Satel SATELLINE-3AS Guia do Utilizador descarregar pdf (Página 42)

SATELLINE-3AS NMS / NMS Epic / NMS 869 / VHF

User Guide, Version 1.0

6.5

Dual band version

SATELLINE-3AS(d) NMS radio modem is also available as a special "Dual Band" version. The

radio transceiver of the Dual Band version offers two times two MHz frequency bands, and

radio modem can be reconfigured to operate at any channel within those two bands. The

frequency bands are tuned at SATEL manufacturing premises. The maximum separation between

the highest and the lowest frequency can be 12 MHz.

The centre frequency (fc) is set to the middle of the two frequency bands. When using the SL

commands, please note that SL&F=nnn.nnnn is the only command for frequency change which

works in all cases. (SL&+/-=nn command can be used only when the required value for nn

does not exceed 99.)

Max. 12 MHz

Max. 2 MHz fc Max. 2 MHz

Picture 6.2.

Dual band scheme

6.6

Dual channel operation

By setting the Rx and Tx frequencies different to each other the radio modem transmits and

receives data on separate radio channels (although not simultaneously). The radio modem is

initially on the receiving channel. Data flow on the TD line starts the transmitter automatically

and the frequency is changed to the transmitting channel. The delay caused by the frequency

change - before the actual data can be transmitted - is 40 ms, and the same time is needed for

returning to the receiving channel after completing the transmission. The extra delay from a

modem to another is shown below:

Picture 6.3.

Dual channel scheme

NOTE!

SATELLINE-3AS(d) NMS Dual Band is a special hardware version, and the frequency

adjustment is done case by case. Before starting the system design procedure, please

contact the manufacturer for checking the technical details.

Start DATA to be transmitted on TD line of Modem1 End

Normal point-to-point delay (see Appendix B) + 40ms extra delay

due to the Dual Channel o

eration

Start Received DATA on RD line of Modem2 End

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 96 97

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