Table 2-1. Channel Frequencies

TM 11-5895-1123-34

b. The TTY Processing System can process a

TTY entrance panel pass thru the Central Distribu-

maximum of nine full duplex TTY channels to include:

tion Frame (CDF) and terminate on the TTY

(1) Five external Frequency Shift Keyed (FSK)

Patch-VF panel at the input to the nine channel filter

channels.

bridge.

(2) One low level TTY channel.

d. nine channel TTY filter bridge is provided

(3) Three high level TTY channels which can

with 16 pairs of channel cards (16 for transmit and 16

be used for low level TTY if three high level TTY chan-

for receive) which will allow the nine channels to

nels are not required.

operate at any nine of the 16 frequencies listed in

c. The five FSK TTY channels from the voice (VF)

table 2-1.

Table 2-1. Channel Frequencies

Channel frequencies

Center frequency

Space frequency

Mark frequency

(Hz)

425

467.5

382.5

595

637.5

552.5

765

807.5

722.5

935

977.5

892.5

1105

1147.5

1062.6

1275

1317.5

1232.5

1445

1487.5

1402.5

1615

1657.5

1572.5

1785

1827.5

1742.5

1955

1997.5

1912.5

2125

2167.5

2082.5

2295

2337.5

2252.5

2465

2507.5

2422.5

2635

2677.5

2592.5

2805

2847.5

2762.5

2975

3017.5

2932.5

k. An additional low level TTY user channel is

The receive and transmit frequencies are normally

the same for any particular channel.

available which comes from the VF/TTY entrance panel

e. Each TTY input is patched from the TTY Patch-

through the CDF directly to the TTY Patch panel.

l. The internal CSS teletype which is low level TTY

VF panel to the channel on the nine channel TTY bridge

which is set to operate at its appropriate frequency.

can also be patched into one of the FSK keyers via the

f. The output from the nine channel TTY bridge is

TTY Patch panel in lieu of a field user.

m. The outputs of the four FSK keyers ultimately

a composite VF signal of the inputs which is fed to the

input of the multiplexer as one VF channel via the VF

are combined with the five external FSK users in the nine

patch panel.

channel TTY filter bridge to form the composite VF signal

g. A maximum of three high level TTY inputs can

allotted as the one input VF channel for the multiplexer.

n. During the receive operation, a composite VF

be sent to the inputs of three separate CU-1819/T

isolators which convert the high level TTY voltage of

signal is received from one VF channel of the multiplexer

neutral to 130 volts (20 ma or 60 ma) or +60 volts (2 ma)

and is fed back through the receive channels of the nine

polar to low level TTY voltages of +6 volts before they

channel TTY filter bridge where it is separated, by

are patched to the low level TTY patch panel.

filtering, into nine separate TTY channels.

h. From the TTY Patch panel, the high level TTY

o. The separated channels are patched back

channels can be patched to any three of the four FSK

through the TTY Patch-VF.

p. Five of the channels are then sent to the five

keyers which convert them into audio/tones to interface

with three of the input channels of the nine channel TTY

FSK field users, with the remaining four channels being

filter bridge.

patched through the four FSK converters which converts

i. The FSK keyers can be set to operate at any of

them from FSK VF signals back to low level TTY.

q. The outputs of three converters at the TTY

the 16 channel frequencies listed for the nine channel

TTY filter bridge.

j. The three FSK keyers can be used to process

low level TTY user data, instead of high level by

bypassing the CU-1819/T isolators via patching and

applying them directly to the TTY Patch panel.

2-5