4-Level FSK Modem Data Pump
Page 31 of 50
MX929B PRELIMINARY INFORMATION
4.6.1.5 Interleaving
The 66 symbols of a 'Header', 'Intermediate' or 'Last' block are interleaved by the modem before transmission
(and before the ‘S’ symbols are added) to provide protection against the effects of noise bursts and short
fades. The 22 symbols of a ‘Station ID’ Block are not interleaved.
In receive mode, the MX929B strips out the 'S' symbols and then de-interleaves the received symbols. FEC
and decoding follow.
4.7
Transmitted Symbol Shape
Bit 4 of the Command Register (TXIMP) selects the transmit baseband signal and the receive signal
equalization as follows:
If the TXIMP bit is '0', then the transmit baseband signal is generated by feeding full-symbol-time-width 4-level
symbols into the RRC lowpass filter and the receive signal equalization is optimized for this type of signal.
With this setting, the MX929B is compatible with the MX929A device, another member of the MX929 device
family.
If the TXIMP bit is set to '1,' impulses, rather than full-symbol-time-width symbols are fed into the RRC filter
when in TX mode and the receive signal equalization is suitably adjusted in RX mode.
TXIMP = 0
TXIMP = 1
+3
+1
-1
+3
+1
-1
-3
-3
1 symbol
time
1 symbol
time
Figure 16: Input Signal to RRC Filter in Tx Mode for TXIMP = 0 and 1
Figure 17: Tx Signal Eye TXIMP = 0
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