Ham Radio/Ham Radio CD-ROM (Emerald Software) (1995).ISO/misc/tn210/tn210.exe/TN210_19.DOC

Text File | 1992-06-28 | 6KB | 99 lines

                                 TN210-19.DOC
                              DUAL-PORT OPERATION
                            ***********************

    This is the method TheNet nodes use to network (gateway) from one frequency
to another.   Two  TNCs  are interconnected via their RS-232  ports.   A  radio
connected to one TNC is on frequency "X" and a radio connected to the other TNC
is on frequency "Y."  Packet traffic intended for nodes on one frequency or the
other will automatically be routed to their destination.

    To  prepare for gateway operation one needs to make sure both TNCs have the
proper  modifications, as discussed below.  Both TNCs should be functional  and
are  working as nodes.  Prepare the special  RS-232  cable wired  as  indicated
in the diagram.    Attach the radio cables to  the  TNCs  (you must provide the
custom   connection for your own radio).     Set  the  audio level  to properly
modulate the radio  (On VHF, MAXIMUM deviation should be  no more  than  3 KHz,
with between 2 and 3 KHz being optimum).   To adjust the transmit tone  levels,
attach  a  terminal to  the Host port.   This sets up  the SYSOP  function when
connected, and  type  K D.      K D sends  an alternating  mark and  space tone
from the TNC  modem through the  attached radio  port cable to the radio.   The
watchdog timer in the TNC will limit the tone transmission to about 12 seconds.
Placing a shunt across TNC JMP 4 will extend transmission time to approximately
22 seconds

    The  TNC audio output gain control is R-76 and is the fourth miniature blue
control  on the right  (looking from the  front of  the TNC)  of the group of 4
potentiometers.    R-76 is a screwdriver  control and is  adjusted  to  set the
desired  deviation level.  HF SSB packet levels are ordinarily set by adjusting
the mic gain for desired power output.     When  finished with VHF  or HF level
adjustments, make a connect to  a distant station or two to verify the node and
radio are  working properly.

    At the rear of the TNC is a dip switch that sets the baud rate for both the
terminal and the radio.  For interconnected TheNet nodes the baud rate is 9600.
The VHF/UHF radios of course are set for 1200 baud.  This means that switches 5
and 7 will be ON, all others OFF.  Connect the special RS-232 cable between the
two TNCs.   Connect  the radio port cables to the appropriate radios.  Turn  on
the TNC  power and you should see the red lights flash on, then off, except for
the power light which stays on.


    It  will take approximately 6 - 10 seconds for the nodes to "initialize" to
each  other and for the gateway to be operational.   This is because each  node
is waiting for a broadcast from the other before each is recognized.  The nodes
will  broadcast within 10 seconds  after being powered on.  If for some  reason
there is activity on the node at the time of broadcast, it is possible this may
interfere with reception of the broadcast.   Should this occur, simply turn the
TNC off, then on, which reinitializes the broadcast cycle.

    Perform the VHF DCD modification to the node TNC.   This allows for quicker
transmit  - receive response  and also helps to avoid collisions.  The DCD mods
will allow VHF and  UHF radios to  satisfactorily  operate unsquelched yielding
even  higher throughputs.   The TNC will only  key up on valid  packets, rather
than  noise.

    If HF node/gateway operation is  planned,  then  the  HF  DCD  modification
should be done to the  HF  TNC.   This gives the same benefits as the VHF mods,
but  is  more elaborate.   It has a THRESHOLD control that needs to be adjusted
to harmonize with HF radio's IF filter.    Other than cut up the TNC,  one  can
insulate the threshold control by wrapping  it with tape and leaving it  inside
the TNC,  once adjusted.   Proper adjustment to HF is to tune the receiver to a
quiet channel just receiving noise.     Adjust the  THRESHOLD control until the
DCD LED just  occasionally  flickers.   It can either be left there, or  backed
off slightly.   This is the optimum THRESHOLD range and, once set, should  hold
true.   The setting of this  adjustment is dependent on the broadness of the IF
filter in the radio.   If the radios are swapped out with ones having different
IF filter  characteristics,  or switched to different HF bands, the control may
need  readjusting.    For  fixed  channel  node work, it shouldn't need further
adjustment.

    Later if it's  decided  to use the  TNC on VHF, it will work fine.  One may
need  to crank the THRESHOLD all the way to the clockwise position to  optimize
its setting.   Even there, the DCD light may not flicker on noise.     This  is
not unusual  since the setting is a function of the VHF radio's wider IF filter
response.

    One  additional  caution:   be  sure  to ohm out  the  TNC  to  radio  port
connections in the cable that comes with the TNC.   Quite often the connections
and the color codings specified in the TNC manual are incorrect!

                        RS-232 dual node cable diagram

           Frame ground - 1 <--------------------> 1 - Frame ground

          Transmit data - 2 <-------.  ,---------> 2 - Transmit data
                                      \'
           Receive data - 3 <--------' `---------> 3 - Receive data

          Signal ground - 7 <--------------------> 7 - Signal ground

      Neg test voltage -10 <---,            ,---> 10 - Neg test voltage
                                |            |
      Data rate select -23 <---'            `---> 23 - Data rate select


    The  above information should be sufficient to get the dual-ported nodes up
and running.