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Hello Walt,
Here are the specifications of Pax/Pax2 mode
(extract from my help). Go to my help ( Chapter "Modes selection and their
descriptions" for a better presentation).
For how to use Pax/Pax2, there are two
chapters:
"General commands and use of PAX/PAX2 mode and
APRS"
"Description of the specific PAX/PAX2 commands (+beacon/responder/radio mail)" 73
Patrick
PAX/PAX2
Creator : Patrick Lindecker (F6CTE) in
2005
Description :
Baud rate : 62.5 for PAX and 125 for PAX2 Speed : 5.86 characters/sec so 59 wpm ou 11.71 characters/sec so 117 wpm Modulation : FSK 8 tones (3 bits arranged in a Gray form), with a shift between tones of 62.5 Hz (500 Hz bandwidth) for PAX and a shift of 125 Hz (1000 Hz bandwidth) for PAX2. A block is composed of 32 symbols of 3 bits (in other words it is a matrix of 32 columns (following the time) on 3 lines). Each of the 3 block lines of this block corresponds to a character which has been encoded, on a 32 bits vector, using a Walsh-Hadamard transform to provide a high level of redundancy. Note: the implicite used matrix is 64x32 dimension,
the 32 first lines are the 32 standard orthogonal combinations of the Hadamard
matrix. The 32 next lines are their opposite. So any couple of lines are either
orthogonal (scalar product=0) or biorthogonal (scalar
product<0).
Reception mode: sensible to the side (USB or LSB), USB is recommended Shape of pulse : specific shape (between a Hanning window and a rectangular window) Character set : ASCII 6 bits (64 characters) Bandwidth : 500 Hz for PAX and 1000 Hz
for PAX2
Synchronization : automatic using the signal Correction code: no Convolution code: no Interleaving : yes, spreading of 3 bits "vertically" in the block, Scrambling : yes, with a 32 bits sequence
applied on each line of the block but with a delay of 13 bits between two
successive lines.
Drift tolerance : 30 Hz/mn (depending on signal the signal-to-noise ratio) Pmean/Ppeak : 0.76 Lowest S/N : 10 dB for PAX and 7 dB for
PAX2
Note: there are modes directly derived from the 8
tones, 62.5 bauds Olivia mode (Pawel Jalocha SP9VRC) but with a 32 bits vector
instead of a 64 bits vector, a different set of characters and a double speed
for PAX2 (125 bauds). Moreover, any AF frequency (200 to 4000 Hz) must be able
to be used.
Other PAX/PAX2 characteristics:
- the transmission begins with the transmission of the extreme low tone for a time which depends of the value of the parameter TXDELAY and the type of frame (minimum 0.5 second), to be able to manually tune on the frequency, if needed, - the reception and the transmission can be done everywhere on the spectrum, - the search of the PAX/PAX2 central frequency is done when clicking on the spectrum. It takes about one second. Afterwards, when decoding, there is no automatic search but a simple frequency drift following, this to avoid abrupt frequency variations on events as QRM or QSB, - an offset between sound cards sampling
frequencies inferior or equal to 1 % is withstood, but it is hardly advised if
not indispensable to determine the sound card sampling frequency (see
Determination of the sound card RX/TX sampling frequencies). In fact, if the
speed offset is too high, the synchronization could be too long and if would be
possible not to detect the start flags.
PAX/PAX2 protocol in non-connected mode
("Unproto")
All the communication is done through "frames"
(limited set of characters). There is, in non-connected mode, only one sort of
frame called UI, which permits to send either messages or APRS frames. The
Unproto PAX/PAX2 protocol is similar to the AX25 Unproto protocol
(Packet).
Each frame is composed of: * at least 3 flags ("flag": special and unique
character),
* a PID field (protocol identifier) + Version (of the protocol), * a control byte defining the type of frame (UI here), * an adress field: destination then source then possible repeaters (2 max), * a "length" byte giving the number of information characters, * an information field where data is located, * a FCS field composed of 2 bytes where is located the CRC ("Cyclic Redundancy Check Sum") calculation on all the frame data until this field (except flags). A difference between calculated CRC and received CRC makes the frame invalid. Note: the PAX/PAX2 "bytes" are 6 bits long (instead
of 8 bits).
It is possible to pass through 2 PAX/PAX2 repeaters
(with possible use of the alias ECHO).
PAX/PAX2 protocol in connected mode
The connected PAX/PAX2 mode is an ARQ mode type
(ARQ for "Automatic Repetition reQuest" by acknowledgment ACK or
non-acknowledgment NACK) inspired from AX25 (Packet) and Pactor1 but
asynchronous (Pactor 1 being ARQ synchronous) because the acknowledgments and
non-acknowledgments are not done at fixed interval (this possibility not being
available under Windows) but inside a maximum duration.
Each transmitted I frame is subject to an
acknowledgment or a non-acknowledgment by a RR or I frame.
It is possible to pass through 2 PAX/PAX2
repeaters. Without repeaters, the transmission can be "full-duplex" type
(protocol level (OSI level 2)). With repeaters, the transmission must be
"half-duplex" type (protocol level (OSI level 2)), each one in
turn.
This protocol permits free error transmissions.
APRS transmission can also be transmitted.
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Title: PAX2
- [digitalradio] PAX2 John Bradley
- [digitalradio] PAX2 DuBose Walt Civ AETC CONS/LGCA
- Re: [digitalradio] PAX2 Patrick Lindecker
- [digitalradio] PAX2 John Bradley
- [digitalradio] Beacon heard Re: PA... expeditionradio
- [digitalradio] PAX2 John Bradley
- Re: [digitalradio] PAX2 Andrew O'Brien
- [digitalradio] Re: PAX2 Bill McLaughlin
- [digitalradio] PAX2 n4vsd
- Re: [digitalradio] PAX2 John Bradley
- Re: [digitalradio] PAX2 tom noe
- [digitalradio] PAX2 John Bradley
