Bell 208 A/B modem
Bell 208 A, Bell 208 B -
208 A: Synchronous data transmission, full-duplex operation over 4-wire leased lines, half-duplex operation over 2-wire leased lines; 4800-bps data rate. 208 B: same as 208 A, but over 2-wire dialup lines. Comparable to ITU V.27. The first standards to enable higher-speed data transmission (4800 bps) over leased lines for multipoint, multidrop networks. For example, these standards enable us connect IBM mainframes at a central office to terminals in branch office, with fewer modems.
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Reliable 4,800bps transmission over bad lines with 208A/B and 208 AB/AS (DPSK 8 phase) modem. Multi-Point / Multi-Drop, Dial, 2 or 4 wire lease line.
UDS 208 SERIES 4800 bps
Eight-phase differentially coherent phase shift keying.
4800 Hz ? 0.0 1 % Frequency
Transmit Clock 4800
Hz ? 0.02 % Frequency
0, -2, -4, -6, -8. -9, -10, -12 dBm and externally programmed.
600 ohms, transformer coupled and transient
2-wire, half-duplex PSTN or private line operation
and 4-wire full-duplex operation.
Conforms to EIA Standards RS-232-C and CCITT V.24.
FCC registered direct connect or leased line circuit.
to Send Delay
8.5 ms, 50 ms, or 150 ms
0 to -34 dBm for private lines or 0 to -44 dBm for PSTN network.
Equalized for C2 conditioned lines or for 3002 unconditioned lines.
Rotary switch for Analog and Digital Loopback,
Self Test, Transmit Test Pattern, Receive Test
Pattern, Data and Talk modes.
THE MODEM POWER SUPPLY
The standalone 208A/B modem unit contains a linear type power supply. All the power supply components are contained on the modem board except for the ac step down transformer.
The maximum ac power input to the unit at a line voltage of 110 Vac is 10 watts. The maximum dc power used by the unit is 3.5 watts.
THE MODEM TRANSMITTER
The UDS 208 A/B transmitter is a 4800 bits per second synchronous quadrature modulated transmitter with a Bell 208A/B compatible data scrambler. The transmitter provides the option of a strap selectable fixed pre-equalizer to improve performance on poor quality phone lines.
THE MODEM RECEIVER
The UDS 208A/B receiver is a 4800 bit per second synchronous quadrature demodulator with a Bell compatible 208A/B descrambler. The receiver front-end contains an improved adaptive equalizer that provides for dynamic telephone line equalization.