in the par. “Transmitter Audio Circuits”.
The tuning voltage for the VCOs is supplied from the output of the Loop Filter made with R73, R74, R78, C99,
C100 and C101.
Only one of the VCOs runs at a time. In RX the line RXC (which is obtained from the +8V_RX line coming from
the voltage switch VT41) is high enabling the RX VCO via the transistor VT16. During this time the line TXC
(which is obtained from the +8VTX line coming from the voltage switch VT42) is low, so the TX VCO is disabled.
When the PTT is pressed, the RXC line becomes low switching the RX VCO off. At the same time the line TXC
goes high activating the TX VCO via the transistor VT18.
The output of the VCOs are AC coupled (C91 and C109) and sent to the synthesizer buffer VT19, then sent to
DA5 for an additional buffering. The output of DA5 is connected to the low-pass filter (L27, L28, L29 and related
capacitors), then directly sent to the TX stages (line HET_TX which is sent to the pre-driver amplifier VT24) or RX
stages (line HET_RX which is sent to the RX mixer A1) due to the RF switching action provided by VD16 and
VD17 which are controlled by the lines +8VRX and 8V_TX_F respectively (this last line is obtained from the line
+8VTX passed through the filter created with L52, L53 and related capacitors). The output from the VCO
necessary to feedback the PLL IC DA3 (i.e. line PLL_RF send to pin 8) is directly output from VT19 and fed
through R106, C362 and C134. , whilst the other part of the signal is fed to DA5, then passed through the low-
pass filter (L27, L28, L29, C130, C132, C133 and C131). Diodes VD16 and VD17 act as signal switches in order
to feed the signal to RX or TX stages at the appropriate time according to the switching voltages which are,
respectively, the lines +8VRX and 8V_TX_F.
The PLL IC DA3 receives the reference signal from the TCXO (pin 1) and the feedback from the VCO (pin 8). The
synthesizer is tuned in 5.00 KHz or 6.25 KHz steps. The output from the PLL IC (pin 15 and 16) is used to drive
the PLL charge pump which consists of VT12, VT13, VT14 and VT15, then the charge pumps sent the output to
the PLL filter in order to close the loop.

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2.4.c Synthesizer
The PLL IC frequency synthesizer is a large scale monolithic synthesizer integrated circuit DA3.
The synthesizer IC contains a dual modular prescaler, programmable divide-by-N counter, prescaler control
(swallow) counter, reference divider, phase detector and unlock detector.
RF output from the active VCO is AC coupled to the synthesizer DA3 prescaler input at Pin 8. The divide-by-N
counter chain in DA3, consisting of the dual-modulus prescaler, swallow counter and programmable counter,
divides the VCO signal down to a frequency very close to 5.00 KHz or 6.25 KHz which is applied to the phase
detector. The phase comparator compares the edges of this of this signal with that of the 5.00 KHz or 6.25 KHz
reference signal from the reference divider and drives the external charge pump (VT12, VT13, VT14 and VT15).
The synthesizer unlock detector circuit prevents the operation of the transmitter when the phase lock loop (PLL) is
unlocked. The following discussion assumes the unit has been placed in the transmit mode. DA3 lock detector Pin
7 goes high when the PLL is properly locked. This high level is applied to pin 21 of the microprocessor DD5. A
software timing routing brings the pin 28 of the microprocessor DD5 low making the line PA (connected via R323
and C361) low as well. With the PA line low, VT28 is cut off and VT27 biases the RF driver (VT23) and RF power
amplifier (VT22) which enables transmission.
When the PLL become unlocked, the lock detector at DA3 pin 7will begin pulsing low. A RC circuit (R311 and
C347) converts pulsing low to a low level for the microprocessor (pin 21). The microprocessor then changes the
PA line to a high switching the transistor VT28 on. This cuts off the transistor VT27 which is not able to supply the
bias to the RF driver and RF power amplifier disabling the transmission. Therefore, the transmitter remains
disabled while the phase locked loop remains unlocked.
2.5 Transmitter
2.5.a RF Power Amplifier
The TX RF amplifier is made with 3 stages: VT24 is the pre-driver, VT23 is the driver and VT22 is the Power
Amplifier (PA). Output from the last PLL buffer DA5 (line HET_TX) feeds the pre-driver amplifier VT24. The output
signal from VT24 feeds the driver amplifier VT23, whose output from the driver stage feeds the final RF power
amplifier VT22 to produce the rated output power of 25 watts. The output of the power amplifier is applied to the
RX/TX switch made with VD21, VD22 and related circuitry, then to the low-pass filter (consisting of L46 to L49
and connected capacitors) and then to the SWR coupling line TA1 which is directly connected to the antenna
connector.
The 8V_TX_F line supplies the total bias current to the bias regulators. Pre-driver is biased by VT25 and both the
driver and power amplifier are biased by the same transistor VT27. Obviously, the output of VT27 biases these
two stages via 2 different trimmers, which are RP5 for the driver (about 200 mA) and RP6 for the power amplifier
(about 300mA).
2.5.b Antenna Switching
Switching of the antenna between the transmitter and the receiver is accomplished by the antenna
transmit/receive switch consisting of diodes VD21 and VD22 in conjunction with C189, C190 and L44. In reception
mode both the diodes are unbiased, so the RX signal coming from the ANTENNA line passes through the
coupling line TA1, the low pass filter (L49, L48, L46, C193, C194 etc.), going to the receiver’s front-end input (line
RF_RX) via L144. In the transmit mode, switched +8VTX is applied to the base of VT26 through R142 and R143
hard forward biasing the two diodes on. VD21 thus permits the RF power from output of the power amplifier to
flow to the input of the low-pass filter. At the same time, VD22 avoids that the residual RF coming from the
transmitter is accidentally sent to the receiver by removing it with the 3 capacitors C183, C184 and C185.
2.5.c Power control
Output power is picked up from the output coupling line TA1 and sent to the diodes VD24 and VD26. The first one
detects the forward power and the second one the reflected power which drops, respectively, across R145 and
R156. These two signals (respectively the lines FWD_PWR and REFL_PWR) are fed separately to an operational
amplifier (DA6:A and DA6:B) and combined into a third one (DA6:C) which regulated the output power according
to the input signal. The calibration of the output power is provided by the trimmer RP7 which controls DA6:C. Its
output is connected to the transistor VT27 which provides the bias for the driver and power amplifier closing the
power control loop. In case of excessive S.W.R., the output power is automatically reduced in order to protect the
final stage.

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2.5.d Transmitter Audio Circuits
The speech audio coming from the MIC connector (line AUX_MIC) is applied to the FET VT804 which acts as
sensitivity switch (function high/low MIC sensitivity) in 2 levels and is directly controlled by the microprocessor (pin
27) via the transistor VT807. The signal is then fed to the amplifier made by DA801:A (DA801:B is used to supply
the reference voltage at its positive input) providing a stronger speech signal (line MIC_INPUT) which is fed to the
6dB per octave pre-emphasis circuit provided by the capacitor C277 and the resistor R213 and applied to pin 6of
DA11:B.
 NOTE: Between the C277 and the MIC_INPUT line, the transistor VT48 acts as a mute switch which disable the speech
audio when a Selcall is sent.
Selcall audio PWM signaling coming from the pin 37 of the microprocessor (line MCU_SELCALL_PWM) is fed to
the 3 KHz low pass filter which consists of DA9:B and related circuitry. Its output is then fed to the input of the
DA11:B, so routed the same way of the speech audio.
The speech/Selcall signal is applied to the input of DA11:B which limits the peak-to-peak output, then is fed to the
pin 3of IC DA10 which is a double digital audio regulator. After the level regulation, the speech/Selcall is output at
pin 11 and sent to the first input (pin 9) of DA9:C in order to be summed with the CTCSS/DCS signal.
 NOTE: The level regulation of DA10 comes in form of digital data from the pins 6, 7and 8(lines POT_DATA, POT_CLK
and DAC_CS respectively) which are directly controlled by the microprocessor DD5 (pins 43, 46 and 36 respectively) via
related logical inverters.
CTCSS/DCS sub-audio tone PWM signaling coming from the pin 39 of the microprocessor (line
MCU_CTCSS_DCS_PWM) is fed to the CTCSS/DCS 300 Hz low pass filter which consists of DA9:A and related
circuitry, then fed in the pin 2 of the IC DA10 which regulates the level and outputs the regulated CTCSS/DCS at
its pin 12. This signal is then applied to the second input of DA9:C in order to be summed with the speech/Selcall
signal.
DA9:C sums the two signals (speech/Selcall coming from pin 11 of DA10 and CTCSS/DCS coming from pin 12)
feeding its combined output to DA9:D which is a 3 KHz low pass filter. The output of DA9:D is then applied to pins
4and 5of the DA10.
2.5.e Double-point modulation
The outputs (lines REF_MOD and VCO_MOD) coming, respectively, from pins 10 and 9of DA10 are fed to the
PLL area. The line REF_MOD is directly applied to the trimmer RP3 which provides the Ref. Modulation control
(low audio frequencies) directly applied to the TCXO. The line VCO_MOD is applied via the resistors R116 to the
trimmer RP4 which provides the VCO modulation control (high audio frequencies) directly sent to the TX VCO.
2.6 Receiver
2.6.a Receiver’s Front-End
The RX signal coming from the antenna connector is fed in sequence through the coupling line TA1, the low pass
filter (consisting of L46 to L49 and connected capacitors) and the antenna switching (VD21 and VD22). The
output of the antenna switching (line RF_RX) is sent to input of the receiver and coupled to the input band-pass
filter. The transistor VT2 is the front-end amplifier and its output is applied to the second band-pass filter (L2, L3,
L4, L5 and related capacitors). The output from the band-pass filter is applied to the pin 4of the RF mixer A1.
The diode VD1 is used for the function local/distance. Normally the line LOCAL_DIST issued by the pin 25 of the
microprocessor (properly adapted by R317 and C352) goes to high so VT1 is switched on forward biasing the
diode VD1. This provides a bypass of the resistor R5 for the RF, so the RF signal fed to the mixer is higher
(distance mode). On the other side, if the line LOCAL_DIST drops to low, the diode VD1 is not forward biased and
the RF is attenuated of 10dB approx. due to the R5 (local mode).
2.6.b Local Oscillator (LO)
As already explained in the PLL section, the output coming from the RX VCO (working at 45,1 MHz above the RX
frequency) is sent to the synthesizer buffer VT19, then sent to DA5 for an additional buffering. The output of DA5
is connected to the low-pass filter (L27, L28, L29 and related capacitors), then sent to the RX stages (line
HET_RX) which is sent to the RX mixer A1 via an attenuator which consists of R13, R14 and R15.

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2.6.c Mixer
The mixer LO frequency is 45.1 MHz above the desired receiver frequency. When the receiver frequency is
present, the mixer output will be a 45.1 MHz signal. The mixer output is peaked for 45.1 MHz by means of the
diplexer filter (L12, L15, C56, C46, C47, R31, R35 and R36) and the RF amplifier VT7, then signal is filtered by
crystal filters XF1A and XF1B and amplified by VT5 and VT4 before being applied to the input (pin 16) of the IF IC
DA2.
Inside DA2, the 45.1 MHz IF signal is sent to the input of the second mixer with a LO frequency of 44.645 MHz
(the frequency of the crystal X1 is 44.545 MHz, but it is 100 KHz shifted by means of the connected components
C68, C69 and C70, L17, R54 and R51). The output of the second mixer is sent from pin 3of DA2 to the 455 KHz
ceramic filters CF2 (for 12,5 KHz bandwidth) or CF1 (for 25 KHz bandwidth) which filter the second mixer’s output,
then fed to the second IF signal input of DA2 (pin 5). The mixer’s output is then fed to the internal limiting amplifier
and then on to the FM decoder.
 Note: the switching of the two filters CF2 or CF1 is accomplished by means of the line 12.5_25 coming from the pin 24 of
the microprocessor DD5 which drives, in sequence, the transistor VT10 and the switches DD1 and DD2.
2.6.d FM Detector and Squelch
The FM detector output (pin 9of DA2) is used for squelch, decoding tones and audio output. The setting of the
squelch adjustment RP1 sets the input to the squelch amplifier.
The squelch amplifier is internal to DA2 and its output is fed to an internal rectifier and squelch detector.
The output on DA2 (pin 14) signals the microprocessor DD5 with a low level to unmute the radio. The audio is
unmuted by using the line RX_MUTE sent from the pin 50 of the microprocessor DD5 to the mute switch VT54
controlled by the transistor VT55.
2.6.e Audio routing
The detector’s audio output (line DETECTOR_AUDIO) is fed to DA13:A and DA13:B (3 KHz low-pass filter
deeply described in the next paragraph), then routed to the 300 Hz audio high-pass filter which consists of
DA12:A and DA12:B. The output of the audio high-pass filter feeds the AF de-emphasis (DA15:A) and AF pre-
amplifier (DA15:B), then the volume control provided by the IC DA16. The audio is then routed to Pin 1and 9of
the audio amplifier DA14.
VT61 is used to enable/disable the internal speaker and is controlled by VT52 by means of the signal
INT_SPEAKER_OFF sent by the pin 48 of the microprocessor DD5.
If the radio is in alert mode, the microprocessor DD5 generates an alert signal at its pin 38, this signal (line
ALERT) is injected in the low-pass filter (DA15:C) and routed at the input of the AF pre-amplifier DA15:B by
means of the resistor R269.
2.6.f CTCSS/DCS signal routing
Similarly to the audio routing the detector’s audio output (line DETECTOR_AUDIO) is fed to DA13:A and DA13:B
which make the tone (CTCSS and DCS) 3 KHz low-pass filter, however the output of the low-pass filter (line
TO_CTCSS_DATA_FILTER) is directly routed to the second stage tone filter which consists of DA17:A, DA17:B
and DA17:C. The output of this filter (line ADC_LO_SPEED_DATA_RX is then sent to the microprocessor DD5
(pin 60) in order to be decoded.
2.6.g Selcall signal routing
The Selcall signal follows the same routing of the audio one, but it’s picked up at the output (pin 1) of DA15:A (line
TO_CCIR_DATA_FILTER), then fed to DA17:D and sent (line ADC_HI_SPEED_DATA_RX) to the
microprocessor (pin 59) in order to be decoded.
2.7 Signaling
2.7.a General
The microprocessor is fitted with a ADC/DAC converter built-in, so it provides generating and decoding the tones
for selective calls, CTCSS and DCS. It can do that without using any other external I.C.s, but only by means of
some external circuitry. The deviation of the selective call can be adjusted by the trimmer IRV1.

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The microprocessor manages the analogue switches for the scrambler as well, which is base-band-inversion type.
2.7.b CTCSS (Continuous Tone Coded Squelch System)/DCS (Digital Coded Squelch)
CTCSS signals and DCS signals are synthesized by the microprocessor DD5 (pin 39 - line
MCU_CTCSS_DCS_PWM) and appear as PWM, then smoothed by the CTCSS/DCS 300 Hz low pass filter which
consists of DA9:A and related circuitry to produce an acceptable sine wave output. The output of the filter is fed in
the pin 2 of the IC DA10 which adjusts the level and outputs the regulated CTCSS/DCS at its pin 12. This signal is
then applied to the second input of DA9:C in order to be summed with the speech/Selcall signal.
The CTCSS/CTS decoding is provided by the microprocessor DD5 (pin 60) which gets the proper signal from the
detector as explained in par. “CTCSS/DCS signal routing”.
2.7.c Selective call (Selcall) encoder
Similarly to CTCSS/DCS, Selcall signals are also generated and decoded by the microprocessor DD5. Selcall
encoding audio PWM signaling coming from the pin 37 of the microprocessor (line MCU_SELCALL_PWM) is fed
to the 3 KHz low pass filter which consists of DA9:B and related circuitry. Its output is then fed to the input of the
DA11:B, so routed the same way of the speech audio.
The speech/Selcall signal is applied to the input of DA11:B which limits the peak-to-peak output, then is fed to the
pin 3of IC DA10 which is a double digital audio regulator. After the level regulation, the speech/Selcall is output at
pin 11 and sent to the first input (pin 9) of DA9:C in order to be summed with the CTCSS/DCS signal.
The Selcall decoding is provided by the microprocessor DD5 (pin 59) which gets the proper signal from the
detector as explained in par. “Selcall signal routing”.
2.8 ON/OFF switch, rear connector and internal connectors
2.8.a ON/OFF switch
The line ON/OFF_SWITCH is normally pulled up by the resistor R182. When the front ON/OFF switch is switched
on, this line becomes low, so the zener VD32 can bias the transistor VT35 which activates the main electronic
power ON/OFF switch VT33 which feeds the main voltage to the regulators DA7 (+8V) and DA8 (+5V). The diode
VD37 acts as a typical protection against polarity inversion.
2.8.b Rear connector
The rear connector XT3 accomplishes a variety of connections and functions allowing to connect the radio to
many kinds of devices. For example:
 Pins 3and 16 (lines EXT_SPEAKER- and EXT_SPEAKER+) can be connected to an appropriate external speaker
 The line AUX_OUT_FROM_MPU coming from the pin 16 of the main microprocessor DD5 drives the transistor VT33 which
can switch ON/OFF by software a 5,6 V voltage at pin 1(line AUX_OUT) of XT3 is an auxiliary output programmable by
firmware.
 The pin 13 of XT3 duplicates the hang up function normally provided by the microphone hang up: grounding or not the line
HUNG_UP reflect a status change in the line HANG_UP_TO_MPU via the zener VD27 and the transistor VT29
 Pin 9duplicates the PTT connection normally provided by the microphone connector in the front panel. Its line
EXTERNAL_PTT drives the zener VD30 and the transistor VT32 which reflect a status change in the line PTT_TO_MPU
2.8.c Internal connectors (accessory board)
The internal connectors XP1 and XP2 are used to internally fit a variety of option boards, such as scrambler
modules, audio processing modules etc. For this reason there are many contacts in parallel with XT3, e.g. XP1
has AUX_OUT at pin 13 and EXTERNAL_PTT at pin 1. Moreover, the two connectors have other specific lines in
order to handle a large number of internal signals, e.g. flat unsquelched RX audio at pin 14 pf XP1 and
microphone input/output at pins 1and 2of XP2.

HM135 Service Manual
Preliminary version Page 10 of 13
3 ADJUSTMENTS
3.1 General
Adjustment trimmer potentiometer/capacitors in the HM135 main unit:
Ref. Designator Used for…
RP1 Squelch Level Adj.
RP2 Frequency Adj.
RP3 Deviation Balance ( Reference Oscillator Modulation Level)
RP4 Maximum Deviation Adj.
RP5 Transmitter Driver Bias Adj.
RP6 Transmitter Power Amplifier Bias Adj.
RP7 Transmitter Maximum Power Adj.
CV1 Receiver VCO Adj.
CV2 Transmitter VCO Adj.
3.2 Initial Settings
 DO NOT CONNECT THE RADIO TO THE POWER SUPPLY BEFORE AND DURING INITIAL SETTINGS
OF CONTROLS.
1) Connect an ohmmeter between the wiper of RP3 and Ground. Turn RP3 in CCW direction until readings of the ohmmeter
are within 100 to 500 Ohm
2) Connect an ohmmeter between the wiper of RP5 and Ground. Turn RP5 in CCW direction until readings of the ohmmeter
are within 100 to 300 Ohm
3) Connect an ohmmeter between the wiper of RP6 and Ground. Turn RP6 in CCW direction until readings of the ohmmeter
are within 100 to 300 Ohm
4) Connect an ohmmeter between the wiper of RP7 and Ground. Turn RP7 in CCW direction until readings of the ohmmeter
are within 200 to 500 Ohm
3.3 Applying power for the first time.
 RF Power amplifier and AF Power Amplifier of the radio are connected to the power supply before the
internal ON/OFF Switch, i.e. supply voltage is present even if the ON/OFF Switch is in OFF position. It
is strongly recommended to disconnect the radio from the plus of the power supply if full switching
OFF is needed.
 Keep the minus of the Power Supply Unit connected to the GROUND.
 Use pre-programmed and checked Front Panel.
Control Function Initial Settings
RP1 Squelch Level Adj. Center
RP2 Frequency Adj. Center
RP3 Deviation Balance Minimum (CCW), see note1.
RP4 Maximum Deviation Adj. Center
RP5 Transmitter Driver Bias Adj. Minimum, see note 2
RP6 Transmitter Power Amplifier Bias Adj. Minimum, see note 3
RP7 Transmitter Maximum Power Adj. Minimum, see note 4
CV1 Receiver VCO Adj. As is
CV2 Transmitter VCO Adj. As is

HM135 Service Manual
Preliminary version Page 11 of 13
 Radio contains a number of ESD, most sensitive components, without build-in protection are LDMOS
RF Power transistors.
1) Check connection between the Front Panel and the Main Unit.
2) Set ON/OFF Volume Potentiometer of the Front Panel Fully CCW (Switched Off)
3) Connect the radio’s Antenna connector to a Communication Tester, preset in Transmitter Measurement mode.
4) Set a Regulated Power Supply unit, capable to deliver at least 7A of DC Current, to 13.2V and current limit to 1A.
5) Connect the radio to the Power Supply Unit. Check the current. It must be below 30mA.
6) Switch ON the radio. Check the current, it must be below 0.5A.
7) Check Radio’s Internal Power Supply as follows:
 Between pin 1of DA7 (KIA7808API) (the pin, nearest to the Audio Amplifier IC) and ground – plus 13.2V
 Between pin 3of DA7 and ground – between 7.6 and 8.4V
 Between the positive electrode of C247 and ground - between plus 4.75 and 5.25V
 Between the positive electrode of C358 (near pin 1of uP DD5) and ground plus 3.3, plus/minus 0.15V.
8) Switch off the radio.
3.4 Loading the Firmware
1) Connect a Firmware Programmer to the XP3, JTAG Connector.
2) Power On the radio
3) Load the firmware
4) Power Off the radio
5) Disconnect the Programmer.
6) Switch ON the Radio. Usually it will respond with BAD CRC Message on LCD. It is OK. Switch OFF the Radio.
3.5 Programming the radio
1) Connect the programming cable to radio’s Microphone Connector.
2) Press the F1 key, keep it pressed and switch ON the radio. Radio will respond with Programming... on the LCD and
Orange light of front panel diode. Release F1 Key.
3) Program the radio using Factorytest1.hpv settings file. It includes 6 channels:
 CH1 - 135.100 MHz, 25 KHz Channel spacing, No CTCSS , No DCS, No Sellcall
 CH2 - 155.100 MHz, another settings as per CH1
 CH3 - 173.900 MHz, another settings are as per CH1
 CH4 - 135.100 MHz, 12.5 KHz Channel spacing, No CTCSS , No DCS, No Sellcall
 CH5 - 155.100 MHz, another settings as per CH 4
 CH6 - 173.900 MHz, another settings are as per CH 4
 CH7 - 155.1 MHz, 25 KHz spacing, CTCSS 67Hz on RX ant TX.
 CH8 - 155.1 MHz, 25 KHz spacing, CTCSS 254.1 Hz.
 CH9 - 155.1 MHz 25 KHz spacing , SELLCALL CCIR 12345 both RX ant TX
4) Switch OFF the radio and disconnect the programming cable.
5) Connect the microphone to the radio.
3.6 Setting the Power Amplifier Bias
1) Connect TP1, VCO voltage test point, to the ground.
2) Connect a 200 to 330 pF Disc Capacitor between the common point of VD16, VD17 and R98 and the ground.
3) Power ON the Radio. Push the PTT of the Microphone.
4) Note the current , it must be approx 400 to 500mA.
5) Turn slowly the RP5, TX Driver Bias in CW direction until the current from power supply is increased with approx. 300 mA.
Note the current.
6) Turn slowly RP6, TXPA Bias in CW direction until the current is increased with approx. 300mA. Keep the current absolute
value below 1.1 A.

HM135 Service Manual
Preliminary version Page 12 of 13
7) Release the PTT.
8) Power Off the radio. Disconnect the short from TP1. Keep the capacitor (step 2 above) connected.
3.7 Setting the frequency and VCO’s tuning.
1) Switch the radio ON
2) Go to CH3 (173.9 MHz)
3) Connect an oscilloscope between TP1 , located in the center of VCO shield, and ground. Turn CV1, RX VCO ADJ, slowly
until the voltage at TP1 is between 6.5 and 7.1VDC, without notable ripple.
4) Press the PTT. Turn CV2 TX VCO ADJ slowly until the voltage at TP1 is between 6.5 and 7.1 VDC, without notable ripple.
Release the PTT
5) Switch to CH1 (135.1 MHz). The voltage at TP1 must drop to 1.8 to 3V. Press the PTT. The voltage must be within 2 and
3.1V.
6) Repeat all above, if necessary.
7) Remove the 300pF capacitor (step 2 of the paragraph “Setting the Power Amplifier Bias” above).
8) Switch to CH2 (155 MHz).
9) Go to transmit (PTT) and turn slowly RP7, maximum TX Power until the output power is reached approx 5 to 8W.
10) Rotate RP2, FREQUENCY ADJUST until the frequency is within 155.000 MHz plus/minus 200Hz. Release the PTT.
11) Change the channel to CH1, check the frequency, it must be 135.000 MHz plus/minus 200Hz.
12) Go to CH3, 173.900 MHz, check the frequency, it must be 173.900 MHz plus/minus 280Hz. Realign the RP2 to tune the
frequency as near as possible to 173.9 MHz.
3.8 Setting the RF POWER.
1) Switch to CH2, 155.1 MHz. Set the power to High (20W).
2) Press the PTT. Turn RP7, Maximum Power ADJ, until the power is set to 20 plus/minus 1W.
3) Check the power on CH1 and CH3 . It must be between 18.5 and 20W.
4) Change the power on CH1 to CH3 to LOW. Check the power, it must be between 9 and 10 W.
3.9 Setting of modulation
1) VERY IMPORTANT! Switch off all the modulator filters in the deviation meter (communication tester) before this
measurement. Radio’s modulation input used for this setting is (i.e. without pre-emphasis).
2) Disconnect the microphone from the radio. Set the radio to CH2 155.1 MHz
3) Connect an AF Generator between the pin 7of rear DB25 connector (TX AF IN) and Ground (pin 14).
4) Short pin 9(External PTT) of rear DB25 Connector to the ground. It is equivalent to pressing the microphone PTT.
5) Set the AF Generator to 2000 plus/minus 50Hz and output level of 1V.
6) Adjust the RP4, maximum deviation control until the deviation is set to 4.6 kHz ((peak to peak)/2)
7) Decrease the output of the AF generator until the deviation is set to 2000 plus minus 50Hz.
8) Keeping the level of the AF generator the same (it must be approx 100mV) decrease the generator frequency to 100Hz.
9) Turn RP3, deviation balance until the deviation is set to 2000 Hz. Observe the demodulated signal, it must be clean , without
notable higher (reference) frequency ripple. Presence of ripple means that balance is not set properly. Near the balance the
ripple disappear.
10) Check the deviation at 300 Hz, 500 Hz, 1 KHz, 2 KHz, 2.7 KHz. It must be within 1.8 and 2.3 KHz. Repeat steps 5 to 9, to
adjust the deviation as near as possible to 2kHz if necessary.
11) Increase the level of the AF Generator to 1V. Check the deviation at 1kHz, it must be approx. 4.6 kHz.
12) Remove the short at pin 9. Disconnect the AF Generator.
13) Switch to CH7. Short pin 9(Ext. PTT) to the ground. Check the deviation. It most be 500 plus/minus 120 Hz.
14) Go to RX, change the channel to CH8. Check the deviation, it must be between 400 and 650Hz.
15) Change the channel to CH9. Press CALL1. Note the maximum measured deviation. It must be between 2.55 and 2.9 KHz.

HM135 Service Manual
Preliminary version Page 13 of 13
3.10 Setting of the Squelch Level.
1) Switch the radio to CH2, 155.100 MHz.
2) Turn RP1, SQUELCH LEVEL ADJ, until radio opens without signal applied to the antenna input.
3) Connect a SINAD meter to pin 5of rear DB25 connector. Switch off the CCITT filter the SINAD meter. Connect a RF
generator, tuned to 155.100 MHz to the radio’s antenna connector
4) Set the RF generator modulation frequency to 1kHz and the deviation to 3 KHz. Set the RF output of the generator to –87
dBm (10 uV).
5) Decrease the level of RF generator until SINAD meter reads approx 8 to 9 dB. Note the RF generator settings.
6) Decrease the RF generator level with 6 dB. Turn slowly RP1, until the squelch close.
7) Increase the level of RF generator slowly until Squelch opens. Note the RF level. It must be approx the same, as set in step
5 above. If not, set the level to the same, noted in step 5 and repeat the settings of RP1 again.

ALAN HM135
TEST POINTS AND PCB LAYOUTS

pdfMachine by BroadGun Software
TP1
Freq. Adj.
Ref. Mod. Adj.
VCO Mod. Adj.
TX VCO Adj.
RX VCO Adj.
Driver Bias
TX PA Bias
TX Pwr Cal.
Squelch level
TEST
POINTS

pdfMachine by BroadGun Software

pdfMachine by BroadGun Software

pdfMachine by BroadGun Software

pdfMachine by BroadGun Software

pdfMachine by BroadGun Software