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DESCRIPTION

The D-21A(/K), D-24A(/K), and D-26A(/K) are
digitally coded stationary radio transmitters
triggered by normally open (N/O) or normally
closed (N/C) sensors. These transmitters can
be programmed to activate any of Linear’s
standard digital receivers that are tuned to the
same frequency. Each transmitter can perform
many remote switching tasks and are typically
used in wireless/hardwire security systems.
Each unit is powered by a self-contained 9-volt
battery and can be connected to various
sensors with the built-in screw terminals.

 

NOTE: Transmitters with a /K model number
suffix are Linear’s Canadian models tuned to 318
MHz. These instructions pertain to both the /K
and standard 303.875 MHz U.S. models.

D-21A N/O TRANSMITTER

The D-21A is used with various types of security
sensors that are 

normally open

 (magnetic

contacts, security floor mats, etc.). 

The D-21A

transmits a signal when the sensor circuit

closes.

 

The transmitter triggers instantly, and

may be re-triggered after a 30-second reset time.
A pushbutton is provided for battery/transmission
test. Pressing the pushbutton 

with the sensor

circuit open

 (after the 30-second reset) triggers

the transmitter and turns on the red LED if the
battery is above 7.5 volts.

D-24A N/C TRANSMITTER

The D-24A is used with various types of security
sensors that are 

normally closed

 (magnetic

contacts, security window screens, etc.). 

The

D-24A transmits a signal when the sensor
circuit 

opens.

 The transmitter incorporates a

time delay of 1 to 3 seconds, ensuring that the
sensor circuit must be continuously open for at
least 1 second before the D-24A will transmit.
This feature helps prevent activation from
short-term, spurious signals, and from signals
made from outside electromagnetic sources.
The transmitter may be re-triggered after a
30-second reset time. The transmitter has a
pushbutton for battery/transmission test.

 

NOTE: On the D-24A, the loop input terminals
must be closed for a minimum of 45 seconds
before the pushbutton will activate the
transmitter.

D-26A N/O TIME-DELAY TRANSMITTER

The D-26A is used with various types of security
sensors that are 

normally open.

 The

special-purpose D-26A transmitter has a built-in
exit/entry time delay. 

The timer starts when the

sensor circuit 

closes.

 

It begins a 5 to 10 second

countdown. If no action is taken before the time
delay is completed, the transmitter will send an
alarm signal to its companion receiver. 

Pressing

the pushbutton before the time delay period
has elapsed will prevent signal transmission.

In addition to canceling time-delayed signal
transmission, the pushbutton is used to test the
battery. Pressing the button turns on the red
LED if the battery is in good condition. 

The LED

does not light upon transmission.

 

NOTE: The each transmitter contains a timing
circuit that allows a single transmission of a
2-second duration to occur, followed by a
30-second reset time. This means that regardless
of the number of times the transmitter is triggered,
it will not send a signal more often than once every
30 seconds.

CODE SWITCH LOCATION

The digital coding switch is attached to the circuit
board inside the case. To access the switch,
unsnap and slide off the back cover as shown in
Figure 1, exposing the battery, lead wire screw
terminals, and digital coding switch (see Figure 2).

CODE SETTING

 

CAUTION! All transmitters and receivers must be
re-coded by installer prior to operation. DO NOT
USE THE FACTORY SET CODE!

Among the 256 possible codes, four codes are
considered invalid, and should not be used. They
are: all keys ON, all keys OFF, and keys set
alternating ON/OFF or OFF/ON combinations.
To set a code, select any valid combination of
ON and OFF positions for the switch keys
numbered 1 through 8.

Use a pointed object (other than a pencil or pen)
to set the keys. The ON position is when the top
of the switch is down, facing the numbers. The
OFF position is when the top of the switch is up
and the bottom is down, away from the numbers.
In the example shown in Figure 3, keys 1,4,6
and 8 are ON; keys 2,3,5 and 7 are OFF.

INSTALLATION

To mount the transmitter, proceed as follows:

STEP 1:

 Select a location for the transmitter and

drive screws through the two countersunk holes of
the back cover to mount the cover (see Figure 4).

 

NOTE: Generally, the higher the transmitter is
mounted above ground level (minimum of 3
feet) the better the radio range should be.

STEP 2:

 For recessed switches with hidden

wiring, fish the sensor wires through the wire
access hole on the back cover. With surface
wiring, route the wire leads through the wire slot
on the back cover (see Figure 4).

Codesetting Instructions for D-21, 24, 26 (/K)
Linear P/N: 200105 C
Size: 11.50" W x 5.75" H
Ink: PMS 285 (Blue) & Black
Material: 70 Lb. White Coated

Codesetting Instructions for D-21, 24, 26 (/K)
Linear P/N: 200105 C
Size: 11.50" W x 5.75" H
Ink: PMS 285 (Blue) & Black
Material: 70 Lb. White Coated

Figure 1.

Removing

the

Transmitter

Back Cover

9-VOLT
BATTERY

SCREW
TERMINALS

CODING
SWITCH

Figure 2.

Transmitter

Components

O

F

F

O

N

6

5

4

3

2

1

7

8

Figure 3. Example

Coding Switch

MOUNTING
SCREWS

SURFACE
WIRING
SLOT

RECESSED
WIRING
HOLE

Figure 4. Transmitter

Back Cover Mounting

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