Wavecom W61PC V7.5.0 - Manual (Page 183)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  173
displays the user data in BINARY, HEX, ASCII ASYNC, ASCII ASYNC (7 Data bits and 0 Stop bit) or
ASCII SYNC format which may be selected from Options/Message Type.... The decoder stops display-
ing data after the EOM bit pattern is received.
In the HEX display mode, the decoded binary data is just displayed as is, MSB first. Display is terminated
when more than 25 NULL hexadecimal characters have been received.
In ASCII ASYNC mode, the bit stream is searched with an ASCII ASYNC structure, i.e. one start bit (0), 8
data bits and at least one stop bit (1). The 8 data bits are transmitted LSB first. In addition to the EOM
pattern, the display will stop if more than 300 NULL characters are received or if the async data structure
is violated more than 80 times.
In ASCII ASYNC (7 Data bits and 0 Stop bit) mode, the bit stream is searched with another ASYNC
structure, i.e. one start bit (0), 7 data bits. The 7 data bits are transmitted LSB first. In addition to the
EOM pattern, the display will stop if more than 300 NULL characters are received.
In ASCII SYNC mode, each 8 bits (LSB first) represent one ASCII character. The display will stop if the
EOM pattern is received or if more than 20 NULL characters are received.
Tuning the decoder
The decoder processes the signal in both SSB settings: USB and LSB. The sideband can be selected with
the Polarity option in the menu: NOR means USB and INV means LSB signal.
The center frequency of the decoder should be set to 1800 Hz when the receiver is correctly tuned to the
sending station. Small frequency variations are automatically compensated for in the decoder. The center
frequency of the decoder can be adjusted to ± 400 Hz from its normal setting. By using the bar graph,
any remaining frequency difference can be compensated for by fine-tuning of the receiver frequency or by
adjusting the center frequency of the decoder.
MIL-188-141A
MIL-188-141A Standard, also known as Automatic Link Establishment (ALE), specified by the US Depart-
ment of Defense in September 1988 and with two Change Notices in June 1992 and September 1993, is a
procedure whereby radio stations are able to automatically set up their link thus eliminating the need for
skilled operators - in fact the growing lack of trained and experienced staff was a driving force behind the
idea of ALE.
In March 1999 MIL-188-141A was integrated into the new specification MIL-188-141B, Appendix A. The
message protocol was thereby extended slightly.
Parameter Value
Frequency range HF
Operation modes Broadcast/Simplex FEC
Modulation MFSK-8
Symbol rate 125.0 Bd
Center frequency 1800 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
A station will transmit a link quality burst which may or may not contain the address of another station on
a series of pre-assigned frequencies. The listening station(s) will continuously scan through these frequen-
cies. During scanning the receiving station will perform a link quality analysis and measure signal to noise
ratio and bit error ratio. These measurements are used to set up a table in memory of link quality assess-
ments for each station and frequency.
Based on the values of the table, the best frequency available is selected when the station wishes to
transmit. When the ALE controller of a receiving station hears its own address (or the address of the group
to which it belongs) it will stop the scanning and respond to the call. The stations will then either switch to
a low speed data exchange mode or to a high speed data (FSK or PSK) modem or to voice mode.