Hal Communications DKB-2010, Instruction Manual, Page: 12 / 101

10
2.4 RTTY Loop Connections
Since the RTTY output stage of the keyboard is isolated from ground and from the chassis, the keyboard
can be connected at any convenient point in the station loop circuit, provided that the voltage from either
loop connection to ground does not exceed 250 volts. Loop current is switched by a transistor, rated to carry
up to 80 mA DC and to withstand loop voltages up to 250 volts DC. Before making any connections to the
keyboard, measure the loop voltage in the space condition and the current during mark pulses to make
certain that neither exceeds the keyboard ratings.
UNPLUG THE KEYBOARD AND THE STATION LOOP SUPPLY BEFORE TAKING ANY
CONNECTIONS.
A typical station loop circuit is shown in Figure 2.3. A 6 pin plug is used to connect the loop to the
keyboard. Break the loop circuit at the desired point and connect the positive lead to pin 1 of the plug.
Connect the negative lead to pin 3. The cable shield, if one is used, may be connected to pin 2. A jumper
(or additional RTTY equipment) should be connected between pins 4 and 6. Double check the polarity of the
loop leads, as reverse voltages may damage the switching transistor. Then insert the plug into the RTTY
LOOP jack on the keyboard rear panel.
If the negative loop keying lead is grounded, the connections shown in Figure 2.4 should be used.
Prepare the plug connections as shown in Figure 2.4A.