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Packet radio projects (including APRS)

Presentation "APRS Packet Digipeating via the ISS"

PDF - 46 pages (~ 1.6 MB)
ODP - OpenOffice source document (~ 800 KB)
February 11, 2009, Rev. 6

Permission granted to distribute, modify, and/or pilfer - provided appropriate credit is given, thanks!

This presentation was given at:
Am Tech Day @ SLAC, March 2008 & January 2009
Radiofest in Monterey, CA, March 2009

OpenTracker+ (OT1+) modification

OT1+ mod motivation

My OT1+ serial port was flakey due to excess liquid solder flux (that was conductive) being trapped between the microcontroller socket and the PCB. (This was a kit I soldered myself.)  Before discovering this, I made modifications to debug the issue.

The main motivation for the modifications is that I spent quite a bit of time debugging why the serial interface would work on and off.  Sometimes the OT1+ would beacon normally for a few minutes, then no beacon and no OT1+ GPS lock blink.  Once in that mode, even the PC could not connect to it.  After powering-off the unit for awhile, it would sometimes work again.  I suspected the Q2 2N7000 FET was being blown.  So I added additional circuitry to protect the FET input from static damage, among other paranoid enhancements in other parts of the design.

After 3 weeks of debug, the problem turned out to be excess liquid solder flux underneath the microcontroller socket near pin 13 (serial data in).  The flux caused a low resistance path to adjacent pins or to ground - with a resistance of 1K ohm to ground measured at socket pin 13 (with the microcontroller removed).  An oscilliscope on pin 13 showed a voltage swing of less than 2 volts (with GPS unit attached) - no wonder!  After removing the flux underneath the socket with a solder flux wash chemical, the resistance changed to 5K ohms to ground - resulting in a full 5 voltage swing at pin 13.  Serial port issues resolved!

I'm sure that Argent Data would not recommend these changes.

Someone suggested that using rosin core solder probably would not have these issues.

Peter  AF6DS    Oct. 2009

OT1+ modification schematic:

To prevent GPS super-cap reverse surge (when source power is removed or shorted), thus protecting the LM7805 voltage regulator and microcontroller. The R11 value was changed from 10K to 3K ohm to provide better serial port levels to the microcontroller. Additional protection circuitry added to the serial port input FET for static and over-voltage. RFI reduction, with 10K pullup resistor, to Transmit Now.

A GlobalSat BR-355 serial GPS receiver (+/- 5V RS-232 voltage swing) is being used with the Argent Data Systems OpenTracker+.

OT1+ modification photo:

Surge protection diodes soldered in on top of the LM7805 voltage regulator, low-voltage drop Schottky diode "jumpered" onto +5V and Vext on JP1 (pins 6 and 8), Transmit Now 10K pullup to +5V, 3K @ R11, serial port protection circuit.

Earlier modification photo:

OT1+ COR_In 10K ohm pulldown:

To prevent false CD prior to FW 54908, using 10K 0805 size SMT resistor (photo and modfication schematic shows old value of 1.1K ohm).

Sample OT1+ / OTUSB  .cfg file (programming via otwincfg.exe)

Tethering a null modem adapter:

With a cable tie that is secured inside a hole drilled in the OT1+ case - so you can find it when you need it for PC programming.

Yaesu interfacing (to OT1+):

HT (e.g. VX-6R) - interface capacitor recommended value change (from 10uF to 0.1uF).

Mobile (e.g. FT-8900R) cable wiring diagram and notes.

Yaesu FT-xx00R to OpenTracker+ (OT1+) cable wiring

OpenTracker+ (OT1+) to Yaesu FT-7900/8800/8900R TNC cable wiring
AF6DS  Sept. 19, 2010

Male connectors are used on both ends of the cable.  The wiring is for 1200 baud operation, typically used on 2 meters.

OT1+: DB-9              Yaesu: "PS/2-type" 6-pin DIN
pin# / desc             pin# / desc
----------------        ------------------------
 1  TXA (out)     <-->   1  PKD/DATA IN  (10K ohm imped, 40 mV p-p max in)
 5  RXA (in)      <-->   5  RX1200  (10K ohm imped, 300 mV p-p max out)
 3  PTT (out)     <-->   3  PTT  (ground to transmit)
 6  GND           <-->   2  GND
 2  COR/SQL (in)  <-->   6  PKS/SQL  (open/unmute: +5V, closed/mute: 0V)

Yaesu Data DIN female connector pinout (looking at back of transceiver):

   PKD/Data In  --- 1   2 --- GND
          PTT  --- 3     4
         RX1200 --- 5 | 6 --- COR/squelch

   [Yaesu's RX1200/RX9600 signal names should really be TX1200/TX9600?]


  OT1+ hardware:
    - set jumper on 'HI', not 'HT' (transmit audio level for mobile use)

  OT1+ programming (via otwincfg.exe):
    - check box: External Squelch  (uses the transceiver's squelch line) [the wiring diagram in Yaesu FT-xx00 user manuals does not show the squelch connection being used, but it is used in this case]
    - do not check: Invert Carrier Detect  (Yaesu has active high squelch)
    - do not check: Software DCD  (use the squelch line detection instead)
    - Tx Audio Level slider bar position: (1/2) midway between min and max [audio level not measured with meter, but checked tracking on aprs.fi]
    - increase Tx Delay to 400 mSec, to allow time to switch to the Main band during transmit if the other band is actively receiving

  Yaesu FT-8900 specifics:
    - the FT-8900R default setting is to receive on the Main band (menu item #27, PCKT B), and transmits only on the Main band
    - make sure baud rate is set to 1200bps (menu item #26, PCKT S)
    - set Squelch level to be just above the noise such that weak stations can be detected by OT1+ (otherwise OT1+ will not know there will be a collison)
    - Volume control knob does not have any effect on the data port signals, e.g. it can be turned all the way down and channel busy/carrier detection will still work
    - make sure WIRES mode is not active (toggles by depressing lower-left knob)
    - set Audio Mute mode to Tx [menu item #24, MUTE], to mute "Sub" band audio during Main band transmit (optional?)

Packet TNC / radio interface cable wiring (to Kantronics KPC-1 & KPC3+)

Motorola MCS 2000 / KPC3+:

Motorola MCS 2000 to Kantronics KPC3+ TNC cable wiring

Motorola MCS 2000 - Kantronics KPC-3+ TNC packet cable

AF6DS   1/25/2009

 Female connector              Male connector           5 cond wire
 DB-25 (MCS 2000)              DB-9 (KPC-3+)            color
 ----------------              -------------            -----------
 Fixd Rx  pin 11  <--------->  pin 5  Rx Audio          green
    == or ==
 Spkr +   pin  1  <--------->  pin 5  Rx Audio          [not used]

 Spkr -   pin  3  <--------->  pin 6  Gnd               black
 Alg Gnd  pin 10  <--------->  pin 9  Gnd (Mic)         brown

 Mic      pin 23  <--------->  pin 1  Tx Audio (Mic)    red
         (pin 13 ?)
 Dtl Gnd  pin  4  <---+----->  (cable shield, but       braid /
                      |         no KPC-3+ connection)   shield
 Emergcy  pin  9  <---+
 PTT      pin 21  <--------->  pin 3  PTT               white

 Note:  RC network not required for mobile units, only HTs.


Yaesu / KPC3+:

Yaesu FT-series to Kantronics KPC3+ TNC cable wiring

Yaesu FT-7900/8800/etc to Kantronics KPC3+ TNC cable

KPC3+  DB-9 male        CT-39A 6-pin DIN male
pin# / desc             pin# / desc / wire color
----------------        ------------------------
 1  TXA (out)    <--->   1  Pkt In    black
 5  RXA (in)     <--->   5  Rx 1200   yellow  (10K ohm imped)
 3  PTT (out)    <--->   3  PTT       red
 6  GND          <--->   2  GND       brown

Yaesu Data DIN connector looking at back of transceiver (with the CT-39A wire colors shown in parenthesis):

  Data In (black) --- 1   2 --- GND (brown)
       PTT (red) --- 3     4
  Tx 1200 (yellow) -- 5 | 6

Note:  The Yaesu FT-7900 and FT-8800 manuals have the CT-39A wire colors are specified incorrectly in the wiring table (but the wiring diagrams are correct), and they do not match actual cable wiring nor the wiring label on the CT-39A package.

ICOM IC-228H / KPC-1:

ICOM IC-228H to Kantronics KPC-1 TNC cable wiring

Kantronics KPC-1 - Icom IC-228H TNC packet cable
AF6DS & KA4PNC   5/24/2009

 Male connector                Female connector         5 cond wire
 5-pin DIN (KPC-1)             8-pin DIN (IC-228H)      color
 -----------------             -------------------      -----------
 AFSK       pin 1  <-------->  pin 1  Tx Mic In         black

 Rx Audio   pin 4  <-------->  pin 8  AF Out            white (but
                                                        not required)
 Gnd        pin 2  <---+---->  pin 6  Gnd (Mic)         brown
                       +---->  pin 7  Gnd (PTT)         green

 PTT        pin 3  <-------->  pin 5  PTT               red

  - Cable shield is connected to 5-pin DIN metal housing.
  - Use separate mono audio cable from IC-228H Ext Spkr to KPC-1 Aud In.