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The single frequency node is the most popular type of Packet Radio Network node.

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The "GATEWAY" node shown here provides links between VHF/UHF frequencies and/or baud rates. By utilizing the "diode matrix" shown on another page, the System Node Operator (SNO) can establish several nodes into a "node-stack" that will link many frequencies, baudrates, and LANs. Most node stacks are limited to four nodes or less.

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Schematic to add squelch to the MFJ-8621 Packet transceiver

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This schematic illustrates the jumper settings for 1200 and 9600 bauds in the MFJ-8621 Packet Only transceiver.

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This drawing illustrates the jumper placement on the bottom of pre-1991 TNC2 & clone PC boards.
This mod is necessary when the TNC is used in a node-stack (gateway, or multiport configuration).

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Wiring pictorial to illustrate how two (2) nodes with 25 pin RS-232 ports are interconnected. Note that both TNC/NODES should have the DIP switches (or internal jumpers) set for the same 232 port speed. The DIP switch settings of the radio data speed is set according to the internal modem speed.

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Alternate gateway interfacing when using TNCees with different RS232 comports; eg; DE9 to DB25 connectors.
NOTE: the installation of jumpers on each connector. Both TNC/NODES must have the data comports set to the same baudrate.
The datarate is usually set to 9600 bauds. Note also that the TxData and RxData lines are rolled end to end; eg; TxD to RxD and vice versa.

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Wiring pictorial to illustrate how two (2) nodes with 9 pin RS-232 ports are interconnected. Note that both TNC/NODES should have the comports set for the same 232 port speed. The DIP switch settings of the radio data speed is set according to the internal modem speed.

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This drawing enables two (2) nodes/TNC's to operate into one (1) radio. A node and a TNC, or a TNC and CONVERS node, or a CONVERSE node and a TheNET node.

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Schematic of a 4-node stack, diode matrix.
This diode matrix enable stacking several
X-1J4 TheNET nodes into a "node-stack."

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Schematic of a 3-node K-NET stack, diode matrix.
This diode matrix enables node stacking the Kantronix KPC-3, KPC-3 PLUS, KPC-9612,
and KPC-9612 PLUS with the Knet EPROM option installed.

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This simple circuit(s) enable two (2) TNC or KPC to be connected to one (1) radio. The interconnect diodes prevent both TNC/KPC from activating PTT at the same time. The diodes are 1N4001.

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The pictorial above provides help when installing the "CONVERS" EPROM into the TNC2.
The results are a CONVERS node. These type nodes should only be used on a non-throughput
frequency. CONVERS nodes are known to cause heavy Packet congestion and collisions.

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Although DRSI no longer builds this TNC, there are several still around. This illustration shows how the DRSI DPK-2 and DPK-9600 TNC's are modified to become an X-1J4 node and/or gateway. The EPROM must be X1J-4 code that is specifically written for the TNC2 TNC's.

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This modification applies only to the MFJ-1270C REV "10" to an X-1J4 node. The EPROM must be X1J-4 code that is specifically written for the TNC2 TNC's. PLEASE NOTICE the five "NOTES" that indicate the changes to the MFJ-1270C "revision 10."

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The modification of the MFJ-1270C REV 11 to an X-1J4 node. The EPROM must be X1J-4 code that is specifically written for the TNC2 TNC's. Complete instructions are provided in the FREE Packet handbook discussed below. Be sure to specify the MFJ TNC node handbook.

The following steps outline the procedures to transform the MFJ-1270C REV 11 (shown in the above photo) into a

1. Remove jumper from all pins of JMP 9.  Jumper will be used later in 
   this modification at JMP 21.
 
2. Remove IC U40.  After the modification is complete, place U40 into a plastic wrapper 
   and tape inside the front face-plate for later use if the node is ever returned to 
   normal TNC service.
 
3. Remove jumper from JMP 15.

4. ADD A JUMPER at JMP 16 (use jumper from JMP15).  

5. ADD JUMPER at JMP 21 (use jumper from JMP 9).

6. Remove the TNC (stock) EPROM at IC location U23.  CAREFULLY install your 
   new X-1J4 EPROM into socket at U23.  BE SURE ALL PINS ARE INSERTED INTO THE SOCKET 
   (be sure there are no bent pins).  Pin number 1 is NOT left out of socket as it was 
   with  earlier revisions of this TNC.  This modification applies only to MFJ-1270C 
   "Rev 11."

7. Cut trace at JMP "X" Notice that tiny traces are close to JMP X:  DO NOT CUT any 
   other trace.  Cut ONLY the trace between pads of JMP X. Use extreme caution when 
   cutting.  

NOTE "A": The photo shown above is an MFJ-1270C/Rev 11, and has the "MFJ-9600," (9600 baud)
   internal modem installed.  The same mods apply to both 1200 and 9600 baud MFJ-1270 "C's."
   


NOTE "B": Cutting JMP "X" is optional; If you are concerned with the node hearing 
   itself and listing its own call and alias in its own node list, then CUT JMP "X".
   A problem occurs when JMP "X" is NOT cut and the node lists itself in its own node 
   list.  A user might inadvertently issue a connect request to the same node and 
   find that they are connected again (locked) into the node.  They may be required to 
   issue the "BYE" command two times to be released.
   


NOTE "C" All MFJ-1270C/Rev 11 built after July 1996 have R14 & R15 installed.  If they 
   are not installed in your MFJ-1270C/Rev 11, they will not cause a problem unless you 
   plan ot use the TNC in a node gateway, between two frequencies or in a node stack with 
   a diode matrix.  If R14 & R 15 are missing and your node IS TO BE USED between two 
   frequencies or in a node stack with a diode matrix, then you should continue to steps 
   8 and 9.

8. If TNC is to be used as a GATEWAY between two frequencies or baud rates, insure that 
   R14 & R15 are installed.  If they are not, remove the PC board and add R14 and R15.  
   R14 and R15 are 100 ohms @ 1/4 watt each.
 
9. To remove the PC board, remove the front face-plate (2 screws), then remove the screw 
   that attaches Q3 (regulator) heat-sink to the front of the TNC.  Next remove the four 
   (4) screws which hold the PC board in place. The locations of the screws are shown in 
   the photo as a red circled "X" symbols.
 

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Add some class to your network by installing the MFJ-52B into the node. This add-on PCB enables the network user to read the deviation of their radio when connected direct to the node. A similar mod/add-on may be applied to the PacComm TNC's. The DEViation PC Boards, wired and tested are available from MFJ or PacComm. Complete documentation is included with the PCB. The node EPROM code must be the X-1J4 TNC2 version.

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When ordering the add-on MFJ-9600 MoDem, be sure to specify revision 1.4 or later.
Version 1.4 has Gated TX & Rx Eproms plus other enhancements for better operation.

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The drawing shown here illustrates the modifications that I use to build the MITREK(tm) into a 9600 baud, data-ready transceiver. Note; TXD may be set as low as 15 (150 milliseconds); These radios run between 40 & 70 watts output and additional TXDelay allows the radio to reach full power output. The SEDAN has more than 50 of these radios in service on the SEDAN 6 meter backbone at 9600 bauds and the TXDelay of 17 is no problem. A connect from Central Virginia to Atlanta, Georgia (600 + miles) is made in less than five (5) seconds.

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Converting the PacComm Tiny-2 Mark 2 to an X-1J4 node.

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CLICK HERE FOR EPROM FORM AND PURCHASING INFORMATION!"