Kinky talk

Bill Vodall WA7NWP wa7nwp at jnos.org
Thu Mar 16 14:32:47 PST 2006


I love it when they talk like this...

-------- Original Message --------
Subject: 	Re: [digitalradio] PAX2
Date: 	Thu, 16 Mar 2006 23:23:37 +0100
From: 	Patrick Lindecker <f6cte at free.fr>
To: 	<digitalradio at yahoogroups.com>


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.



     ----- Original Message -----
     *From:* DuBose Walt Civ AETC CONS/LGCA
     <mailto:walt.dubose at randolph.af.mil>
     *To:* 'digitalradio at yahoogroups.com'
     <mailto:'digitalradio at yahoogroups.com'>
     *Sent:* Thursday, March 16, 2006 11:07 PM
     *Subject:* [digitalradio] PAX2

     Well I've looked at the Multiple_PSK for PAX2 specification and on
     the Web and find no description of the mode...how many
     tones/carriers, tone/carrier spacing, baud rate, modulation (except
     I suspect its PSK), etc.

     Without a valid (generally available or advertised) published
     description, operation the modem by amateur radio operators where
     the F.C.C. is the controlling entity is not authorized.

     Someone help me out here.  Where is the specification/description of
     PAX2.

     Walt/K5YFW



     Need a Digital mode QSO? Connect to  Telnet://cluster.dynalias.org

     Other areas of interest:

     The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/
     DigiPol: http://groups.yahoo.com/group/Digipol  (band plan policy
     discussion)


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