My GPS hackery
I bought a Kenwood THD-7A handheld radio as soon
as I passed by Technician test. This radio is a great radio to have
if you want to use APRS, and are tired of lugging a TNC, power supply and
cables around with you. I have put my GPS into a new box that allows
me to power it from 12 volts in the car. Here's some pictures of
the box, and the inside of it. The 1/8 jack on the side is for external
power. I built a box to hang off the accessories plug in the vehicle
that routes 12volts out to a 1/8 male plug that I can use to power the
GPS there. I also have a 7ampHr gel cell that I can also use for
power for the radio and the GPS. I am using this for my bicycle rig!
Here's the inside of the box. The GPS board matched the mounting
holes in the box to within about 1/32 of a inch, so I was able to just
screw it down on two corners. I will be adding some support foam
on the other side, toward the middle of the box.
Visible at the top of the picture is the switch that lets me power the
GPS from a 9 volt battery. This turns out to be of limited value
since the GPS draws about 75mah at 9v, and a 9v alkaline has about 180mah
capacity. At the bottom is the external power receptical. This
is a switching receptical, and the CAP is across it to try and keep the
GPS from seeing power loss when the plug is inserted or removed.
This doesn't seem to work, need a bigger CAP! There are diodes
in there so that the 9v battery does not see the external power source
due to the brief contact that makes both supplies present.
My Bicycle APRS Rig
I have a 7ah gel cell battery in my bike bag, and have it wired so I can
plug it into my GPS and my THD-7A. Below are some pictures of the
setup. My dear friend,
KA9MVA, let me use his old 5/8s wave antenna that is on the read of
Here is the bigger picture of my bag and the antenna. Note the
speaker mike on the seat. I can use that for 2m phone...
Here's the Radio Shack Gutter Mount that I found to work perfectly
(well, maybe some bending for true vertical) for mounting this antenna
to my bike.
This is what it looks like inside the bag. There are three layers...
The GPS is on top. The radio is surrounded by foam (the layer on
top of it is removed for this picture), and finally the battery is on the
bottom, also surrounded in foam. You can see the speaker mike plug
in the side of the radio, held on with a rubber band. It slips out
without something holding it in!
My Roll up j-pole antenna
I have also now tried a Roll up J-pole antenna on my bike. It is
made from 300ohm twin lead wire (television antenna wire you can get at
Wal-Mart and elsewhere).
A program called jpole.exe is available that, given a frequency, will
tell you how to make the antenna. Anyway, its benefit is that it
requires no ground plane, so that is why I tried it out. I got the
SWR to 1.00001/1 on 144.390mhz, so that helps with keeping the radio cool!
Anyway, below are some pictures of the antenna taped onto a fiberglass
bike flag that you can also get at Wal-Mart for $5.00.
In the picture below, you can see the twin lead taped to the white fiberglass
poll on the right of center. The coax comes through the plexiglas
restraint assembly to keep the wires on the 300ohm cable from being stressed.
This is very fragile stuff!
In this picture, you can see the mounting to the bike axle. Note
also the stablizing bolt through the metal part of the lower flag assembly,
into the frame. This helps keep the flag from drifting forward or
backward due to wind or other forces (vertical is good, less db loss due
to polarization mismatches).
Finally, this view from the side shows the whole plexiglass assembly.
You can just make out the coax running through it. Sometime when
I have it apart, I'll try and remember to take pictures of the two pieces
that sandwich together there.
I have been surveying some of the more common APRS software packages.
I found them to be interesting, if not useful. However, the majority
of them are written for Micro$oft Windoze, or Windoze CEeeee. I have
not used PalmAPRS, as I am not Palm equipped. I have been writting software
using Java for going on 4 years now, and almost exclusively Java for the
past 3 years. During this time, I have really come to enjoy the freedom
that Java provides from a platform portability point. So, I decided
that I really wanted to create some Java based APRS software that would
allow me and others to quickly put together simple APRS applications without
have to create massive amounts of code and infrastructure just to get started.
- a Java base APRS application development toolkit/environment
One of the more talked about issue on APRS email reflectors has been
software that is currently available. None of us seem to have enough
time to completely support the life cycle of this kind of software.
I would like to find a group of people interested in the portability that
Java provides for UIs as well as smaller devices such as the Dallas Semi-Conductor
TINI, the aJile aJ100 Java bytecode executing processor as well as the
J2ME-CLDC profile available via the KVM on palms.
is my attempt to put together a toolkit that can be used on many different
platforms, from PCs down to embedded Java systems. I want to make
the processing of the APRS protocol disappear from the view of application
writers, and let them just get down to the business of writting the application
they need. This should make it possible for simple applications to
be developed quickly when needed, and for large applications to accept
modules from other applications to make them applicable to another environment,
event or moment.
If you are interested in APRS, or have some desire for a particular
kind of APRS application, check out JeAPRS
and see if it fits the bill for you.
Here's my I-Opener that I got from Netpliance via there Developers
Program. Unfortunately, they failed to do a good job of getting devices
out to people that actually paid for the service (A large number went to
the Linux/Hardware hacker crowd), so this device is not really available
anymore. Netpliance is trying to partner with AT&T and other
service providers now.
This is a 180Mhz PC with 32MB of RAM. They come without a harddrive,
but with a laptop IDE connector (of sorts, see linux-hacker).
I put a 1.3GB laptop drive on this one, and added a Maxim RS-232 on a board
to bring out the second serial port (see the closer picture below, it's
on the left side). I run JeAPRS on it while
mobile, and can stop and type text messages (or let my wife drive while
I operate!), or do other things with it, like change the software, recompile
and see how it works!
Below is a closer up picture. You can see the serial cable comming
out the left side, and just make out JeAPRS on the
screen. The thing is mounted via industrial strength velcro that
is attached to the top of the I-Openers stand, and to my dash. I
just stick the base up on the dash an pound it down to stick. Based
on the way the bars on the stand contact the front of the dash, the pull
is mostly sheer on the velcro. I can then just pop the I-Opener off
the dash, take it inside the house, plug in the USB ethernet, boot it,
and I am on the internet at cable modem speeds off my home network!
I can send files back and forth, synchronize things etc.