MFJ-1270C/1274C MANUAL APPENDIX E: 2400 MODEM
Page 245
MFJ-TNC 2400 PACKET OPERATION
If your MFJ-TNC does not have the 2400 modem, an optional modem (MFJ-
2400) can be purchased and installed. Installation is simple; your MFJ-TNC is
equipped with all connectors necessary to make this installation without
modification or soldering. If you have the MFJ-1270CT or the MFJ-1274CT the
2400 modem is already installed inside the unit.
With the 2400 modem installed, your MFJ-TNC is capable of operating 300,
1200 or 2400 baud packet. The 300 baud and 1200 baud packet modes are not
affected by the installation of the 2400 modem.
The addition of the 2400 modem feature will in no way require any internal
modification to your transceiver.
2400 Packet Operation Setup
All default parameters set for 1200 packet operation can be used for the 2400
operation. 2400 operation needs no unusual setup or parameter changes. There
are however, some changes that can be made later to the MFJ-TNC parameters
which will enable you to improve the speed of the throughput performance of the
2400 operation. The "honing" of the parameters may not seem like much, but
we have found that at 2400, the MFJ-TNC seems to be more responsive to the
TXDELAY, DWAIT, RESPONSE and SLOTTIMES. When using direct
connects and good paths, the MAXFRAME and PACLEN commands can be
increased to allow larger packets to be moved during each transmission. When
returning to the active thru-put frequencies, these two commands should be
reduced to their original settings. You may find that if you were using a TXD of
50, then a TXD of 40 will now perform better. The DWAIT can be shortened or
lengthened to suit the AGC recovery time of your radio. For instance, if you
have been running the DWAIT of 16, it may now perform better at DWAIT of
12 or even 10. The FRACK will appear to exercise more at 2400.
2400 really shows its place in the packet world when used to pass large ASCII,
BINARY and PICTURE files. It is always good to use clear frequency and/or
use direct connects to the target station rather than going thru a node or
digipeater. The reason is obvious. There are few 2400 nodes at the present
time. However, it should be pointed out that implementation of a 2400 node is
just as easy as building and using a 1200 node.
To select 2400 baud packet operation, set dip switch #8 ON at SW3.
The dip swiches 6 ,7, and 8 on SW3 will set as follows for 2400 baud operation:
6 7 8
OFF OFF ON
The MFJ-TNC will be set to 2400 packet operation. The
TURBO
LED will
light. Note that if your MFJ- TNC is not equipped with the 2400 modem, the
TURBO
LED will not function and you will not be able to operate 2400 packet.
B. Receive Audio Setting
The MFJ 2400 modem employs automatic gain control (AGC) for its receive
audio. The receive audio level is pre-set for proper 2400 operation; no
adjustment is necessary in most cases. If you set the receive audio of your
radio properly for 1200 operation, then it will be suitable for the 2400 operation
also. No adjustment for the receiver audio on the 2400 modem board is needed.
