The Papakura Amateur Radio Club has been fairly active with technical projects in 2008.  The project for the last quarter has been assembly of OpenTracker kits using PCB's and component kits supplied by Keith ZL1BQE and Ian ZL1VFO.

The plan in early 2009 is to combine the assembled OpenTracker boards with Maxon DM-2550 radios and a GPS/Radio interface board developed by Keith and Ian to form a self contained APRS unit.

There was plenty of enthusiasm for the project.... so much so that we ran out of PCB's.... so I built my OpenTracker using a DSE Prototyping board... a little more time consuming but not difficult and a good way to better understand the circuit.

My plan was to package the OpenTracker, Maxon, GPS, Interface circuits and battery into a rugged and easy to carry unit that I would move from car to car and at least one take flying in the Citabria or Cub.  Surfing the net for packaging ideas I noticed a few articles where projects had been packaged in used ammunition cans.

New Zealand is not a great place for Army Surplus but I tracked down 30 calibre boxes (and larger) at Kiwi Disposals in Karangahape Road for NZ$12.50. Good condition.... a little disappointing that they were labeled as containing blank rounds but you can't have everything.  

I must at this point mention that I am not an experienced metal or woodworker.... do the approach I took was very much influenced by my limited selection of tools and availability of easy to work materials.

I wanted to make a slide in/out module that would fit into the can and hold the following items securely:

    1 x Maxon DM-2550 Data Radio
    1 x Radio / GPS / Power Interface board
    1 x Ashtech G-8 GPS Receiver Module
    1 x OpenTracker Module
    1 x 12v SLA Battery
    
A 30 calibre looks like quite a big box before you start trying to package everything inside!

I also wanted the top panel to be recessed sufficiently that the box could close without hitting the RF Out, GPS Antenna connectors and other switches.

So my solution was to start with a $4.00 kitchen cutting board from The Warehouse.  

This had some nice features.....

    A handle.
    Easy to cut, file and generally shape as required.

But it wasn't perfectly flat... as you may notice in the photos.
     
I cut it to size to form a base board and front panel and joined these with some 90 degree aluminium brackets that were sitting on the workbench (no idea why I had these... must have been for another never completed project).  I need some sealant between the base board and front panel to hide the bend in the baseboard.

Played around with spacing of the various components to see where they could fit.  The final placement was really determined by the battery and Maxon as the two largest components.

The interface board was mounted above the Maxon.  This is not the Keith/Ian special but provides

    11.7 volts to the Maxon using an LM317
    5v to the GPS module using an 8221L switching regulator
    RS232 level conversion of the GPS TTL in/out so the OpenTracker understands the data
    3v Memory Backup battery for the GPS
    A mounting place for the OpenTracker board
    
The Ashtech G-8 GPS module is one I got from Derek Fortune Zl1UF a few years back. 

Not as small and thrifty on power as the newer units but seems to work well enough for this application.  The main issue with the G-8 is in the default configuration the RMC NMEA message is not enabled so the OpenTracker will not get a position lock. 

Enabling this is easy enough with a PC (and the correct documentation) but the configuration change is lost as soon as power is removed... unless a backup battery is fitted.  It will be interesting to see how long the battery lasts.... it if proves to be a problem there is enough space on the board to fit an 8 pin Micro with software to configure the GPS on power up.