Barnett Engineering B1474 User Manual
RA DIO MO DEM
B1474
OP ER A TION MAN UAL
April, 1998
Manual Revision 4.1
(for Version 2.1 Hardware)
TA BLE OF CON TENTS
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BARNETT EN GI NEERING LTD.
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FCC RE QUIRE MENTS ...................2
1 IN TRO DUC TION......................3
2 SPEC I FI CA TIONS .....................5
3 NO TA TION ........................7
4 OP ER A TION........................8
5 SETUP PRO CE DURES ...................12
6 IN DI CA TORS .......................16
7 CON FIG U RA TION ....................17
8 CON NEC TIONS......................19
9 BOARD LAY OUT .....................20
10 WAR RANTY STATE MENT .................21
11 AP PEN DIX A
OP ER A TION WITH A GE TRUNKING SYS TEM .......22
FCC RE QUIRE MENTS
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This equipment generates, uses, and can radiate radio frequency energy and, if not used in
accordance with the instruction manual, may cause interference to radio communications.
It has been tested and found to comply with the limits for a Class A computer device pursuant
to sub-part J of Part 15 of FCC Rules, which are designed to provide reasonable protection
against interference when operated in a commercial environment. Operation of this equipment
in a residential area is likely to cause interference, in which case the user, at his own expense,
will be required to take whatever measures may be required to correct the interference.
This device was tested using a shielded cable connected to the data port. The unit must be
operated using a shielded cable on the data line, with the shield grounded.
1 IN TRO DUC TION
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The B1474 Radio Modem provides a reliable method of sending 1200 baud data signals over
radio or cable facilities. Digital information is converted to tone format for transmission over
the communication channel. Received tones are converted back to RS232 digital format.
Hardware handshaking using RTS and CTS signals allows the radio channel to be transparent
to the connected equipment. Warm-up and power down delay times required by the radio do
not affect the data signals. Alternatively, XON/XOFF or data buffering may be used where
hardware handshaking is not available.
The communication channel can be a single pair cable, two pair cable or two-way radio.
Conventional land mobile radio equipment can be used or, if specified at time of order, GE
trunking radios may be used.
Power and audio signals are connected to compression terminals inside the modem; the digital
interface is through a DB-25S connector. The B1474 requires 12 to 30 VDC, negative ground,
and approximately 60 mA to operate.
Features available in the B1474 are:
Hard ware or Soft ware Hand shak ing
Either RTS and CTS hardware signals or software XON and XOFF characters can be used to
pause the transmitting station while waiting for the radio system to respond. If short data
streams are to be sent, full data buffering may be used to render the radio system transparent.
RTS/CTS De lay
This adjustable delay allows the radio to warm up before data is sent. The delay is active
regardless of whether hardware handshaking or data buffering is used.
PTT
A low going push-to-talk signal is active whenever the modem is transmitting data.
Squelch De tect
If the radio channel is currently being used, the modem will not return the CTS signal until the
channel is available. If XON/XOFF signaling is selected, XOFF will be returned to indicate a
busy channel; then XON will be issued when the channel is free. (This feature may be disabled
using a DIP switch.)
PTT Drop De lay
This adjustable delay prevents squelch tails from disturbing the received data at the other end
of the system.
Level Se lec tion
Transmit levels are adjustable from 0 to -20 dBm. The receive section has selectable gain of
10 dB, if required, to boost low incoming signal levels.
In di ca tors
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Modem status condition is indicated by front panel LEDs. The LEDs may be disabled to
conserve power.
2 SPEC I FI CA TIONS
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GEN ERAL
Trans mis sion Rate: 1200 Baud (Bell 202 sig naling) or V.23 if fac tory in stalled
Trans mis sion For mat: 8 data bits, no par ity, 1 stop bit if mo dem buff er ing is se lected;
oth er wise trans par ent
Power Re quire ment: Op er ates from 12 to 30 VDC. Cur rent drain is 110 mA with the LEDs on,
65 mA with the LEDs off.
Tem per a ture Range: -30oC to +50oC
Phys i cal Size: Approx. 10" x 5" x 1", in side a metal en clo sure
Ra dio and Wire line: Com pres sion screw ter mi nals lo cated in side the en clo sure
Data Con nec tor: RS232-C com pat i ble, con nec tions avail able through a DB-25S socket
lo cated on the side of the en clo sure
In di ca tors: Power ON, TXD, RXD, CD, RTS, CTS, BUSY
Re ceive Au dio: Sin gle ended, AC cou pled, -30 dBm to 0 dBm
Trans mit Au dio: Sin gle ended, AC cou pled, -20 dBm to 0 dBm
Squelch De tec tion: Sin gle ended, 1M ohm im ped ance, DC cou pled, de tec tion range
0 to 10 volts, po lar ity is DIP switch selectable
PTT: Clo sure to ground for ac tive, 0.5 A @ 50 volts max.
4 Wire Re ceive: Bal anced, 600 ohm im ped ance, -30 dBm to 0 dBm (op er ates full or
half du plex)
4 Wire Trans mit: Bal anced, 600 ohm im ped ance, -20 dBm to 0 dBm (op er ates full or
half du plex)
DIP SWITCH SET TINGS
Trans mit ter Level: -20 dBm to 0 dBm
Re ceiver Level: -30 dBm to 0 dBm
Squelch Po lar ity: Se lects high or low go ing squelch mon i tor sig nals.
Car rier De tect De lay: 5 or 50 msec
As sert RTS: Forces RTS on.
RTS/CTS De lay: 20, 35, 50, 100, 200, 300, 500, or 1000 msec. Al lows the trans mit ter
time to reach full power be fore data is trans mit ted.
PTT Drop De lay: 0, 10, 20, 50, 75, 100 or 250 msec. Keeps trans mit ter keyed long
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enough to en sure squelch tail noise does n’t in ter fere with data at the
re ceiv ing ter mi nal.
Hand shak ing: Spec ifies the type of flow con trol used.
2/4 Wire: Se lects 2 or 4 wire ca ble op er a tion.
LED Con trol: Dis ables LEDs to save power.
Equal iza tion:
Full/Half Du plex:
3 NO TA TION
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Throughout this manual, abbreviations will be used. These abbreviations are explained here for
clarity.
CD Carrier Detect
COS Carrier Operated Switch
CTS Clear To Send
DCE Data Communications Equipment
DTE Data Terminal Equipment
FCC Federal Communication Commission
GND Ground
PTT Push To Talk
RFCTS RF Clear To Send (used in trunking systems only)
RTS Request To Send
SQL Squelch
SW1.8 This signifies a DIP switch. The given example describes the eighth
position on DIP switch number one.
XOFF ASCII 13h sent by a receiving station instructing the sending station
to halt any transmission
XON ASCII 11h sent by a receiving station instructing the sending station
to resume transmission
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