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; Packet Radio "The Basics"
Section 1
MHeard
If enabled, the heard list shows the last few stations
heard. The number of entries is limited and set by the
sysop so any stations not heard for a while may get
pushed out of the list by others heard.
Assuming that a station is not pushed out in this manner,
the display shows the number of packets heard from that
station since it appeared in the list and the time since it
was last heard. The time is hours, minutes and seconds.
The list also shows the port on which the station was
heard (port 0 is the radio port), and if it hears IP frames
or Net/Rom frames, it adds a note to show that the station
is a node and/or a TCP/IP station.
If the list is long enough so that a station is not heard for
12 hours, it will get deleted anyway.
The list may also show a column headed 'Dev.'. This will
only be present where the sysop has added to the node a
small hardware add-on that measures the received signal
audio level. Specifically, it gives an indication of the
peak audio level.
By means of a software configuration control and prior
calibration, this gets converted into an indication of the
transmitting station's signal deviation. It does this by
sampling the audio level after every valid packet.
Care must be taken over its interpretation. It does not
measure independently the two tone levels - it is assumed
that whatever local standards that relate to pre-emphasis
(i.e. use it or not) have been implemented.
PACKET
MODULATION
IMPORTANT:
The 1200 baud Packet modulation / deviation is
important. In contrast to the 5 KHz deviation of VHF
FM voice, Packet modulation should be set to, or just
below 3 KHz.
Often, packet stations are set up, and the audio level
tweaked until it appears to work reasonably error free.
The idea of this add-on is that, having done that, you
then connect to the node and display the heard list to see
an indication of your actual deviation. It may then be fine
tuned to set it correctly. Local advice must be taken over
the correct setting as it depends on the channel spacing
being used ( e.g. 12.5, 25 or other KHz ).
Section II
"2 N 1" Handbook
The Packet Radio
Section 2
DEFINING A FEW OF THE X-1J4 FEATURES:
/
DEVIATION
; TheNET X1J4 System Node Operators Handbook __ Page 21
Buck Rogers K4ABT
by
; The X1J4 System Node Operator's (SNO) Handbook
The METER command is set ON, or made active by the
sysop when the system manager sets the meter command
to a value other than 0 (zero). He enters the command
mode using the password and then sets the sysop
"METER" command to a number above 0 (zero) and
below 256.
The sysop first calibrates the deviation meter within the
node while it is on the work bench before installation at
the node site. Setting the METER command to 0 (zero)
will turn the deviation feature OFF.
Provided the meter is calibrated according to the sysops
"DEVIATION" manual, the sysop might set the METER
command to 20. Thus the reading would be multiplied
by 255, and equate to about 5 KHz for full scale reading.
METER 10 would therefore support a reading of 2.5 KHz
full scale. eg; 10 X 255 = 2550 Hz or 2.55 Khz.
Once he has put the node at the final site, the METER
command may be used to tweak the DEVIATION for the
final reading that corresponds to the deviation from a
known source.
ONCE THE DEVIATION Analog to Digital Converter is
installed into the TNC, and calibrated, the receiver
volume should not be moved! To change the input to the
ADC will cause erroneous readings for users of the DEV
X-1J node.
In addition, the deviation reading will give the wrong
answer when the following conditions exist:
•
If the transceiver modulation contains too much
IS
distortion.
•
If the transceiver too far off frequency.
The list of features in the X1 node is too long to cover
here, however you can find a full explanation of the X1
node in the August and September 1993 issues of CQ
magazine.
In addition, the new X1J release 2 node has added the
Voltage meter, the "S" meter, and Temperature sensor
to the node firmware.
The sysop can easily install this feature filled PC board
add-on.
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