so i picked up a kenwood d7a-g handheld uhf/vhf transceiver. mostly because it has built-in tnc and aprs. with decent reviews from other folks, seems like a versital handheld. that -- and i'm too impatient to build the tinytrak or pockettracker from byonics. i need a radio anyway - should be a good first all around radio.
the d7a is fairly easy to use, reasonably intuitive -- the features are straight foward as long as you read the manual. there are a few complaints : the battery is lame, it's huge and doesn't hold much power. the stock antenna is bad. again, it's the only ht with aprs built-in. not sure why other handhelds aren't coming out with a built-in tnc/aprs.
one other issue... the manual says not to over charge the nicad battery, but i plan to power it permanently attached to 12v power in my car. not sure about that. guess i'll find out.
anyway, after playing with the radio - the first mission was interface to my gps and computer. i decided to build the custom cables (but you can just find them on e-bay for ~$20). rs-232 is still the de facto standard. i have 2 different gps devices already -- wiring up the unique e-trex interface means not being able to use the magellan, or anything else. for my car, i'm thinking it might be wise to get a gps device w/ antenna i can stick on the roof.
do to this, i dropped by norvac electronics and picked up one 6' stereo 2.5 mm (plug-to-plug) cord, and two db-9 sockets (one jack, one plug, with housing). cut the cord in half -- now you have two 2.5 mm stereo ends w/ wire -- one less thing to do. now just strip the wires and solder up the db-9 connectors... (the radio also comes with one bare 2.5 mm plug & wire).
be sure to mind which db-9 connector you wire to up when attaching the wires to "pins 2 and 3" -- i started out with the wrong one of course... this was in part because the docs i read online didn't make it clear which connector they were actually wiring up -- just said tip to this, ring to that. anway...
wiring :
for the com port : use the db-9 jack (female)
wire the tip, ring (middle) and sleeve (ground) to pin 2, pin 3 and pin 5.
for the gps interface : use the db-9 plug (male)
wire the tip, ring (middle) and sleeve (ground) to pin 3, pin 2, and pin 5.
audio cables tend to use white for tip, red for ring (middle). emptor caveat.
check the photos :
always good to test things out before you screw on the housing (doh!).
alternatively you can build/buy just *one* of these cables, then use appropriate gender changer (to get the right connection) along with null modem connector to flip pins 2 & 3 (the tx and rx wires). means less to carry, but you can only hook up one gps/laptop at a time.
test your work:
activate the plain TNC mode (not packet). hit "pos" for the mypos (my position) screen. once you lock on the satellites and get a fix from the gps, the screen should update showing your coordinates. screen icons (degree, mins, & second) blink when receiving data from the gps. simple??
for the com port you can download a handy configuration app from the kenwood.net to test connectivity. it's a fabulous interface to adjust settings. [flaw: has the old world fixed com port limit (ports 1-4)!]. just connect the cable, and select the appropriate com port, then select "read" from the application menu.
now you're ready to send your position to a digipeater set your radio to 144.390 mhz, turn the beacon on (use "tx interval" & "data tx" settings, say 3 mins and auto). the screen will flash "MY POSITION" when it you receive your own packet back from the digipeater -- so you know it's working. you might try high power mode, and broadcast from somewhere outside for your first test.
update: i bought the bt-11 battery case (adapter), so i'm not charging the nicad battery during use. i leave the battery case empty -- the radio will work at full power with the 12v power adapter - without any batteries (or anything) attached for that matter. this is perfect for the car since the radio always attempts to power-up until physically switched off. [side effect, low power can create a flutter state, on off on off on off (some people question why it does that)]. i also chose a 12v gps with no power switch... i'd rather not have to power up a bunch of gear to bring everything online --just ignition and go.