Kenwood TK-280 User manual

VHF FM TRANSCEIVER
TK-280
©1999-4 PRINTED IN JAPAN
B51-8454-10(S) 1217
SERVICE MANUAL
GENERAL ................................................................................. 2
SYSTEM SET-UP ..................................................................... 2
OPERATING FEATURES ......................................................... 3
REALIGNMENT ...................................................................... 11
CIRCUIT DESCRIPTION ........................................................ 16
SEMICONDUCTOR DATA ..................................................... 22
DESCRIPTION OF COMPONENTS ....................................... 27
PARTS LIST............................................................................ 28
EXPLODED VIEW .................................................................. 34
PACKING ................................................................................ 35
ADJUSTMENT ........................................................................ 36
TERMINAL FUNCTION .......................................................... 44
PC BOARD VIEWS
DISPLAY UNIT (X54-3210-XX) ........................................... 45
TX-RX UNIT (X57-5740-XX) ............................................... 51
SCHEMATIC DIAGRAM ......................................................... 57
BLOCK DIAGRAM .................................................................. 61
LEVEL DIAGRAM ................................................................... 63
OPTINONS ............................................................................. 64
SPECIFICATIONS ...............................................BACK COVER
CONTENTS
CAUTION
When using an external power connector,
please use with maximum final module
protection of 9V.
Photo is K3 type with KRA-14
Knob (ENC)
(K29-5232-03)
Knob (VOL)
(K29-5231-03)
Cabinet assy
(A02-2054-53)
:K,K2,M (4 keys)
(A02-2055-53)
:K3,K4 (16 keys)
Badge
(B43-1106-14)
Packing
(G53-0840-02):K,K2,M (4 keys)
(G53-0841-02):K3,K4 (16 keys)
Panel assy
(A62-0535-04)
Knob (PTT etc)
(K29-5157-03)
Helical antenna
(T90-0679-05):M
This service manual is same at the TK-280(B51-8454-00)
service manual with destination K, K3 and M with the
exception of new destination, K2 and K4.
REVISED

TK-280
2
GENERAL / SYSTEM SET-UP
INTRODUCTION
SCOPE OF THIS MANUAL
This manual is intended for use by experienced technicians
familiar with similar types of commercial grade communications
equipment. It contains all required service information for the
equipment and is current as of the publication data. Changes
which may occur after publication are covered by either Service
Bulletins or Manual Revisions. These are issued as required.
ORDERING REPLACEMENT PARTS
When ordering replacement parts or equipment information,
the full part identification number should be included. This
applies to all parts : components, kits, or chassis. If the part
number is not known, include the chassis or kit number of which
it is a part, and a sufficient description of the required
component for proper identification.
PERSONNEL SAFETY
The following precautions are recommended for personnel
safety:
●DO NOT transmit until all RF connectors are verified secure
and any open connectors are properly terminated.
●SHUT OFF and DO NOT operate this equipment near
electrical blasting caps or in an explosive atmosphere.
●This equipment should be serviced by a qualified technician
only.
SERVICE
This radio is designed for easy servicing. Refer to the
schematic diagrams, printed circuit board views, and alignment
procedures contained within.
NOTE
WE CANNOT guarantee oscillator stability when using
channel element manufactured by other than KENWOOD or
its authorized agents.
FCC COMPLIANCE AND TYPE NUMBERS
Type Type acceptance number Frequency range Compliance
K,K3 ALH24613110 146~174MHz Parts 22,74,80,90
K2,K4 ALH24613120 136~162MHz Parts 22,74,80,90
Unit X57-5740-XX X54-3210-XX
Model & Frequency range Remarks QT/DQT DTMF Charger Battery 16 Keys
destination 0-10 0-11 0-10 0-11
K, M __ 146~174MHz _–OP OP –
TK-280 K3 __ IF1 : 44.85MHz __
K2 __ 136~162MHz LOC : 44.395MHz _–OP OP –
K4 __ _ _
Merchandise received
License and frequency allocated by FCC
Choose the type of transceiver
Transceiver programming
Delivery
Are you using the speaker microphone?
TX/RX 146~174 5.0W TK-280 K,K3,M
TX/RX 136~162 TK-280 K2,K4
Frequency range (MHz) RF power Type
A personal computer (IBM PC or compatible), programming
interface (KPG-36), and programming software (KPG-49D)
are required for programming.
(The frequency, trunked system features, conventional system
features, TX power HI/LOW, and signalling data are programmed
for the transceiver.)
YES
NO
KMC-25
Speaker microphone
(Option)
SYSTEM SET-UP

TK-280
3
OPERATING FEATURES
1. Operation Features
The TK-280 is an VHF FM radio designed to operate in
both trunking format and conventional format. The
programmable features are summarized.
Model Trunking Format Trunking mode
Conventional Format Conventional mode
■Trunking Format
This format can handle up to 32 systems with up to 250
groups in each system. The transceiver can be used in both
trunked mode and conventional mode. Systems, groups,
and their functions are programmed.
■Conventional Format
This format can handle up to 250 groups with 250 channels
in each group.
The transceiver can be used only in conventional mode.
Groups, channels, and their functions are programmed.
2. Transceiver Controls and Indicators
2-1. Physical Layout
Note: The transceiver is also available without the DTMF
keypad (-).
2-2. Panel controls
The key on the top and front panel is momentary-type push
buttons. The functions of these keys and knob are explained
below.
1Antenna connector
Connect the supplied antenna here.
2System or Group selector knob (Programmable)
●Trunking Format
Turning the system (or group) selector knob clockwise
increases the system (or group) number by one. Turning
the knob in the counterclockwise direction decreases the
system (or group) number by one.
After the system number (or group number) reaches the
highest system number (or group number), it goes back to
lowest system number (or group number).
System numbers (or group numbers) not set are skipped.
Caution : The FPU (KPG-49D) allows selecting between
system selector and group selector.
●Conventional Format
Turning the group (or channel) selector knob clockwise
increases the group (or channel) number by one. Turning
the knob in the counterclockwise direction decreases the
group (or channel) number by one.
After the group number (or channel number) reaches the
highest group number (or channel number), it goes back to
lowest group number (or channel number).
Group numbers (or channel numbers) not set are skipped.
Caution : The FPU (KPG-49D) allows selecting between
group selector and channel selector.
3Volume/Power switch
●Trunking Format
Transceiver Power and Volume switch. Turn clockwise to
switch On the transceiver. Turn counterclockwise fully to
switch OFF the transceiver. Also adjusts the volume level.
When the power is switched off, all the parameters, such
as the system and group, are stored in memory. When the
power is switched on again, the system returns to the
previous conditions.
●Conventional Format
Transceiver Power and Volume switch. Turn clockwise to
switch On the transceiver. Turn counterclockwise fully to
switch OFF the transceiver. Also adjusts the volume level.
When the power is switched off, all the parameters, such
as the group and channel, are stored in memory. When the
power is switched on again, the group returns to the previous
conditions.
4Auxiliary (orange) key (Programmable)
5Battery pack release catch
Push down to release the battery pack. See Installing the
Ni-Cd Battery Pack.
6MONITOR key* (Programmable)
7PTT (Push-To-Talk) key
Press this key, then speak into the microphone to call a
station.
8LAMP key* (Programmable)
9TX/BATT indicator
This red LED lights during transmission (it does not light
during busy or when transmit is prohibited). If the battery
voltage falls below the programmed voltage during
transmission, the brightness of this indicator decreases at
intervals of about one second, so it can be used as the
battery voltage alert function.

TK-280
4
OPERATING FEATURES
0S, A, 2B, and C 3key (Programmable)
-DTMF keypad (keypad model only)
Press the keys on the telephone keypad to send DTMF
tones.
=Universal connector
Connect the external KMC-25 speaker/ microphone
(optional) here. Otherwise, keep the supplied cover in place.
* : MONITOR and LAMP are arbitrary names chosen for
these buttons. They can be used for any of the auxiliary
functions.
2-3. Programmable keys
The FPU (KPG-49D) enables programmable keys to select
the following functions.
■Trunking Format
Auto Tel, AUX(only when Voice Scrambler is not selected),
Connect ID, Disconnect ID, Display Character, Emergency
(only AUX key), Function, Group Down, Group Up, Home
Group, Key Lock, Lamp, Memory (RCL/STO), Memory (RCL),
Memory (STO), Monitor A, Monitor B, Monitor C, Monitor D,
Redial, RF Power Lo, Scan, Scan Del/Add, Scan Temporary
Delete, Scrambler (Only when Voice Scrambler is selected),
System Down, System Up, TEL Disconnect and none.
■Conventional Format
AUX(only when Voice Scrambler is not selected), Channel
Down, Channel UP, Connect ID, Disconnect ID, Display
Character, Emergency (only AUX key), Function, Group Down,
Group Up, Home Channel, Key Lock, Lamp, Memory (RCL/
STO), Memory (RCL), Memory (STO), Monitor A, Monitor B,
Monitor C, Monitor D, Operator Selectable Tone, Redial, RF
Power Lo, Scan, Scan Del/Add, Scrambler (Only when Voice
Scrambler is selected), Talk Around and none.
These functions the FPU programs to the function keys are
described in the following sections.
1) Auto TEL (Trunking Format)
Automatically connects available repeaters that are
connected to telephone circuits when operating as LTR
system. The time allocated to search for available repeaters
is 60 seconds, after which connection failure occurs, a DTMF
tone is output and the function terminates.
If connection to an available circuit is made, only ID 253,
EOT or hang-up time-out can terminate the function.
2) AUX
This function can be programmed when the voice scrambler
board is not installed.
If this key is pressed, an underscore (“_”) appears at the
extreme right of the LCD and AUX port which is inside of
the transceiver turns to the active level. If pressed again,
the underscore disappears and the AUX ports turns to the
deactive level.
3) Channel up/down (Conventional Format)
When the key is pressed each time, the channel number to
be selected is incremented/decremented and repeats if held
for one second or longer.
This key works as the voice scrambler code selector in the
voice scrambler code select mode.
4) Connect ID
Pressing this key in Conventional mode, automatically sends
the preset Connect ID.
5) Disconnect ID
Pressing this key in Conventional mode, automatically sends
the preset Disconnect ID.
6) Display character
●Trunking Format
This key switches the LCD display between the system/
group number and system/group name.
●Conventinal Format
This key switches the LCD display between the group/
channel number and group/channel name.
7) Emergency
●Trunking Format
Pressing this key for longer than the programmed
“Emergency Key Delay Time” causes the transceiver to enter
the emergency mode. The transceiver jumps to the
programmed “Emergency System/Group” and transmits for
the programmed “Active Time”.
The transceiver disables mic mute while transmitting. After
finishing transmission, the transceiver receivers for the
programmed “Interval Time”. The transceiver mutes the
speaker while receiving. Following the above sequence, the
transceiver continues to transmit and receive.
●Conventinal Format
Pressing this key for longer than the programmed
“Emergency Key Delay Time” causes the transceiver to enter
the emergency mode. The transceiver jumps to the
programmed “Emergency Group/Channel” and transmits for
the programmed “Active Time”.
The transceiver disables mic mute while transmitting. After
finishing transmission, the transceiver receivers for the
programmed “Interval Time”. The transceiver mutes the
speaker while receiving. Following the above sequence, the
transceiver continues to transmit and receive.
8) Function
Pressing this key causes the transceiver to display “FCN”.
Then, pressing a DTMF key causes the corresponding
programmed function to start. This key may be convenient
when using many functions with the 12-key keypad (K3, K4
type).

TK-280
5
OPERATING FEATURES
9) Group up/down
When the key is pressed each time, the group number to
be selected is incremented/decremented and repeats if held
for one second or longer. In Conventional format, this key
works as the voice scrambler code selector in the voice
scrambler code select mode.
10) Home Channel (Conventional Format)
Press this key once, the channel switches to the pre-
programmed home channel.
11) Home group (Trunking Format)
Each pressing of the key selects a preset system/group.
12) Key lock
Pressing this key causes the transceiver to accept entry of
only the [Function], [Key Lock], [PTT], [Lamp], [Monitor A],
[Monitor B], [Monitor C], [Monitor D], and [Emergency] keys.
The locked keys also include the tuning control.
13) Lamp
This key illuminates the LCD and keys on the front panel.
When the key is pressed, the LED lamp goes on.
When it is released, the lamp goes off after about five
seconds. If any key is pressed while the LED lamp is on,
the lamp is kept on for five seconds.
14) Memory
This key allows DTMF memory data to be recalled; up to 32
memories each with a memory dial of up to 16 digits
and an A/N of up to 10 digits per memory.
15) Monitor
Used to release signalling or squelch when operating as a
conventional. It is also used to reset option signalling.
16) Operator Selectable Tone (Conventional Format)
This key switches the pre-set decode QT/DQT and encode
QT/DQT to OST (Operator Selectable Tone) tone pair.
Press this key, the transceiver enters to OST select mode.
In this mode, the display shows “OFF” and the operator can
select one of the OST tone pair using the tuning control.
The display shows “TONE ∗∗” and tone pair No. ∗∗ is
selected.
Press OST key again, the transceiver exits from the OST
select mode, and returns to the group/channel mode with
the handset indicator ( ) means that the OST tone pair is
selected. OST tone pair number or OFF can be memorized
for each channel.
16 kinds of tone pair for OST can be programmed by KPG-
49D. OST is useful to access the repeater with same radio
frequency and different tone (QT/DQT).
17) Redial
Pressing this key when System/Group(trunking format),
Group/Channel (Conventional Format) is shown, displays the
previously transmitted DTMF code. Pressing [PTT] at this time,
transmits the code that is currently displayed.
18) RF power low
Used to temporarily switch transmission output to low power.
Turning the function on enables:
Hi→Low, Low→Low
Key states are backed up, except in the PC mode when
they are reset.
19) Scan
Press this key starts scanning. Pressing this key stops
scanning.
20) Scan Del/Add
●Trunking Format
Used to select whether system scan routines are used during
system scan. Each pressing of the key (to ON) toggles
between lockout and lock. The scan routine is started when
on lock. The DEL indicator flashes when the system is on
lockout.
●Conventinal Format
This key switches the currently displayed channel between
“Delete” and “Add”.
The “Add” channel contained in the scan sequence, and
“Delete” channel is not contained. In the scan mode, this
key switches the channel delete or add temporarily.
21) Scan temporary delete (Trunking Format)
This key is temporarily deleted a system being scanned. If
you press this key when scan is stopped (when a call is
being received from another station), the system is
temporarily deleted and scanning restarts.
This key operates even when “Scan Type” is set to “List
Type System Scan”.
22) Scrambler
If a scrambler code (1 to 4) has been set in the FPU, an
underscore (“_”) appears at the extreme right of the LCD
display when scrambler is active. Pressing this key changes
ON/OFF of scramble operation.
Holding this key down for 2 seconds sets Scramble Code
Select Mode
23) System up/down (Trunking Format)
When the key is pressed each time, the system number to
be selected is incremented/decremented and repeats if held
for one second or longer.
24) Talk Around (Conventional Format)
Press this key, the transceiver uses the receive frequency
and the tone for transmission.
The operator can call the other party directory (without
repeater). Press this key again, the talk around function goes
off.

TK-280
6
OPERATING FEATURES
25) Telephone disconnect (Trunking Format)
Pressing this key ends an RIC connection (disconnects the
telephone line).
26) None
Sounds error operation beep, and no action will occur.
Use this function when the transceiver is required to be more
simple operated.
2-4. Display
or scrambler ( _ ) function. The delete/add indicator shows
the systems locked out of the scanning sequence. Selective
call and scrambler are optional functions that can be
programmed.
●Conventinal Format
The twelve-character dot matrix alphanumeric display
shows the group and channel numbers. You can program
group and channel names with up to ten characters in place
of these numbers. The left display is used as an add
indicator (∞) and the right is used for the selective call (:+:)
or scrambler ( _ ) function. The add indicator shows the
channels unlocked out of the scanning sequence. Selective
call and scrambler are optional functions that can be
programmed.
3. Scan Operating
3-1. In Case of Trunking Format
1) System scan
System scan can be selected with the “Scan” key by
programming the scan feature. When the “Scan” key is pressed
and the “SCN”’ mark appears, scan mode in entered. Scanning
starts from the system following the currently displayed system.
When a call is received, scanning stops, and the system and
group are displayed.
When the system knob or programming key is touched
during scanning, the scan stops and the revert system or group
can be changed. Scanning resumes one second after the key
is released.
System Scan consists of the following 2 types.
●Fix system scan
All the set systems except locked-out ones are scanned. If
the DEL/ADD feature is assigned to the programmable key, it
can be controlled from the front panel.
●List type system scan
A scan list can be set for each system.
The list to be scanned can be changed by changing the
display system
If many system have been set, the scan speed can be
increased by narrowing the systems to be scanned with scan
lists.
2) System lockout
The system lockout feature is used to lock systems out of
the scan sequence, and can be selected by programming in
the following two ways:
●Fixed lockout
The system to be locked out is selected by programming.
When a locked system is selected, the Delete (3) indicator
appears on the left of the SYSTEM indicator. The revert system
is scanned even if it is locked out. If there is a locked system,
the Delete (3) indicator flashes during fixed scanning.
1Sub display
Displays the system, channel and group numbers. Also
displays various functions, such as TA.
2P (Priority) indicator
The P indicator ( P) appears when a selected channel is
programmed as priority, in conventional operation.
3MON (Monitor) indicator
The MON indicator appears when the button programmed
as MONITOR is pressed.
4SVC (Service) indicator
This icon is not used on this transceiver.
5SCN (Scan) indicator
The SCN indicator appears when using Scan mode.
6LO indicator
Appears when low power is selected.
7Handset indicator
The handset indicator ( ) appears when the selected group
is programmed as telephone IDs. (Trunking Format) In
Conventional Format, the handset indicator ( ) appears
when the OST tone pair is selected.
8MAIL indicator
This icon is not used on this transceiver.
9Alphanumeric display
●Trunking Format
The twelve-character dot matrix alphanumeric display
shows the system and group numbers. You can program
system and group names with up to ten characters in place
of these numbers. The left display is used as a delete
indicator (3) and the right is used for the selective call (:+:)
P
9

TK-280
7
OPERATING FEATURES
●User selectable lockout
If the scan lockout feature is programmed to a key, the user
can lock systems out of the scan sequence with the key. To
lock a system out of the scan sequence, press the key when
the system is displayed. The Delete (3) indicator is displayed
on the left of the SYSTEM indicator.
To unlock a system, select the system and press the key.
The Delete (3) indicator disappears to indicate that the system
has returned to the scan sequence. The revert system is
scanned even if it is locked out. If there a locked system, the
Delete (3) indicator flashes during fixed scanning. If all systems
are locked out, the scan stops and only the revert system is
received.
3) Drop-out delay time (Scan resume time)
If a call is received during scan, the scan stops. The scan
resume time can be programmed as 0 to 300 seconds in one-
second increments. The default value is 3 seconds.
4) Dwell time
The dwell time is the time after transmission ends until the
scan resumes in scan mode. It can be set 0 to 300 seconds by
programming. The default value is 3 seconds.
5) System/Group revert
System/Group revert can be programmed for one of the
following;
●Last called revert
The system or group changes to the revert system or group
when a call is received with the system or group being scanned.
●Last used revert
If a system/group call is received during scanning and the
PTT button is pressed for transmission and response within
the drop out delay time, the system or group is assigned as
the new revert system or group.
●Selected revert
If the system/group was changed while scanning, the newly
selected system/group.
6) Scan message wait
The time for staying with the home repeater that receives a
signal during system scan and monitoring data messages can
be programmed. If there is no signal from the home repeater,
the system is scanned for about 50ms. If there is a signal,
three data messages are monitored. Normally, three data
messages are monitored for each system, and it can be
increased in multiples of three data messages per line to up to
eight lines.
If the repeater data message indicates that there is no call,
data monitoring is terminated and the home repeater of the
next system is scanned.
7) Group scan operation
Group scan can be programmed for each group. In addition
to the ID codes of the selected group, the ID codes of the
other groups that are permitted for group scan are decoded.
(The two fixed ID and block decode codes are always decoded.)
If, during group scanning, a call is received with one of the
selectable group ID codes for which group scan is enabled,
the group display indicates the group number that the call came
in with. That group then becomes the new selected group.
Group scan resumes after the specified dropout delay time or
dwell time shared by the system scan elapses.
8) In Conventional system.
If QT or DQT is set for the channel, the channels, including
signalling, are scanned.
In case of the priority group is set in conventional system, if
a group scan (including group scan during a system scan)
temporarily stops (receiving) in a group that does not have
priority, a look back is performed to the priority group. Look
back is performed according to the look back time A and B
settings. If a call is received on the priority group, reception
immediately switches to the priority group.
3-2. In Case of Conventional Format
1) Scan types
●Single Group Scan
You can scan all valid (ADD) channels in the displayed group
that can be selected with the group selector.
●Multiple Group Scan
You can scan all valid (ADD) channels in the all valid (ADD)
group.
2) Scan Start Condition
One or more non-priority channels must be added to all
channels that can be scanned. The transceiver must be in
normal receive mode (PTT off).
When you activate the key programmed to the scan function,
the scan starts. The scan icon “SCN” lights and “-SCAN-” or
revert channel (programmable) is indicated on alphanumeric
display.
3) Scan Stop Condition
The scan stops temporarily if the following conditions are
satisfied.
1A carrier is detected, then signalling matches on channels
for which receive the signalling is set by the programming
software.
2A carrier is detected on the channel for which receiving
signalling is not set by the programming software or when
the monitor (signalling cancel) function is activated.
4) Scan Channel Types
1Priority channel is the most important channel for the scan,
and always detects a signal during scan and when the scan
stops temporarily.

TK-280
8
OPERATING FEATURES
2Non-priority channels detects a signal during scan. For the
channels that can be selected with the group or channel
selector when the scan does not occur, adds an indicator
“∞” lights.
5) Priority Channel Setting
A priority channel can be set as follows with the programming
software (KPG-49D).
1Specify a priority channel as a fixed priority channel.
2Make a selected channel a priority channel.
6) Scan Type According to the Priority Channel
1When no priority channel is set : Only the non-priority
channels are scanned.
If a non-priority channel stops temporarily, it stops until
there is no signal on the channel.
2When priority channel is set : Either priority channel is
scanned.
If a non-priority channel stops temporarily, a priority channel
signal is detected at certain intervals.
If a priority channel stops temporarily, it stops until there is
no signal on the priority channel.
7) Revert Channel
The revert channel is used to transmit during scanning and
set by the programming software (KPG-49D).
1Priority
The transceiver reverts to the priority channel
2Priority with talkback
The transceiver reverts to the priority channel.
If you press PTT during a resume timer (dropout delay time,
TX dwell time) or calling, you can transmit on current
channel to answer to the call however revert channel is set
to priority channel.
After resume time, scan re-starts and transmission channel
is return to priority channel.
3Selected channel
The transceiver reverts to the channel before scanning or
the channel that you changed during scan.
4Last called channel
The transceiver reverts to the last called channel during
the scan.
5Last used channel
The transceiver reverts to the last used (transmitted)
channel during scan. “Last used” revert channel includes
talkback function.
6Selected with talkback
The transceiver reverts to the channel before scanning or
the channel that you changed during scan.
8) Scan End
When you reactivate the key programmed to the scan
function during scan mode, the scan ends.
The scan icon “SCN” and “-SCAN-” or revert channel
(programmable) display goes off.
9) Temporarily Delete/Add
It is possible to delete or add channel temporarily during
scan. When scan stops on unnecessary channel for example
by interference of the other party, activate the delete/add
function (for example press the key), then that channel is
deleted temporarily and scan re-start immediately.
When you would like to add the deleted channel temporarily
to scan sequence, select the desired (deleted) channel during
scan, activate the delete/add function (for example press the
key) before scan re-start.
That channel is added temporarily to scan sequence. The
temporary deleted or added channels are returns to pre-set
delete/add, when the transceiver exits from scan mode.
4. Details of Features
4-1. In Case of Trunking Format/Conventional Format
1) Time-out timer
The time-out timer can be programmed in 15 seconds
increments from 15 seconds to ten minutes. If the transmitter
is keyed continuously for longer than the programmed time,
the transmitter is disabled and a warning tone sounds while
the PTT button is held down. The alert tone stops when the
PTT button is released.
2) Sub LCD
You can use 3-digit the display to display the system number,
channel number or group number. It is useful when the main
(12-digit) display indicates system, group or channel name or
other functions.
3) Selective Call Alert LED
You can select whether or not the LED on the transceiver
flashes in an orange color when selective call was occurred.
4) PTT ID
PTT ID provides a DTMF ANI to be sent with every time
PTT (connect ID at beginning of transmission, disconnect ID
at end of transmission, or both).
You can program PTT ID "on" or "off" for each group
channel. The contents of ID are programmed for each
transceiver.
The transceiver is capable to have ID. The format is DTMF.
The timing that the transceiver sends ID is programmable.
Connect ID : Connect ID is sent on beginning of transmission.
Disconnect ID : Disconnect ID is sent on end of transmission.
Both : Connect ID is sent on beginning of transmission and
disconnect ID is sent on end of transmission.
There is also "PTT ID" setting for each channel.
5) Radio password
When the password is set in the transceiver, user can not
use the transceiver unless enter the correct password.
This code can be up to 6 digits from 0 to 9 and input with
the keypad or selector, and “S” key.

TK-280
9
OPERATING FEATURES
6) Battery Warning
This transceiver has battery warning feature. If the low
voltage is detected during transmission, the transceiver warns
it by flashing red "LED".
Then more low voltage is detected during transmission, the
transceiver stops transmission and warns it by flashing red
"LED" and beep.
Please notice "standard" for the battery exchange, charging
time by flashing red LED and beep.
7) Minimum Volume
The minimum volume is programmable (off (0) to 31). The
transceiver remains the minimum volume level however the
mechanical volume position is set to zero.
4-2. In Case of Trunking Format
1) Call indicator
The call indicator can be programmed for each group. In
trunked system, it can be set to respond to a selectable decode
ID or one of two fixed IDs, except block IDs. When a call is
received with a selectable decode ID, the call indicator flashes.
When a call is received with a fixed ID, the call indicator lights
continuously.
On a conventional system, the call indicator can be
programmed to light for each QT or DQT code. It keeps flashing
while a call is being received. It is turned off by pressing any
front panel key.
2) Free system ringback
This feature is available only when a telephone
interconnected ID code is selected. If a busy tone sounds when
the PTT button is pressed, the transceiver enters this mode
automatically.
When the PTT button is released, a beep sounds for 400ms
to indicate that the mode has been entered. If the scan is on, it
is resumed (the “SCN” mark goes on). When any repeater
becomes available, a ringing tone sounds and this mode ends.
The mode is terminated when the system, group, scan, PTT,
key is changed.
3) System search
This feature can be programmed to automatically access
other programmed systems when the selected system cannot
be accessed. If an intercept tone sounds when the PTT button
is pressed after setting the mode, the transceiver has entered
the mode.
If the group ID is a telephone interconnect ID, the transceiver
then attempts to access, in succession, other systems that
have a telephone interconnect ID in the revert group location.
If the group ID is a dispatch ID, the transceiver attempts to
access other systems that have a dispatch ID programmed in
the revert group location.
If there is no system to be accessed, an intercept tone
sounds, the mode is terminated, and the transceiver returns to
the first system. If the access is successful, the mode is
terminated, and the searched system becomes the new
selected system (If during scanning, the scan stops).
4) Transpond
This feature can be programmed to turn on and off for each
group. If the ID of the group for which transpond is enabled is
received, two data messages (transmit ID and turn-off code)
are automatically transmitted if the PTT button is not pressed
as a response within the time set (0 to 300 seconds in 1-second
increments). If the PTT button is pressed within the time, the
transpond is not preformed.
5) Transmit inhibit
The transceiver can be programmed with a transmit inhibit
block of ID codes. If an ID code within this block is decoded
the preset time before the PTT button is pressed, transmission
is inhibited. The BUSY indicator lights and a busy tone sounds
until the PTT button is released to indicate that transmission is
not possible (except clear-to talk mode).
Transmission with the group for which the encode ID is not
set is inhibited, and the busy tone is output while the PTT button
is held down, regardless of the clear-to -talk setting.
6) Auto TEL
A telephone interconnect call can be made by simply
pressing the key by assigning this feature to the key. This
feature accesses the TEL channel of the available system
automatically.
When the key is pressed, a queue tone is output, and the
“AUTO TEL” appears on the alphanumeric display along with
a flashing handset indicator ( ) to indicate that this mode has
been entered. If the TEL ID is set for the revert system, the
TEL channel of that system is accessed. If all TEL channels
are busy, an attempt is made to access the TEL channels of
another system in which the TEL ID code has been pro-
grammed. It is repeated for 60 seconds until the access
succeeds. If the access succeeds, a dial tone returns from the
repeater. If the key is pressed again when the queue tone is
sounding, this mode is canceled.
If the access fails after 60 seconds, a deny tone is output
and this mode is terminated. When the talk ends, the revert
system/group returns. When the scan mode is effective, the
scan resumes. The Auto TEL feature can be programmed to
turn on or off for each system.
4-3. In Case of Conventional Format
1) "TOT" Pre-Alert
The transceiver has "TOT" pre-alert timer. This parameter
selects the time at which the transceiver generates "TOT" pre-
alert tone before "TOT" is expired.
"TOT" will be expired when the selected time passes from
a TOT pre-alert tone.
2) "TOT" Re-Key Time
The transceiver has "TOT" re-key timer. This timer is the
time you can not transmit after "TOT" exceeded. After "TOT"
re-key time expired you can transmit again.

TK-280
10
OPERATING FEATURES
3) "TOT" Reset Time
The transceiver has "TOT" reset timer. This timer is the
minimum wait time allowed during a transmission that will reset
the "TOT" count.
"TOT" reset time causes the "TOT" to continue even after
PTT is released unless the "TOT" reset timer has expired.
4) OST (Operator Selectable Tone)
The transceiver is capable to have "OST" function and 16
tone pair (QT/DQT) with max 10-digit name for each tone pair.
•"OST" Back Up
The transceiver is programmable the selected "OST" code
is memorized or not. If you set to Disable (no memorized), the
"OST" function always starts at "off".
•Direct "OST"
It is possible to call "OST" number directory using keypad.
In this case, keypad is used for "OST", then "Auto PTT" "Store
& Send" functions by keypad are not usable.
5) Clear to Transpond
The transceiver waits the transpond of 2-Tone/DTMF if
channel is busy until channel open. This feature prevents the
interference to other party.
6) Battery Save
This is the automatic battery saver during a standby mode
operation. The receiver circuit is repeated on and off to
conserve the battery life.
5. Option Signalling (DTMF/2 tone)
Built-in DTMF decoder is available for option signalling.
Built-in 2-Tone decoder is available for option signalling.
It is possible to use individual call, group call, DBD (Dead
Beat Disable). Note : DBD is only DTMF.
Preset operation is triggered when matches with Option
Signaling
When Option Signaling matches on a Group Channel where
set to Yes, the Option Signaling display flashes and Option
Signaling is canceled. Settings after this will cause “Transpond”
or “Alert” to sound.
Setting the Selective Call Alert LED will make an orange
LED start flashing.
Mute or Unmute is triggered by the ID/QT/DQT/Carrier when
option signaling is a match (when Option Signal is deactivated
by a transmission).
AND/OR
Option Signaling match conditions can be selected with
AND/OR logic.
Alert/Transpond AF Mute Open
AND
Triggers at match with QT/ Triggers at match with QT/
DQT/ID+DTMF(2tone);Both DQT/ID+DTMF(2tone); Both
OR LTR Format→Triggers at Triggers only for match with
match with QT/DQT/ID+DTMF QT/DQT/ID;Signaling
:Both
Conventional Format →
Triggers only for match with
DTMF (2tone) : Opt
Even if set for OR, AF mute cannot be canceled just by a
match with DTMF.
In conventional channels not set with QT/DQT, signaling is
a match just by receiving the carrier.
Auto Reset
When Option Signaling matches on a Group channel where
set to Yes, Option Signaling is canceled when it matches a
group channel set to Yes.
After Option Signaling is a match, Option Signaling can
automatically set to Reset after a specified time.
Dead Beat Disable
When the D.B.D (Dead Beat Disable) code is a match, a
preset operation is performed.
When D.B.D matches on all group channels regardless of
whether Option Signaling = Yes/No, then TX Inhibit or TX RX
Inhibit is activated by settings performed afterwards. D.B.D is
canceled when the D.B.D. code + “#” is received.
Transpond is always activated when the D.B.D code is a
match. Alert is not output. An Option Signaling match is not
displayed.
6. Audible user feedback tones
The transceiver outputs various combinations of tones to
notify the user of the transceiver operating state. The main
tones are listed below
The high tone is 1477Hz, the mid tone is 941Hz, and the
low tone is 770Hz.
•Power on tone
This tone is output when the transceiver is turned on. (The
high tone is output for 500ms.)
•Alert tone
This tone is output when the transceiver is TX inhibition for
TOT, battery warning and PLL unlocked. It is output until the
PTT button is released. (The 697Hz tone is output.)
•Busy Tone
In trunked mode (of trunking format) the busy tone informs
the user when the repeater cannot be used (System busy or
TX inhibit status).
In conventional mode (of conventional format), this informs
the user of a Busy Channel Lockout.

TK-280
11
OPERATING FEATURES/REALIGNMENT
• Group Call Tone
The group call tone informs the user of a group call in DTMF/
2Tone Option Signaling. This tone repeats 7 times.
•Individual Tone
Individual tone is issued on receiving selective call by DTMF/
2 Tone Option Signaling.
•Intercept tone (Trunking Format)
This tone indicates that the transceiver is out of range. It
indicates that the PTT button is pressed, and transmission has
started, but the repeater cannot be connected and talking is
not possible. It is output until the PTT button is released. (The
mid tone and low tone are output alternately in 200ms intervals.)
•Delay tone (Trunking Format)
This tone is output when the PTT button is pressed and the
repeater is accessed three times or more to indicate connection
with the repeater is delayed. This tone is the same as the busy
tone. (It is not output of CLEAT TO TALK has been set to
YES.)
•Proceed tone (Trunking Format)
This tone is output when the PTT button is pressed,
transmission starts, and the repeater is connected to indicate
that the user can talk if the Clear-to-talk function has been set.
(The high tone is output for 100ms.)
•Queue tone (Trunking Format)
This tone is output until the Auto TEL function is set and the
TEL channel is accepted successfully. (The mid tone on for
50ms, off for 50ms, and on for 50ms in 1 second intervals.)
•Deny tone (Trunking Format)
This tone is output if the Auto TEL function is set, the queue
tone is output, but the TEL channel cannot be accessed within
60 seconds. It is similar to the intercept tone. (The mid tone
and low tone are output alternately in 150ms intervals.)
•Free system ringback mode tone, system search mode
tone (Trunking Format)
This tone indicates that the transceiver is free system
ringback mode or system search mode. (The low tone is output
for 400ms.)
•Ringing tone (Trunking Format)
This tone indicates that the transceiver can use the repeater
in free system ringback mode. (The mid tone and no tone are
output eight cycles alternately in 50ms intervals.)
•Pre Alert tone (Conventional Format)
Informs user when nearing transmit inhibit (transmit cutoff)
time due to TOT.
The Pre Alert Tone is issued from the time set for TOT Pre
Alert until the TOT triggers.
1. Modes
REALIGNMENT
2000Hz 2000Hz 2000Hz
100ms 100ms 100ms 100ms 100ms
770Hz 770Hz
30ms 30ms 30ms
1633Hz 1633Hz 1633Hz
50ms 50ms 50ms 50ms 50ms
Mode Function
User mode For normal use.
Panel test mode Used by the dealer to check the
fundamental characteristics.
Panel tuning mode Used by the dealer to tune the radio.
PC mode Used for communication between the
radio and PC (IBM compatible).
Data program- Used to read and write frequency data
ming mode and other features to and from the radio.
PC test mode Used to check the radio using the PC.
This feature is included in the FPU.
See panel tuning.
Firmware program- Used when changing the main
ming mode program of the flash memory.
Clone mode Used to transfer programming data
from one radio to another.
Self programming Frequency, signalling and features
mode (Conventional write to the radio.
Format)
User mode
Panel test mode
PC mode
Firmware
programming mode
Clone mode
Self programming
mode (Conventional
Format)
Panel tuning mode
PC test mode
Data programming
mode
PC tuning mode

TK-280
12
5.PC Mode
5-1. Preface
The TK-280 transceiver is programmed by using a personal
computer, programming interface (KPG-36) and programming
software (KPG-49D).
The programming software can be used with an IBM PC or
compatible. Figure 1 shows the setup of an IBM PC for
programming.
5-2. Connection procedure
1. Connect the TK-280 to the personal computer with the
interface cable.
2. When the POWER switch on, user mode can be entered
immediately. When PC sends command the radio enter PC
mode, and “PROGRAM” is displayed on the LCD.
When data transmitting from transceiver, the red LED is
blinking.
When data receiving to transceiver, the green LED is blinking.
Notes:
•The data stored in the personal computer must match model
type, when it is written into the flash memory.
•Change the TK-280 to PC mode, then attach the interface
cable.
5-3. KPG-36 description
(PC programming interface cable: Option)
The KPG-36 is required to interface the TK-280 to the
computer. It has a circuit in its D-subconnector (25-pin) case
that converts the RS-232C logic level to the TTL level.
The KPG-36 connects the universal connector of the TK-
280 to the computers RS-232C serial port.
5-4. Programming software description
The KPG-49D programming disk is supplied in 3-1/2” disk
format. The software on this disk allows a user to program TK-
280 radios via programming interface cable (KPG-36).
5-5. Programming with IBM PC
If data is transferred to the transceiver from an IBM PC with
the KPG-49D, the destination data (basic radio information)
for each set can be modified. Normally, it is not necessary to
modify the destination data because their values are
determined automatically when the frequency range (frequency
type) is set.
The values should be modified only if necessary. Data can
be programmed into the flash memory in RS-232C format via
the universal connector.
KPG-49D instruction manual parts No. : B62-1096-XX
KPG-49D
Fig. 1
3. Panel Test Mode
Setting method refer to ADJUSTMENT.
4. Panel Tuning Mode
Setting method refer to ADJUSTMENT.
2. How to Enter Each Mode
Mode Operation
User mode Power ON
Panel test mode [A]+Power ON (Two seconds)
PC mode Received commands from PC
Panel tuning mode [Panel test mode]+[S]
Firmware programming mode [S]+Power ON (Two seconds)
Clone mode [C]+Power ON (Two seconds)
Self programming mode [LAMP]+Power ON
(Conventional Format) (Two seconds)
REALIGNMENT
6. Firmware Programming Mode
6-1. Preface
Flash memory is mounted on the TK-280. This allows the
TK-280 to be upgraded when new features are released in the
future. (For details on how to obtain the firmware, contact
Customer Service.)
6-2. Connection procedure
Connect the TK-280 to the personal computer (IBM PC or
compatible) with the interface cable (KPG-36). (Connection is
the same as in the PC Mode.)
6-3. Programming
1. Start up the programming software (KPG-49D), select
"firmware program" in the "Program" item, and press the
Return key on the personal computer. This starts up the
firmware programmer.
2. The top screen is displayed. Press any key to advance to
the next screen.
3. Set the communications speed (normally, 57600 bps) and
communications port in the Setup item.
4. Set the firmware to be updated by File select (=F1).
5. Turn the TK-280 power ON with the [S] switch held down.
Hold the switch down for two seconds until the display
changes to "PROG 57600". When "PROG 57600" appears,
release your finger from the switch.
6. Check the connection between the TK-280 and the personal
computer, and make sure that the TK-280 Is in the Program
mode.
7. Press F10 on the personal computer. A window opens on
the display to indicate progress of writing. When the TK-

TK-280
13
REALIGNMENT
Fig. 2
280 starts to receive data. the [P] icon is blinking.
8. If writing ends successfully. the LED on the TK-280 lights
and the checksum is displayed.
9. If you want to continue programming other TK-280 s, repeat
steps 5 to 8.
Notes:
●To start the Firmware Programmer from KPG-49D, the Fpro
path must be set up by KPG-49D Setup.
●This mode cannot be entered if the Firmware Programming
mode is set to Disable in the Programming software (KPG-
49D).
●When programming the firmware, it is recommend to copy
the data from the floppy disk to your hard disk before update
the radio firmware.
Directry copying from the floppy disk to the radio may not
work because the access speed is too slow.
6-4. Function
1. If you press the [MON] switch (top of left side) while "PROG
57600" is displayed, the checksum is displayed. If you press
the [MON] switch again while the checksum is displayed,
"PROG 57600" is redisplayed.
2. If you press the [LAMP] switch (bottom of left side) while
"PROG 57600" is displayed, the display changes to "PROG
19200" to indicate that the write speed is low speed (19200
bps). If you press the [LAMP] switch again while "PROG
19200" is displayed, the display changes to "PROG 38400",
and the write speed becomes the middle-speed mode
(38400 bps). If you press the [LAMP] switch again while
"PROG 38400" is displayed, the display returns to "PROG
57600".
Note:
Normally, write in the high-speed mode.
7. Clone Mode
Programming data can be transferred from one radio to
another by connecting them via their external universal
connectors. The operation is as follows (the transmit radio is
the master and the receive radio is a slave).
1. Turn the master TK-280 power ON with the [C] key held
down. If the password is set to the TK-280, the TK-280
displays "CLONE LOCK". If the password is not set, the
TK-280 displays "CLONE MODE".
2. When "CLONE LOCK" is displayed, only the knob (encoder)
and [S], and [0] to [9] keys can be accepted. When you
enter the correct password, and "CLONE MODE" is
displayed, the TK-280 can be used as the cloning master.
The following describes how to enter the password.
3. How to enter the password with the keypad;
If you press a key while "CLONE LOCK" is displayed. the
number that was pressed is displayed on the TK-280. Each
press of the key shifts the display in order to the left. When
you enter the password and press the [S] key, "CLONE
MODE" is displayed if the entered password is correct. If
the password is incorrect, "CLONE LOCK" is redisplayed.
How to enter the password with the encoder;
If the encoder is rotated while "CLONE LOCK" is displayed,
numbers (0 to 9) are displayed flashing. When you press
the [S] key, the currently selected number is determined. If
you press the [S] key after entering the password in this
procedure, "CLONE MODE" is displayed if the entered
password is correct. If the password is incorrect, "CLONE
LOCK" is redisplayed.
4. Power on the slave TK-280.
5. Connect the cloning cable (No. E30-3325-05) to the
universal connectors on the master and slave.
6. Press the [S] key on the master while the master displays
"CLONE MODE". The data of the master is sent to the slave.
While the slave is receiving the data, "PROGRAM" is
displayed. When cloning of data is completed, the master
displays "END", and the slave automatically operates in
the User mode. The slave can then be operated by the
same program as the master.
7. The other slave can be continuously cloned. When the [S]
key on the master is pressed while the master displays
"END", the master displays "CLONE MODE". Carry out the
operation in step 4 to 6.
Note:
Only the same models can be cloned together.
8. Self Programming Mode
Write mode for frequency data and signalling etc. Mainly
used by the person maintaining the user equipment.
8-1. Enter to the self programming mode
Delete R134 (SELF, Figure 3) in the TX-RX unit and turn
the power switch on while pressing the [LAMP] key. When
enter the self progrumming mode, “SELF PROG” is displayed.
Note :
This mode (self programming mode) cannot be set when it
has been disabled with the FPU.

TK-280
14
REALIGNMENT
8-2. Channel Setting Mode
This is a mode for making channel settings with the panel
keys without using the FPU.
Pressing [MON] when [SELF PROG] is displayed, sets
Channel Setting Mode.
Select an item set with [C] and change the selection with the
encoder.
The data displayed with [B] is stored in the memory and
then proceeds to the next item. Pressing [C] proceeds to the
next item without storing it in the memory.
Press [MON] to set the display to [SELF PROG] and return
to reset (default) status.
[MON]
Beat shift yes/no
[B]/[C]
[MON]
RF Power High/Low
[B]/[C]
[MON]
Busy channel lockout yes/no
[B]/[C]
[MON]
Scan delete/add
[B]/[C]
[MON]
TX signalling
[B]/[C]
[MON]
TX frequency
[B]/[C]
[MON]
RX signalling
[B]/[C]
[MON]
RX frequency
[B]
[MON]
Channel set mode
[MON]
Self programming mode
OFF
OFF QT
OFF
OFF
Channel selection Group selection
[MON]
Wide/Narrow
[B]/[C]
[LAMP]
[LAMP] [LAMP]
DQT N
[LAMP]
[LAMP]
DQT I
[S]
[LAMP]
[LAMP]
[C]
QT
[LAMP]
DQT N
[LAMP]
[LAMP]
DQT I
[S]
[B]/[C]
X57-5740
Foil Side
R134
●Flow Chart
Items set in Channel Setting Mode are as follows.
Function settings Display Remarks
Channel select CH or GRP
RX Frequency RXF [LAMP] : Freq. On/Off switching
[A] : 2.5kHz/5kHz/6.25kHz/
7.5kHz/1MHz step switching
RX Signalling RXS [LAMP] : OFF/QT/DQT switching
[A] : 1 step/Standard switching
[S] : DQT Normal/Invert swtiching
TX Frequency TXF Key operation same as RX
Frequencies
TX Signalling TXS Key operation same as RX
Signalling
Scan Del/Add SCN Delete/Add
Busy Channel BSY YES/NO
Lockout
RF Power PWR HIGH/LOW
Beat Shift SFT YES/NO
Wide/Narrow W/N Wide/Narrow
Fig. 3

TK-280
15
REALIGNMENT
8-3. Function Setting Mode
This is a mode for using the panel keys to make function
settings without using the FPU, that operate on all channels.
Pressing the [LAMP] when [SELF PROG] is displayed, sets
the Function Setting Mode.
Select an item set with [C] and change the selection with
the encoder.
Press [LAMP] to display [SELF PROG] and return to reset
(default) status.
Items set in Function Set Mode are as follows.
Function settings Display Remarks
[A] A Key Function
[B] B Key Function
[C] C Key Function
[LAMP] LAMP Key Function
[S] S Key Function
[MON] MON Key Function
[AUX] AUX Key Function
[KNOB] KNB Knob Function
T.O.T TOT ON/OFF at T.O.T all settings
ON:TOT[60s]/Pre-Alert[10s]/
Rekey Time[5s]/Reset Time[5s]
OFF:TOT[600s]/Pre-Alert[Off]/
Rekey Time[Off]/Reset Time[Off]
Beep BEP ON/OFF at BEEP all settings
ON:Power On Tone[On]/
Control Tone[On]/Warning Tone[On]
OFF:Power ON Tone[Off]/
Control Tone[Off]/
Watning Tone[Off]
Battery Save BAT OFF/SHORT/MEDIUM/LOG
●Flow Chart
[LAMP]
Knob select function
[B]/[C]
[LAMP]
[AUX] key function
[B]/[C]
[LAMP]
[MON] key function
[B]/[C]
[LAMP]
[S] key function
[B]/[C]
[LAMP]
[LAMP] key function
[B]/[C]
[LAMP]
[C] key function
[B]/[C]
[LAMP]
[B] key function
[B]/[C]
[LAMP]
[A] key function
Functionset mode
[LAMP]
Self programming mode
[LAMP]
Battery Save short/medium/long
[B]/[C]
[LAMP]
Beep on/off
[B]/[C]
[LAMP]
T.O.T on/off
[B]/[C]
[B]/[C]
8-4. Memory Reset Mode
This mode is used to clear data for functions that can be set
in Self Programming Mode or to return to reset values (default).
Pressing [S] when [SELF PROG] is shown, sets the display
to [CLEAR NO?].
Turning the encoder alternately switches the display
between [CLEAR NO?] [CLEAR YES?].
Pressing [S] when [CLEAR YES?] is shown, clears the data
and sets the display to [ALL CLEAR].
Pressing [S] again, returns the display to [SELF PROG].
Pressing [S] when [CLEAR NO?] is shown, returns the
display to [SELF PROG] without resetting the data.

TK-280
16
Fig. 2 Receiver section
IC12
MIX, DET, IF SW
Q15
DMDM
IC4 (2/2)
AF AMP
5
DE-
EMP MUTE
EXP
HPF LPF HPF BEF
IC13 21
VOL
IC8
IC7 (2/2)
AF AMP
41
VC1
VC2
Q310
SSW
INT.
SP
EXT.
SP
2nd local
OSC
X2
AF AF
SW
IC300
AF PA
ANT
SW
L39,41
L43,44,
46,47,
48
BPF
D12
D14,22
Q24
RF
AMP
ANT
IC18
1st MIX
Q12
1st IF
L27,29
BEF
L31,33
BPF XF1
MCF
1st Local
OSC (PLL)
CF1 : Wide
CF2 : Narrow
1. Overview
This transceiver is VHF/FM portable transceiver designed
to operate in the frequency range of 146 to 174MHz (K, K3, M)
and 136 to 162MHz (K2, K4).
2. Circuit Configuration by Frequency
The receiver is a double-conversion superheterodyne with
a first intermediate frequency (IF) of 44.85MHz and a second
IF of 455kHz. Incoming signals from the antenna are mixed
with the local signal from the PLL to produce the first IF of
44.85MHz.
This is then mixed with the 44.395MHz second local
oscillator output to produce the 455kHz second IF. This is
detected to give the demodulated signal.
The transmit signal frequency is generated by the PLL VCO,
and modulated by the signal from the microphone. It is then
amplified and sent to the antenna.
ANT
TX/RX : 146~174MHz (K,K3,M)
136~162MHz (K2,K4)
ANT
SW
RF
AMP
PA
AMP
TX
AMP
1st MIX MCF
44.85MHz
CF
455kHz
FM IF
SYSTEM
AF
AMP SP
44.395MHz
186.85~206.85MHz (K2,K4)
190.85~218.85MHz (K,K3,M)
PLL
VCO MIC
AMP MIC
146~174MHz (K,K3,M)
136~162MHz (K2,K4)
Fig. 1 Frequency configuration
3. Receiver System
3-1. RF unit
An incoming RF signal from the antenna terminal is passed
through the antenna switch (D12, D14. and D22 are off) and
then the bandpass filter (L43,44,46,47,48). The bandpass filter
is adjusted by a variable capacitor. The input voltage to the
variable capacitor is regulated by the voltage output from the
D/A converter (IC8). The signal is amplified by RF amplifier
(Q24), and passed through the bandpass filter (L31,33) and
band-eliminate filter (L27,29) to remove the spurious signal
again. The resulting signal is applied to the first mixer (IC18),
where it is mixed with the first local oscillator signal output
from the frequency synthesizer to produce the first IF
(44.85MHz). The 1st mixer uses the GaAs IC.
3-2. IF unit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF1) to remove a adjacent channel signal. The
filtered first IF signal is amplified by the first IF amplifier (Q12)
and then applied to the lF system IC (IC12). The IF system IC
provides a second mixer, second local oscillator, limiting
amplifier, quadrature detector and RSSI (Received Signal
Strength Indicator). The second mixer mixes the first IF signal
with the 44.395MHz of second local oscillator output (crystal
unit X2) and produces the second IF signal of 455kHz.
The second IF signal is passed through the ceramic filter
(CF1; Wide, CF2 ; Narrow) to more remove the adjacent
channel signal. The filtered second IF signal is amplified by
the limiting amplifier and demodulated by the quadrature
detector with ceramic discriminator (CD1). The demodulated
signal is routed to the audio circuit.
3-3. Wide/Narrow changeover circuit
Narrow and Wide settings can be made for each channel
by switching the ceramic filters CF1 (Wide), CF2 (Narrow).
The WIDE (high level) and NARROW (low level) data is
output from IC19 (microcomputer) pin 99.
When a WIDE (high level) data is received, Q6 turn off and
Q7 turn on. When a NARROW (low level) data is received,
Q6 turn on and Q7 turn off. D5, D7 are switched to ceramic
filters when a high/low level data is received.
Q9 turns on/off with the Wide/Narrow data and the IC12
detector output level is changed to maintain a constant output
level during wide or narrow signals.
CIRCUIT DESCRIPTION

TK-280
17
CIRCUIT DESCRIPTION
5R
Q6
Q7 D5
R39
R42
C50
C268
R47
D7
R56
W/N "H" : Wide
"L" : Narrow
MXO IFI
MXI
AFO
DM
C93
R99
R71
C76
IC12
FM IF SYSTEM
Q12
C60 R46
C48
CF1
CF2
R43
Q15 C266
Q9
C91
R74
W/N
Fig. 3 Wide/Narrow changeover circuit
3-4. Audio amplifier circuit
The demodulated signal from IC12 goes through the mute
switch (Q15) and is amplified by IC4 (2/2), high-pass filtered,
low-pass filtered, high-pass filtered, band-eliminate filtered, and
de-emphasized by IC13.
The signal then goes through an AF amplifier IC7 (2/2), an
electronic volume control (IC8), and an AF switch (Q310 is
on), and is routed to audio power amplifier (IC300), where it is
amplified and output to the internal speaker.
The audio mute signal (AM) from the shift register becomes
Low in the standby and Q304, Q305 which are power supply
circuit for IC300 turn off. Also, IC13 is set to the power down
mode according to data from microprocessor, and the AF signal
is muted. When the audio is output, AM becomes High to turn
Q304, Q305 ON, and voltage is supplied to power terminal VP
of IC300. Also, IC13 is canceled out of the power down mode.
The speaker is switched by the logic of speaker switching
terminal SSW on the universal connector. When SP-MIC is
not attached, the logic of SSW becomes High and SW (Q310)
is turned ON, and the AF signal is input to both amplifiers of
IC300.
When SP-MIC is attached, SSW is connected to GND at
inside of SP-MIC. For this reason, Q310 is turned OFF, and
the AF signal is input only to amplifier for EXT SP of IC300.
Change of INT/EXT SP refer to Fig. 4.
AM SSW VC1 VC2 SP
HH HLINT
HL LHEXT
LH LLMUTE
LL LLMUTE
Fig. 4 Audio amplifier circuit
SW
IC300
2
8
AM
AF
SSW
INT.SP
EXT.SP
Q305
Q304
SB
VP 5
VC1
VC2
Q308
Q301
Fig. 6 Squelch and RSSI voltage vs ANT input level
Fig. 5 Squelch circuit
12
DET
BPF
AMP
DET
RSSI NOISE
AMP
IC19
CPU
IF AMP
7
91
93
IC12 : FM IF IC
Q4 D4
SQ close
SQ open
Preset
value
ANT input level
SQ voltage
ANT input level
RSSI voltage
Preset balue
3-5. Squelch circuit
The output from IC12 enters FM IC again, then passed
through a band-pass filter. The noise component output from
IC12 is amplified by Q4 and rectified by D4 to produce a DC
voltage corresponding to the noise level. The DC voltage is
sent to the analog port of the CPU (IC19). And IC12 outputs a
DC voltage (RSSI) corresponding to the input of the IF amplifier.
The CPU reads the RSSI signal via pin 93.
IC19 determines whether to output sounds from the speaker
by comparing the input voltage of pin 91 and pin 93 with the
preset value.
4. Transmitter System
4-1. Microphone amplifier
The signal from the internal microphone goes through the
mute switch (Q300).
When the SP-MIC is not attached, the microphone switching
terminal (MSW) on the universal connector becomes High, and
mute switch (Q300) is turned ON. When the SP-MIC is

TK-280
18
4-3. APC circuit
The APC circuit always monitors the current flowing through
the RF power amplifier (IC100) and keeps a constant current.
The voltage drop at R244, R246 and R248 is caused by the
current flowing through the RF power amplifier and this voltage
is applied to the differential amplifier (IC23 1/2).
IC23(2/2) compares the output voltage of IC23(1/2) with
the reference voltage from IC8, and the output of IC23(2/2)
controls the VGG of the RF power amplifier to make the both
voltages to same voltage.
The change of power high/low is carried out by the change
of the reference voltage. Q22,23 and 25 are turned on in
transmit and the APC circuit is active.
5. Frequency Synthesizer Unit
5-1. Frequency synthesizer
The frequency synthesizer consists of the VCXO (X1), VCO
(A1), PLL IC(IC14) and buffer amplifiers.
The VCXO generates 16.8MHz. The frequency stability is
1.5ppm within the temperature range of -30 to +60˚C. The
frequency tuning and modulation of the VCXO are done to
apply a voltage to pin 1 of the VCXO. The output of the VCXO
is applied to pin 8 of the PLL IC.
The TK-280’s VCO consists of 2VCO and covers a dual
range of the 190.85~218.85MHz (K,K3,M), 186.85~206.85MHz
(K2,K4) and the 146~174MHz (K,K3,M), 136~162MHz (K2,K4).
The VCO generates 190.85~218.85MHz (K,K3,M),
186.85~206.85MHz (K2,K4) for providing to the first local signal
in receive. In TX, the pin 3 of the VCO goes low and the VCO
generates 146~174MHz (K,K3,M), 136~162MHz (K2,K4).
The output of the VCO is amplified by the buffer amplifier
(Q16) and routed to the pin 5 of the PLL IC. Also the output of
the VCO is amplified by the buffer amplifier (Q18) and routed
to the next stage according to T/R switch (D9, D23).
The PLL IC consists of a prescaler, fractional divider,
reference divider, phase comparator, charge pump. This PLL
IC is fractional-N type synthesizer and performs in the 40, 50
or 60kHz reference signal which is eighth of the channel step
(5, 6.25 or 7.5kHz). The input signal from the pins 5 and 8 of
the PLL IC is divided down to the 40, 50 or 60kHz and compared
at phase comparator. The pulsed output signal of the phase
comparator is applied to the charge pump and transformed
into DC signal in the loop filter (LPF). The DC signal is applied
to the pin 1 of the VCO and locked to keep the VCO frequency
constant.
PLL data is output from DT (pin 75). CP (pin 19) and EP
(pin 47) of the microprocessor (IC19). The data are input to
the PLL IC when the channel is changed or when transmission
is changed to reception and vice versa. A PLL lock condition
is always monitored by the pin 31 (UL) of the microprocessor.
When the PLL is unlocked, the UL goes low.
CIRCUIT DESCRIPTION
Fig. 7 Microphone amplifier
12 HPF LPF HPF IDC
PRE
EMP
ALC COMP
SW
LIMIT
SW
MIC
Q300 D8
MIC
EXT.
MIC
Q301
IC13 15 16 18 19
Q13
MUTE DTMF
98
6
D/A
D/A
IC8
IC8 IC1
I5 O5
I1 O1
D/A
IC8
I2 O2
LSD DI9
IC7 (1/2)
SUM
AMP
BUFF
AMP VCXO
VCO
A1
X1
MIC
MUTE
Q17
PTTMSW
attached, MSW is connected to GND at inside of SP-MIC. For
this reason, Q300 is turned OFF, the internal microphone is
muted, and only the input of the external microphone is supplied
to the microphone amplifier of the TX-RX unit.
The signal from microphone passes through the limitter
circuit in D8, and Mic mute switch (Q17 is off in TX) and through
the high-pass filter, the ALC circuit, the low-pass filter, the high-
pass filter, and pre-emphasis/IDC circuit in IC13. When
encoding DTMF, mute switch (Q13) is turned OFF for muting
the microphone input signal.
The signal passes through the D/A converter (IC8) for the
maximum deviation adjustment, and enters the summing
amplifier consisting of IC7 (1/2), and is mixed with the low speed
data from the CPU (IC19) and 9600bps DATA from Optional
Board Terminal.
The output signal from the summing amplifier passes
through the D/A converter (IC8) again and goes to the VCO
modulation input.
The other output signal from the summing amplifier passes
through the D/A converter (IC8) again for the BAL adjustment,
and the buffer amplifier (IC1 : 2/2), and goes to the VCXO
modulation input.
Fig. 8 Drive and final amplifier and APC circuit
From
T/R SW
(D9)
DRIVE
AMP
RF
POWER AMP LPF
ANT
SW
D12
ANT
VGG
Q20 IC100
VDD
R244
R246
R248
+B
IC23
(1/2)
IC23
(2/2)
REF
VOL
(IC8)
4-2. Drive and Final amplifier
The signal from the T/R switch (D9 is on) is amplified by
drive amplifier (Q20) to 30mW.
The output of the drive amplifier is amplified by the RF power
amplifier (IC100) to 5.0W (1W when the power is low). The RF
power amplifier consists of two stages MOS FET transistor.
The output of the RF power amplifier is then passed through
the harmonic filter (LPF) and antenna switch (D12 is on) and
applied to the antenna terminal.

TK-280
19
CIRCUIT DESCRIPTION
Fig. 9 PLL block diagram
Fig. 10 Memory circuit
T/R
(TX : Low)
T/R A1
VCO
CV
5
IC14
PLL
8
BUFF
BUFF
LPF
DT,CP,EP
CPU
UL
IC19
VCXO IC1
FC
BAL
Q18
SW
D9 To
drive
amp
Q16
X1
To mixer
SW
MB
D23
18
IC19
IC17
CPU
IC20
EEPROM
FLASH
6-2. Low battery warning
The battery voltage is monitored by the microprocessor
(IC19). When the battery voltage falls below the voltage set by
the Low Battery Warning adjustment, the red LED flashes to
notify the operator that it is time to replace the battery. If the
battery voltage falls even more (approx. 5.8V), a beep sounds
and transmission is stopped.
6. Control Circuit
The control circuit consists of microprocessor (IC19) and
its peripheral circuits. It controls the TX-RX unit and transfers
data to and from the display unit. IC19 mainly performs the
following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading system, group, frequency, and program data
from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off by the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit by decode data input.
6) Transmitting tone and encode data.
6-1. Memory circuit
Memory circuit consists of the CPU (IC19) and a flash
memory (IC17), a flash memory has a capacity of 2M bits that
contains the transceiver control program for the CPU and data
such as transceiver channels and operating features.
This program can be easily written from an external devices.
Data. such as operating status, are programmed into the
EEPROM (IC20).
●Flash Memory
Note : The flash memory holds data such as written with the
FPU (KPG-49D), firmware program (User mode, Test mode,
Tuning mode, etc.) This data must be rewritten when replacing
the flash memory.
●EEPROM
Note : The EEPROM stores tuning data (Deviation, Squelch,
etc.).
Realign the transceiver after replacing the EEPROM.
Low battery warning
The red LED flashes during
transmission
The red LED flashes and
continuous beep sounds
while PTT pressed
Battery condition
The battery voltage is low but
the transceiver is still usable.
The battery voltage is low and
the transceiver is not usable
to make calls.
6-3. Key input
If the clock is supplied to CLK terminal when the RES
terminal (CPU pin 78) of the decade counter (IC301) is set to
Low, Q0 to Q7 become High sequentially. Normally, KI1 and
KI2 are Low (pulled down). When any key is pressed. KI1 or
KI2 become High. The CPU detects which key is pressed,
according to the voltage of KI1 and Kl2 and clock timing.
Fig. 11 Key input
IC19
CPU
Q5
Q1
Q0
Q2
Q6
Q7
Q3
Vss
Vdd
RES
CLK
CL
CA
Q9
Q4
Q8
KI1
KI2
CK
KRST
IC301
16 keys
RESET
CLOCK
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
CLOCK
INHIBIT
CARRY
OUT
Fig. 12 Decade counter timing chart

TK-280
20
Fig. 14 Decode
IC13
AF IC
IC2
BPF
IC4
AMP
IC11
LPF
IC16
DTMF
DECODE
DCK,SD,STD
LSD
IN
HSD
IN
IC19
CPU
IC22
IC13
XOUT OSC1
PD
11
3
95
DT,CK,CE
CIRCUIT DESCRIPTION
Fig. 13 Encode
SUM
SUM
IC7(1/2)
SUM
R166 R162
C176 C170
R136
1
LSD
OUT
HSD
OUT
IC19
CPU
O5
O2
O3
O6
I2
I1
I5
IC8
D/A (ADJ)
VCO
MD A1
RX Audio
MIC IN
IC13
2LPF
IC10
I6
I3
VCXO
X1
MB
AF
AMP
IC7 (2/2)
O1 BUFF
AMP
IC1
7-2. Decode
●Low-speed data (QT,DQT,LTR)
The demodulated signal from the IF IC (IC12) is amplified
by IC4 (2/2) and passes through a low-pass filter (IC11) to
remove audio components. The signal is input to pin 95 of the
CPU.
The CPU digitizes this signal, performs processing such as
DC restoration, and decodes the signal.
●High-speed data (DTMF)
The DTMF input signal from the IF IC (IC12) is amplified by
IC4 (2/2) and goes to IC16, the DTMF decoder. The decoded
information is then processed by the CPU. During transmission
and standby, the DTMF IC is set to the power down mode
when the PD terminal is High. When the line is busy, the PD
terminal becomes Low, the power down mode is canceled and
decoding is carried out.
●High-speed data (2 tone)
The demodulated signal from the IF IC (IC12) is amplified
by IC4 (2/2) and passes through an audio processor (IC13)
and band-pass filter (IC2) to remove a low-speed data. The
CPU digitizes this signal, performs processing such as DC
restoration, and decodes the signal.
●MSK (ESN)
The MSK input signal from the IF IC is amplified by IC4 (1/
2) and goes to pin 5 of IC13. The signal is demodulated by
MSK demodulator in IC13. The demodulated data goes to the
CPU for processing.
7. Signalling Circuit
7-1. Encode
●Low-speed data (QT,DQT,LTR)
Low-speed data is output from pin 1 of the CPU. The signal
passes through a low-pass CR filter, and goes to the summing
amplifier (IC7 1/2). The signal is mixed with the audio signal
and goes to the VCO (A1) and VCXO (X1) modulation input
after passing through the D/A converter (IC8) for BAL
adjustment.
●High-speed data (DTMF)
High-speed data is output from pin 2 of the CPU. The signal
passes through a low-pass filter consisting of IC10, and
provides a TX DTMF tone and a RX DTMF tone. TX DTMF
deviation making an adjustment by microprocessor is passed
through the D/A convertor (IC8) and then applied to the audio
processor (IC13).
The signal is mixed with the audio signal and goes to the
VCO and VCXO. The RX DTMF tone is passed a summing
amplifier (IC7 2/2). The D/A converter (IC8) for audio control,
audio power amplifier and then to the speaker.
●MSK (ESN)
ESN utilizes 1200bps MSK signal. MSK signal is output from
pin 6 of IC13. The signal passes through the D/A converter
(IC8) for the MSK deviation adjustment. and is routed to the
VCO. When encoding MSK, the microphone input signal is
muted.