receives digital data from the computer, packetizes it and changes it into audio
tones which are sent out to the radio. The rules the TNC uses to do all of this is
called a protocol.
Protocol for Amateur Packet Radio: AX.25
The most commonly used protocol in amateur packet radio is AX.25. The details
of the inner workings can be found in a book titled “AX.25 Amateur
Packet-Radio Link-Layer Protocol”, which is available from the ARRL. Most
TNC users will not need to or care to go into the details. The TNC takes care of
the nitty gritty work for you, although there are parameters you can set that deter
-
mine how efficiently some of that work is done.
HF and VHF Packet Operation
The KAM’98 may be used for HF packet or VHF packet operation, although not
both at the same time. The KAM’98’s radio port can be cabled to a SSB radio for
HF operation, to a FM radio for VHF/UHF operation, or to a combination
SSB/FM transceiver, such as the ICOM-706.
In each case, the modem within the KAM’98 must be programmed to accommo-
date either HF or VHF packet. Three-hundred baud HF packet is operated in SSB
mode and standard AFSK tone pairs are generally used: Mark 2129, Space 2295.
These are the default tones set within the KAM’98. To switch to 1200 baud FM
packet, the tone pairs - and other packet parameters - within the modem must be
changed. This task can be completed simply by using a set of commands.
+
Some “host mode” Windows programs available from third parties and
Kantronics’ Pacterm’98 for Windows 95/NT/98 set these parameters automati
-
cally for you when you “click” HF packet or VHF packet as a mode of operation.
For reference, these are the recommended parameter values for HF and VHF
packet operation (each of which is set by a command of the same name):
Parameters
HF (default) VHF setting
hbaud 300 1200
mark 2125 1300
space 2295 2100
maxframe 1 4
paclen 64 128
Packet Modes of Operation Overview of Packet Communication
User’s Guide 144 KAM’98 v 8.3
To Next Page
Loading...