Wavecom W61PC V7.5.0 - Manual (Page 209)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  199
PICCOLO-MK6 is based on the ITA-2 Baudot alphabet. 6 tones are used which results in a total of 36 com-
binations. The tone duration is 2 x 50 ms for one character which corresponds to 75 Baud Baudot with 7.5
bit code words.
PICCOLO-MK12 transmits ITA-5 characters. To transfer 7 bit ASCII characters, twelve tones are required.
This produces 144 bit combinations of which 128 are used. The transmission speed is equivalent to an
asynchronous data rate of 110 Baud.
The WAVECOM software displays four windows on the screen: Normal T1/T2, Inverse T1/T2, Normal
T2/T1 and Inverse T2/T1. This way of organizing the display is due to the fact that it is not possible for
the operator to decide from the monitored tone sequence, whether the first received tone constitutes tone
1 or tone 2 of a character. In addition, reception may occur using either the upper or the lower sideband
giving a total of four decoding possibilities. Decoding of data is done simultaneously in all four windows.
Tone Assignment of PICCOLO-MK6 and PICCOLO-MK12
The decoder or receiver must be tuned to obtain the midpoint between tones 5 and 6 as the center fre-
quency. In the case of IDLE (standby) transmissions these two tones are keyed at a rate of 100 ms and
tuning becomes quite simple.
Decoding of PICCOLO and COQUELET systems requires receivers with high frequency stability. Thus state-
of-the-art receivers using PLL or DDS frequency synthesis are well suited for the reception of these sys-
tems.
The software also provides an AFC (Automatic Frequency Control) function. Frequency deviations are con-
tinuously monitored by the software and automatic correction is introduced. The control range is ±5 Hz.
The AFC function may be enabled/disabled using the Demodulator menu.
The MFSK demodulator is intended for use with MFSK systems. This mode may be selected in the De-
modulator menu via the Mode item. The center frequency should be set to approximately 1700 Hz.
One manufacturer has doubled the data transfer rate and shortened the tone duration to 2 x 25 ms. this is
equivalent to a transfer rate of approximately 150 Baud Baudot with 7.5 bit codeword. The standby tones
were also changed, but otherwise the systems are identical.
Almost all transmissions in PICCOLO-MK6 and PICCOLO-MK12 are encrypted. However, some stations
transmit meteorological data and operator communication in clear.
POCSAG
The pager services introduced by a number of PTT administrations use the POCSAG (Post Office Code
Standard Advisory Group) standard. Pagers are one-way devices. A base station controls a large number
of receivers and a return channel for transmission of reception acknowledgements or text is not available.
Parameter Value
Frequency range VHF/UHF
Operation modes Simplex pager
Modulation FSK
Symobol rate 512, 1200 or 2400 Bd