Wavecom W40PC, Manual

Page: 154 / 264

146
•
Transmission Modes WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
FELDHELL
Parameter Value
Frequency range HF
System Synchronous matrix picture telegraphy
Baudrate(s) 122.5 Baud
Modulation CARRIER KEYING AM
Receiver settings CW, LSB or USB
Signal source(s) AF, HF or IF
Feld-Hell is a synchronous picture telegraph system invented in the 1930s. It is using a virtual
matrix laid down on the character to be transmitted. The pixels of the matrix is then sent,
scanning the matrix from the bottom of the first column (left) to the top of the last column
(right) covering a matrix 7 columns x 14 lines. The first and last columns are blank as are the
top and bottom lines giving an effective matrix of 5 x 10 pixels. Pixels are always sent in pairs.
The original Hell system was a very simple mechanical one with a indented wheel for each
character used to generate the transmit pulse trains via a contact.
In the receiver the pulses activated a printing magnet with a writing edge, which pushed a
paper tape towards a helix inked by an ink roller.
No means of synchronization besides of nominal helix speed was used. Speed differences
showed up as raising or falling lines of letters, but as the pitch of the helix was designed to
print a double row of characters, one complete character would always be displayed on the
tape.
Hell utilizes AM in the form of CW or A2. When receiving Feld-Hell the decoder will emulate
the original Hell tape printer and print each character twice making exact phasing unnecessary
as at least one character will be complete and unbroken.
By selecting “122.5 Baud” or “Variable rate” reception is started. Selecting “Polarity” will
determine normal or inverse screen color.
In the “Demodulator” submenu the special function fields “AM-Gain” and “AM-Offset” are
placed. Centering of the signal deviations on the bar graph is controlled by adjusting “AM-
Offset”. In addition maximum deviation is required on the bar graph. This is done by adjusting
“AM-Gain”. It should be noted that these two adjustments are influenced by each other.
Right-click on the image to open the zoom menu where the image can be zoomed in and out.
FLEX
Parameter Value
Frequency range VHF
System PAGER
Baudrate(s) 1600, 3200 Baud
Modulation DIRECT-FM
Receiver settings FM, 15 kHz
Signal source(s) HF or DIS
Alphabet ASCII
FLEX is another mode used for pager transmissions. It is often combined with POCSAG and
GOLAY.
FLEX specifies 4 different transmission modes: