Midland 91-1060-91-1110, 91-4050-91-4100, P25/FM Service Manual

SERVICE MANUAL ADDENDUM

P25/FM TWO-WAY

LAND MOBILE RADIO

BASE TECH III BASE/REPEATER

STATION

91-1060-91-1110 91-4050-91-4100

LOW CURRENT MODELS

VHF HIGH BAND

UHF BAND

Part Number: 680-100-2049

Revision A

1/12

Important Information

All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language without the written permission of Midland Radio Corporation.

No part of any copyrighted computer programs contained in the products referred to in this manual may be copied or reproduced without the express written consent of Midland Radio Corporation.

Midland Radio Corporation reserves the right to change the products described in this manual without prior notice.

This manual is designed to facilitate the set-up and service of the Midland 91-1060 / 1110 91-4050 / 91-4100 P25 Base Tech III series. As necessary, service manual supplements will be published and distributed on the following forms:

Manual Addition (MA) For supplemental information useful in product

service or improvement. Printed on BLUE paper.

Change Notice (CN) For details about changes made during

production by model and serial number. Printed on YELLOW paper.

Manual Correction (MC) For correcting literature errors not related to

production changes. Printed on GREEN paper.

Technical Bulletin (TB) For solutions to field problems and tips for

performance improvement. Printed on PINK paper.

Comments or suggestions concerning areas of manual improvemen t are welcome.

TABLE OF CONTENTS

Manual Supplement Information ii Table of Contents iii Acronyms and Abbreviations iv

GENERAL INFORMATION

Specifications 1-2 Accessories 3-4

PREPARATION

Alignment 5-12

CIRCUIT DESCRIPTION

Description 13-18

DIAGRAMS

VHF/ UHF General Block Diagrams 19-22 Front Panel Unit Schematic 23 Analog Logic Unit Schematic 24 VHF RX Main Unit Schematic 25 VHF RX VCO Unit Schematic 26 VHF TX Main Unit Schematic 27 UHF RX Main Unit Schematic 28 UHF RX VCO Unit Schematic 29 UHF TX Main Unit Schematic 30 Front Panel Unit Layout 31 Analog Logic Unit Layout 32 VHF RX Main Unit Layouts 33 VHF RX VCO Unit Layout 33 VHF TX Main Unit Layouts 34 UHF RX Main Unit Layouts 35 UHF RX VCO Unit Layout 35 UHF TX Main Unit Layouts 36 Chassis Exploded View 37 Palm Microphone Schematic 39

PARTS

Low Current Specific Parts List…………….. 40-56 Replacement Parts Ordering 57

ACRONYMS AND ABBREVIATIONS

Below is a list of common electrical abbreviations used in documentation.

CTCSS --------------------- Continuous Tone-Controlled Squelch System DCS (or CDCSS) --------- Continuous Digital-Controlled Squelch System EEPROM ------------------ Electrically Erasable Programmable Read Only

Memory MIL SPEC ------------------ Military Specification RX --------------------------- Receive TX --------------------------- Transmit SINAD ---------------------- The ratio in decibels of signal + noise +

distortion to noise + distortion VCO ------------------------ Voltage Controlled Oscillator TCXO ---------------------- Temperature Compensated Crystal Oscillator PLL ------------------------- Phase Locked Loop

General Information

SPECIFICATIONS -VHF

General

Frequency Range: A Band: 136-156 MHz, B Band: 146-174 MHz Number of Channels: 500 channels with name, 10 groups of 50 channels Channel Spacing: FM 12.5 / 20 / 25 / 30 kHz Digital C4FM Operation Mode: Simplex / Duplex / Full Duplex/ Repeat Antenna Impedance: 50 ohm unbalanced Power Supply: DC 13.6 V, negative ground only Consumption: <120mA Standby @RX ~1 A @TX ≤ 12 A (60W), ≤ 20 A (110W) Environmental Conditions: -30 to +60 degrees C, 95% humidity @ 35C Dimensions: 18.2” (w) x 3.4” (h) x 14.2” (d), (462 mm x 88 mm x 360 mm) Weight: 24 lbs (11 kgs)

Transmitter

Output Power: (91-1060) 25-60 W, continuous

(91-1110) 5-110 W, continuous

Switchable Bandwidth: Full Sub Band Maximum Deviation: ± 5kHz (wide band), ± 2.5 kHz (narrow band) Frequency Stability: ≤1.5 ppm std, 10 MHz external optional Frequency Response: +1 dB / -3 dB, 300-3000 Hz, 1 kHz reference FM Hum and Noise: ≤ 50 dB @1kHz 70% mod., ≤ 50 dB Digital mode Modulation Distortion: ≤ 3% Spurious & Harmonics: ≤ 0.25µW (≥ 80 dBc)

Receiver

Switchable Bandwidth: Full Sub Band IF Frequencies: 1 Frequency Stability: ≤1.5 ppm Sensitivity: ≤ 0.40 µV @ 20 dB N.Q., ≤ 0.30 µV @ 12 dB SINAD ≤ 0.30µV, Digital 5% BER Squelch Sensitivity: ≤ 0.25 µV Selectivity: ≥ 85 dB @ 25 kHz, ≥ 80 dB @ 12.5 kHz (TIA-603) ≥ 80 dB Digital Intermodulation: ≥ 85 dB Spurious Response: ≥ 100 dB AF Response: +1 / -3 dB, 300-3000 Hz, 1 kHz reference AF Distortion: ≤ 3% @ 1 kHz 60% mod.

Audio Output Power: 7.5 Watts @ 8 Ώ/ 10 Watts @ 4 Ώ

Signal to Noise Ratio: ≥ 50 dB @ 1 kHz 70% mod. (wideband), ≥ 45 dB (narrowband)

IF: 48.4 MHz, 2nd IF: 455 kHz

Low Current Base Tech 3.5

General Information

Low Current Base Tech 3.5

SPECIFICATIONS -UHF

General

Frequency Range: A Band: 400-435 MHz, B Band: 440-475 MHz

C Band: 465-500 MHz, D Band: 485-520 MHz

Number of Channels: 500 channels with name, 10 groups of 50 channels Channel Spacing: FM 12.5 / 20 / 25 / 30 kHz; Digital C4FM Operation Mode: Simplex / Duplex / Full Duplex/ Repeat Antenna Impedance: 50 ohm unbalanced Power Supply: DC 13.6 V negative ground only

Consumption: <120mA Standby @RX ~1 A

@TX ≤ 12 A (60W), ≤ 20 A (110W) Environmental Conditions: -30 to +60 degrees C, 95% humidity @ 35C Dimensions: 462 mm (w) x 88 mm (h) x 360 mm (d); 18.2” x 3.4” x 14.2” Weight: 11 kg (24 lbs.)

Transmitter

Output Power: (91-4050) 25-50W continuous

(91-4100) 2-100W continuous

Switchable Bandwidth: Full sub band Maximum Deviation: ± 5 kHz (wide band); ± 2.5 kHz (narrow band) Frequency Stability: ≤1.5 ppm std, 10 MHz external optional Frequency Response: Within +1, -3dB, 300-3000Hz FM Hum and Noise: ≥ 50 dB @1 kHz 60% mod.; ≥ 50 dB Digital Modulation Distortion: ≤ 3% Spurious & Harmonics: ≤ 0.25 µW (-80 dBc)

Receiver

Switchable Bandwidth: Full sub band IF Frequencies: 1 Frequency Stability: ≤1.5 ppm Sensitivity: ≤ 0.40 µV for 20 dB N.Q./ ≤ 0.30 µV for 12 dB SINAD < 0.30 µV Digital 5% BER Squelch Sensitivity: ≤ 0.25 µV Selectivity: ≥ 85 dB @ 25 kHz; ≥ 80 dB @ 12.5 kHz (TIA-603);

Intermodulation: ≥ 85 dB Spurious Response: ≥ 100 dB AF Response: +1 / -3 dB, 300-3000 Hz, 1 kHz ref. AF Distortion: ≤ 3% @ 1 kHz 60% mod. Audio Output (<2% distortion): 7.5 Watts @ 8 Ώ/ 10 Watts @ 4 Ώ Signal to Noise Ratio: ≥ 50 dB @ 1kHz 60% mod. (45 dB at narrow)

IF: 73.35 MHz, 2nd IF: 455 kHz

≥ 80 dB Digital mode

General Information

OPTIONS & ACCESSORIES

71-7220B 30 AMP Rack-mount Power Supply 220/110VAC

71-1230BM Battery Back-up Module for 7220B

71-0033 DC Power Cable, 48”

71-7801 External TX/RX Antenna Relay (Up to 400 Watts)

71-7751 Internal TX/RX Antenna Relay

71-8820D 31-1/2” Indoor Cabinet, complete with locking doors

71-8830D 40-1/4” Indoor Cabinet, complete with locking doors

71-8082 Slide Rails for TX/RX Unit

Low Current Base Tech 3.5

71-8834 Hardware Kit for Cabinets

71-8822-2AS Grounding Kit for 31-½” Cabinets

71-8822-2AT Grounding Kit for 40-1/4” Cabinets

71-8871 12-1/4” Blank Panel

71-8870 10-1/2” Blank Panel

71-8863 3-1/2” Blank Panel

71-8862 1-3/4” Blank Panel

91-1303B USB Programming Cable

91-1480CD Base Tech III Programming Software

71-2020E 16 Channel Tone Remote Termination

71-2022E E&M Expansion Kit used with 71-2020E in

71-8885A/D Option Shelf (only)

71-8885A Option Shelf with Slides / Easy Access & AC Supply

No Battery Charge

General Information

Low Current Base Tech 3.5

71-8885AC Option Shelf with Slides / Easy Access & AC Supply

with Battery Charge

71-8885D Option Shelf with Slides / Easy Access & DC

Operation

71-7206 Tone Termination Lightning / Surge Protection

(2wire / 4-wire)

71-7207 AC Surge Protection Kit (115V only)

71-7655A RF Line Surge Protection

71-8880 90” Aluminum Rack

71-8881 Shipping Hardware Kit, 71-8880

71-8879 Radio Shelf Support Kit (Relay Racks Only)

71-2315 Palm Microphone

71-2316 Desktop Microphone

71-8155-1 VHF Duplexer (3-5MHz Separation) 350W, 150-160

MHz

71-8155-2 VHF Duplexer (3-5 MHz Separation) 350W, 160-174

MHz

71-8152-3 VHF Duplexer (2 MHz Separation) 350W, 150-160

MHz

71-8152-4 VHF Duplexer (2 MHz Separation) 350W, 160-174

MHz

71-8455A UHF Duplexer (3-5 MHz Separation) 350W, 440-

512 MHz

71-8455D UHF Duplexer (3-5 MHz Separation) 350W, 406-

430 MHz

Alignment Procedures

Low Current Base Tech 3.5

THIS PAGE INTENTIONALLY LEFT BLANK

Alignment Procedures

Low Current Base Tech 3.5

RECEIVER (RX MAIN UNIT)

1. Pre-selector and Post-selector Tuning

Both selectors have been pre-tuned at the factory, so no alignment is require d.

2. FVR001 Tight Squelch Level

This potentiometer allows adjustment to the tight squelch level.

3. FVR002 De-mod out Bias Level

This potentiometer allows adjustment to the level of DC Bias on the De-Mod output.

4. L303 VCO Alignment

The VCO has been aligned at the factory to cover full sub-band. However, if you need to re-adjust VCO after a repair, set the VCO voltage to 10.5 V at the highest end of the sub b and using L303. The VCO cover must be removed for access. Note that tuning slug may be glued and breakage could occur.

5. RX 0-dBm Level Adjustment

This is 600 ohm audio available on pins 20 and 21 of the EXT Option port. It is electronically a djuste d. Ground TP-2 on the Analog Logic Unit PCB, and power-up the radio. See Figure 3 on page 6. The station is now in Adjust Mode. Release TP-2 from ground. The di splay should look as follows:

RXNS <Adjust> TXN RX 0dbm Out C0001 27 / 31 AA

Use the “A” and “B” keys on the front panel to adjust the level up or down. Pressing the “#” key will change the mode you are adjusting. The “A” key will increase the level while the “B” key will decrease the level. You will be able to monitor the output if the station is recei v ing a valid carrier and signaling. Cycle power to the radio to return to normal operation. NOTE: The other ADJUST Modes are in order of appearance:

RX 0 dbm REPEA T DE VI DIGITAL DEVI ANALOG DEVI TONE DEVI CTC DEVI WID CTC DEVI NRW

FVR002

De-mod Bias

FVR001

Tight Squelch

Alignment Procedures

Low Current Base Tech 3.5

Figure 1: Receive Module (RX Main Unit) Alignment Adjustment s

Alignment Procedures

Low Current Base Tech 3.5

EXCITER (TX MAIN UNIT)

1) FVR201 Sub-Audible Modu lation Balance

This potentiometer sets modulation balance below 300 Hz. Carefully align this potentiometer to obt ain flat deviation from the lowest to the highest frequency programmed in the transmitter.

2) FVR202 Sub-Audible Modu lation Deviation

This potentiometer determines low frequency (below 300Hz) deviation. When POCSAG an d DCS are

used, it may be necessary to readjust to have enough deviation and fidelity at lower frequencies.

FVR201 and FVR202 are used together to adjust amplitude and fidelity of square wave output of the

transmitter in Analog Mode.

3) FVR203 Carrier Frequency Trim

This potentiometer adjusts carrier frequency. Its range will allow for +/- 200 Hz adjustment from the desired (programmed) frequency.

4) FVR204 Exciter Output Power

This potentiometer adjusts the exciter’s output power level. This is nominally 80 mW.

5) L303 VCO Alignment

The VCO has already been aligned at the factory. However, if you need to re-adjust VCO af ter a rep air, set the VCO voltage to 10.5 V at TP301 at the highest end of the sub band using L303.. This p art can be found beneath the cover. See Figure 2. Note that tuning slug may be glued and breakage could

occur.

VCO L303

FVR204

Output Power

(under cover)

TP301)

FVR203

Frequency Trim

FVR201

Sub-Audible

Balance

FVR202

Sub-Audible

Deviation

Figure 2: Exciter Module (TX Main Unit) Alignment Adjustments

6) Electronic Transmitter Alignment

The station must first be put into “Adjust Mode.”

Figure 3: Entering Alignment Adjust Mode

Entering & Exiting Alignment Adjustment Mode a) If not already, power off the radio.

Alignment Procedures

Low Current Base Tech 3.5

TP2

lignment Mode

b) Terminate the radio TX port into a 50 ohm load rated for at least 150 Watts. c) Place the Local / Remote Switch (on the front panel of the 71-8885 Deluxe Option Housing if

equipped) into the Local position. d) Ground TP2 on the Analog Logic Unit PCB (the nearby PA Unit chassis is a good ground point.) e) Apply power to the radio. The radio should power-on directly into the Adjust mode (indicated by

“<Adjust>” displayed on-screen.) If the radio displays an error message on the fourth line of the

LCD, check that the Local / Remote Switch is in the Local position. f) Open the ground connection to TP2. g) When the desired alignment procedures have been conducted, remove powe r from the radio to exit

the adjustment mode. Changes made during alignment will be a utomatically stored when e ntered. h) The following adjustment are available in order of appearance:

RX 0 dbm

REPEA T DE VI

DIGITAL DEVI

ANALOG DEVI

TONE DEVI

CTC DEVI WID

CTC DEVI NRW

Alignment Procedures

Low Current Base Tech 3.5

8) Maximum Analog Deviation Limiting Alignment (Base Station and Repeater) a) Press the “#” key on the Front Panel until second line of the LCD displays “ANALOG DEVI.” b) Apply a 1 kHz tone at the microphone input at a level required to obtain 60% system deviation. Use

pins 1 and 2 (pin 2 = ground). c) Activate PTT by grounding pin 4 of the microphone jack. Note the audio generator level setting. d) Increase the audio level by 20 dB (equivalent to 10x voltage increase). e) Press the “A” key to increa se or the “B” key to decrease the system deviation until it is just below

±4.5 kHz without CTCSS modulation or ±4.7 kHz with CTCSS modulation (25 / 30 kHz channel

spacing) or ±2.3 kHz without CTCSS modulation or ±2.5 kHz with CTCSS modulation (12.5 / 15

kHz channel spacing). The radio is in limiting at this point, so distortion will be higher according to

the service monitor. Deviation should be measured with at least a 50 Hz to 15 kHz filter enabled (no

higher than 20 kHz). f) Deactivate the transmitter.

9) Analog Repeater Deviation Alignment (This should be checked AFTE R St ep 8 has been accomplished) a) Press the “#” key on the Front Panel until second line of the LCD displays “REPEAT DEVI.” b) Set the radio to a channel programmed for repeat mode (wide or narrow band). c) Inject a -47 dBm ± 3 dB RF signal modulated with a 1 kHz tone into the receiver input at 60%

system deviation. Enable sub-audible signaling if the radio (repeater) is configured as so. d) At this time, the radio (repeater) should be transmitting. e) Measure the transmitter deviation level. Enable audio filtering of 300 Hz to 3 kHz if sub-audio

signaling is present. If sub-audio signaling can not be filtered, set the radio to a channel

programmed without sub-audio signaling enabled, and disable sub-audible signaling on the signal

source. f) Press the “A” key to increase or the “B” key to decrease the repeater transmitter deviation until it is

60% ± 5% system deviation. g) Remove the RF signal.

10) Analog CWID/DTMF Deviation Alignment a) To best perform this alignment, it is preferred to program a radio channel to the desired operational

parameters intended for daily operation. It is typical that this channel is to also transmit the normal CWID tone sequence. If no channel has been programmed as described, continue with the

remaining steps. b) Press the “#” key on the Front Panel until second line of the LCD displays “TONE DEVI.” c) Activate PTT. d) Press the “A” key to increa se or the “B” key to decrease the CWID transmitter deviation until it is

40% ± 5% system deviation. e) Deactivate PTT.

Alignment Procedures

Low Current Base Tech 3.5

11) CTCSS Deviation Alignment a) Press the “#” key on the Front Panel unti l the second line of the LCD displays “CTC DEVI WID.” b) Activate PTT. c) While monitoring peak FM deviation, adjust the deviation level to obtain 500 Hz ± 10 Hz positive

and negative peak deviation. Enable audio filtering below 300 Hz only. Press the “A” key to

increase or the “B” key to decrease the transmitter wideband CTCSS deviation level. d) Deactivate PTT. e) . Press the “#” key on the Front Panel until the second line of the LCD displays “CTC DEVI NRW. f) Activate PTT. g) While monitoring peak FM deviation, adjust the deviation level to obtain 250 Hz ± 10 Hz positive

and negative peak deviation. Enable audio filtering below 300 Hz only . Press the “A” key to increase

or the “B” key to decrease the transmitter narrowband CTCSS deviation level.

h) Deactivate PTT.

12) C4FM Digital Deviation Alignment a) Press the “#” key on the Front Panel unti l the second line of the LCD displays “DIGITAL DEVI.” b) Activate PTT. c) While monitoring peak FM deviation, adjust the deviation level to obtain 2827 Hz ± 283 Hz positive

and negative peak deviation. Press the “A” key to increase or the “B” key to decrease the

transmitter C4FM digital deviation level. d) Deactivate PTT. e) Exit alignment mode by cycling power to the radio. f) After radio reset is complete, press the Shift key followed by the numbe r 0 key. g) Press the number 2 key to transmit the Standard Transmitter Sym bol Rate Pattern. h) Activate PTT. i) Monitor peak FM deviation. Verify that both positive and negative peak deviation levels each fall

within 2544 Hz to 3111 Hz deviation. j) Press the number 3 key to transmit the Standard Transmitter Low Deviation Pattern. k) Monitor peak FM deviation. V erify that both positive and negative peak deviation levels each fall

within 848 Hz to 1037 Hz deviation.

l) Deactivate PTT.

Alignment Procedures

Low Current Base Tech 3.5

FRONT PANEL UNIT

1) VR40

2) F

1 Alignment This is to set volume level by pulse code switch. Press on Press again, and the backlight lighting level can be se Press a third time, and the backlight timer ca

n be set.

VR401 Transmitter Hi-Power Alignment

ce and Noise Squelch can be set.

This potentiometer allows for fine adjustment of the High-Power level of the transmitter output whe n the radio is set to High-Power Mode. S tation will indicate

in the right side of the display when in

High-Power Mode. Press “SHIFT,” then “2” to toggle transmitter Power Mode.

Note: “TX Power Change” MUST be enabled in software programming to toggle TX Power from the Front Panel.

3) FVR402 Transmitter Low-Power Alignment This potentiometer allows for fine adjustment of the Low-Power level of the transmitter output when the radio is set to Low-Power Mode. The station must be on a low-power channel, or the station must be placed in the Low-Power Mode. Press “SHIFT,” then “2” to toggle transmitter Power Mode.

FVR402

Low-Power Level

djustment

FVR401

High-Power Level

djustment

VR401

itchPulse Code Sw

Function by # of presses:

1. Volume

2. Noise Squelch

3. Backlight Dim

4. Backlight Timer

Circuit Description

Low Current Base Tech 3.5

LOW CURRENT IMPROVEMENTS

In order to improve standby current consumption the Receiver Unit, Transmitter Unit, Analog Logic Unit and

Front Panel Unit have been modified from the original Base Tech III configuration. These improvements will

start to be incorporated into all Base Tech III radios manufactured in 2012. Earlier versions of Receiver Unit,

Transmitter Unit and Analog Logic boards should not be mixed. RF Power Amplifiers remain unchanged. A

label marked “Low Current Variant” will be affixed to all receiver, transmitter, analog logic and front panel

units for easy identification. The Front Panel Unit may be used with either standard or Low Current models.

RECEIVER UNIT

1) RF Section

An incoming signal is fed to the pre-selector bandpass filter and amplified by Q861. It is then fed to the

post-selector bandpass filter. The balanced mixer, consisting of IC811, produces the first IF (VHF =

48.5 MHz/ UHF = 73.35 MHz) by injection from the 1

2) IF Section

The first IF signal is fed to crystal filter, XF801, then amplified by Q810. Again, this signal is fed to the

4-pole crystal filters and amplified by Q001. Following amplification, the signal is fed to the 2

processor (IC001). The 2

signal (455 kHz). IC001 amplifies the 2

local oscillator (crystal) signal is directed to IC001 to produce the 2nd local IF

local IF signal, which then becomes an audio baseband signal

local oscillator generated by RX VCO.

through a detector circuit internal to IC001. This audio signal is then directed to the low pass filter

inclusive within IC002, after which it is sent to audio processor, IC3.

3) VCO section

The oscillator circuit produces the 1

local oscillator signal

(VHF = RX frequency + 48.5 MHz / UHF = RX frequency – 73.35MHz).

The 1

local oscillator signal is amplified by buffer Q302, then amplified by pre-amplifier IC301 and

post-amplifier Q303. The amplified signal is fed to the first balanced mixer. The VCC for the VCO has

been changed from 7 volt s to 5 volts.

4) PLL Section

The PLL IC, IC806, with integrated pre-scaler compares the phase between the VCO frequency and

reference oscillator frequency (12.00 MHz) by method of dividing the frequency, and produces VCO

control signal. Then, this control signal is fed to the charge pump and fed to the low-pass-filter. The

supply voltage of charge pump is multiplied by IC807 (to approx. 13 V) to achieve greater S/N ratio.

5) Low Current Improvements

An additional 5.5 volt dc source has replaced the 12 V dc source for main on board power. An additional

12 volt line has been added for the 7 V dc regulator. This significantly reduces current consumption

losses to heat.

Circuit Description

Low Current Base Tech 3.5

EXCITER UNIT

1) VCO Section

The oscillator circuit generates transmitter frequency. Then this signal is fed to the 3-stage of amplifier,

buffer amplifier Q302, pre-amplifier IC301 and post amplifier Q303 and lead to the final amplifier, and

lead to the final amplifier.

2) PLL section

Basically, the circuit description is the same as RX. The PLL IC inclusive with prescaler (IC208)

compares the phase between VCO signal and reference oscillator frequency (12.00 MHz) by method of

dividing the frequency, and produces VCO control signal. Then this VCO control signal is fed to the

charge pump, and fed to the low-pass-filter. The supply voltage of charge pump is amplified by IC210

(to approx. 13 V) to achieve greater S/N ratio.

3) Modulation Section

The modulation signal is fed to both VCO and the reference oscillator (TCVXO 12.00 MHz), this permits

very flat modulation characteristics against low frequency (DC). This is an advantage when BASE

TECH III is used as a POCSAG transmitter.

4) TX Exciter Section

The VCO signal is amplified by Q211 to achieve 80 mW.

5) Low Current Improvements

An additional 5.5 volt dc source has replaced the 12 V dc source for main on board power. An additional

12 volt line has been added for the 7 V dc regulator. This significantly reduces current consumption

losses to heat.

POWER AMPLIFIER

1) Power Amplifier (VHF = 5-110W/ UHF = 2-100W)

The 80 mW signal from TX Exciter stage is fed to PM501 to produce 10W output. Then, Q504 and Q505

amplify to 110/100W. This signal is fed to the Low-Pass- Filter to eliminate the harmonics and spurious

frequencies. An APC circuit formed by IC502 stabilizes the output power at the set level. An IC501

protects final stage transistors from the reverse power caused by a mismatched antenna system

2) Power Amplifier (VHF = 60W / UHF = 50W)

The 80 mW signal is fed to PM501 to achieve 60/50W output power. Then, signal is fed to the LPF to

eliminate the harmonics spurious frequencies. An APC circuit formed by IC502, IC503, Q504 and

Q505 stabilizes the output power at the set level. IC501 protects PM501 from the reverse power

caused by a mismatched antenna system

Circuit Description

Low Current Base Tech 3.5

DESCRIPTION OF CIRCUITS TO STABILIZE TX AND RX FREQUENCY

The transmitter and receiver each use a TCVXO (Temperature Compensated Voltage-Controlled Crystal

Oscillator) to generate the 12.00 MHz reference frequency used within their respective PLL and VCO

circuits. The accuracy of the TCVXO is better than +/- 0.00015% over the range of –30 degree C to +60

degree C.

DESCRIPTION OF CIRCUIT TO SUPPRESS SPURIOUS EMMISSIONS AND MODULATION LIMITING

A multiple pole Low Pass Filter is used after the final power amplifier stage. It is designed to sharply

attenuate spurious and harmonics frequencies above the highest frequency in the sub-band of the radio.

Modulation limiting is performed by TX audio processor, CMX7041L4, located on the Analog Logic Unit.

Internal limiting/compression amplifier provides excellent limiting with minimum distortion.

In addition to modulation limiting, this device contains all circuitry to perform pre-emphasis, band pass

shaping and CTCSS/ DCS encoder.

ANALOG LOGIC UNIT

1) Microcomputer (CPU) Section

CPU IC1, H8S2239 is the 16-bit processor contained 320kb flash memory 6k RAM inside. The CPU

controls all functions of Base Tech III. A flash memory permits on-board-up-grade when new firmware

is released.

2) EEROM Section

IC6 is the 64k bit EEROM. This memory contains all the channel data

3) Audio Processor Section

IC2 is for TX and IC3 is for RX audio processors. CTCSS and DCS are processed within these audio

processors. In previous releases the CTCSS and DCS were processed within separate processors.

This also improves current consumption and simplifies the sub-signaling routines.

4) Low Current Improvements

A DC-DC converter (IC 43) has been added to replace the analog 12 volt to 5 volt regulator (IC5).

The DC to Dc converter runs at 170kHz and directly regulates 5.5 volts with no losses to heat

dissipation. This significantly reduces overall current consumption.

DIGITAL LOGIC UNIT (DSP)

IC1 acts as the DSP control for both incoming digital signal converting it to analog and analog

signal to C4FM digital signal. External flash memory within IC2, has 4Mb capacity, contains all

data. Program data is stored in 256 k-bytes of memory integrated within IC1.

+ 43 hidden pages

Midland 91-1060-91-1110, 91-4050-91-4100, P25/FM Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual