Category Archives: Amateur Radio

Ham Radio – Studying for the General Class Exam

When my renewal notice came in the mail, I was surprised to learn that I’ve had my ham radio license for just over ten years.

I received my Technician class license in college shortly after my classmate Tony introduced me to the world of amateur radio.  I started out playing with TNC‘s and packet radio.   Later, with Tony’s help, I built various microwave radios so I could participate in the very active San Diego Microwave Group.  Some of my projects included a 10GHz transverter and a simple 24GHz wideband radio that used a surplus gunnplexer as an RF source, the same kind as found in police radar guns and many automatic door openers.  (Please excuse my ancient webpages, they were cool ten years ago, ok?)

Here I am with my 10GHz transverter in the summer of 2000 during the ARRL 10GHz and Up Contest.

10GHz Transverter
Sun, sand, and microwaves in Santa Barbara.

I also used to be somewhat active on 2m/440 and still have the Kenwood TH-79A radio my Dad bought me after I got my license.  I still use it today, but not for voice communications.  It has a new life now as part of my APRS Tracker project.

After seeing how many hams there were at NOTACON earlier this year, I finally decided it was time to upgrade my license to General class.  This will give me more operating privileges on the HF bands, the traditional low frequency / long distance communication bands that are most commonly associated with amateur radio.  My goal is to set up an HF station at home and maybe start playing with a Software Defined Radio system such as GNU Radio with custom homebrew hardware.

Before my trip to HAR I picked up a copy of the ARRL General Class License Manual and printed out a list of VE sessions in the Bay Area over the next couple of months.  Now that I’m back, it’s time to start studying!

APRS Tracker

APRS Tracker

This week, my brother is relocating from the San Francico Bay Area to Texarkana, Texas.  I’m helping him move, so for the next two weeks we’ll be on a road trip through California, Arizona, New Mexico, Texas, and maybe a little bit of Oklahoma.  We’re planning to see the Very Large Array, visit Truth or Consequences, and check out The Black Hole in Los Alamos.  That is, if the trailer stays connected and we don’t break down too many times on the way.

I though this would be a good opportunity to dust off my APRS tracker so friends and family can watch our progress.

What is APRS?

APRS, short for Automatic Packet Reporting System, is a radio network that uses amateur radio frequencies to relay short messages.  Think of it as a precursor to twitter, developed 20+ years ago by Bob Bruinga, WB4APR.  The messages usually contain GPS coordinates, and they are relayed via radio to internet connected stations that send the data to the APRS-IS network.  Database servers, such as findU, cache the packets so that client software can access them without needing a radio or realtime access to the network.

The coolest client I have seen so far is aprs.fi, a clever mashup of APRS and Google Maps:

APRS map of San Francisco
APRS map of San Francisco

The hardware:

I made this APRS tracking box a couple years ago, so I’m a little fuzzy on the construction details, but it consists of the following parts:

  • A Trimble ACE III GPS module, originally used in a police car, $5 on eBay.
  • An external mag-mount powered antenna for the GPS that I found at HSC, also $5.
  • A Tinytrak3+ microcontroller-based APRS encoder and modem, $30
  • My old Kenwood TH-79A handheld 2 meter/144-148 MHz ham radio
  • A mag mount whip antenna for the HT, found at the electronics flea market.
  • An aluminum box, probably the most expensive part.
  • Some cables to glue all the pieces together, mostly salvaged from my junk box.

The APRS tracker acquires a GPS fix and the current GPS time.  Every so often (fully configurable), it transmits my position over the radio, where it is received by other APRS relay stations in the area.  Speed, direction, and altitude are also included with the position packet.  I connected a piezo buzzer to the TX signal so I hear a beep when the position is transmitted.  Within a few minutes, a point corresponding to the position shows up on the map at aprs.fi or in the findu database.

It’s really neat to play with, especially on long trips.  On a trip to Moab two years ago, my position was received by the APRS network even in areas with no cell coverage, which included most of Utah!

Note that to use the APRS system, you need to have an amateur radio license.  If you’ve ever been interested in amateur radio, this is a really good reason to get your license and start experimenting!