APRS on Google Maps

I ran across an interesting utility the other day. It allows the overlaying of APRS data on top of Google Earth. The utility is called APRSKML, and can be found here. The utility is well documented, and I was able to set it up within minutes. If you’re in the south central BC area, try the following settings (on the APRS IS screen):

  • APRS IS Server: va7ylw.ocarc.ca:14580
  • “Reconnect on Restart” checked
  • “Confirm Reconnect on Restart” unchecked
  • Filter: r/49/-119/300

Set your callsign and APRSIS auth code as appropriate. The magic comes in to the filter line (make sure you put something in here – leaving it out will swamp the software with too many stations, and it will eventually crash). The three numbers correspond to lattitude, longitude, and radius.

Kenwood TM-D700A Repair

A fellow ham approached me with a defective Kenwood TM-D700A transciever. The unit showed no signs of life. There was no display, and no response to pressing the power button. The only hint was that the cable between the radio and remote head had recently been repaired.

Luckily, I have the service manual for this radio. It was essential in this repair. After checking the obvious (making sure that power was getting to the radio), I decided to check that power was getting to the remote head. In order for the soft power switch to operate, there is a constant supply to the remote head. There should be 9.66v between pins 1 and 4 of the remote head cable. In this instance, there was no voltage at all. A simple power supply around D903, Q910, Q911 and Q913 creates the 9.66v signal from the raw 13.8v. Again, no voltage at all. The supply is protected by fuse F902. This is a 1.8A tiny surface mount fuse. Without the schematic, I probably wouldn’t have found it. It’s located just below the voice synthesizer connector (see rather bad camera phone picture). I was unable to locate such a tiny surface mount fuse, so I replaced it with a 2A picofuse. I carefully bent the picofuse leads to attach to the original solder pads. A small dab of glue gun glue held the fuse up off of the circuit board to avoid any shorts.

After re-assembling the radio, all functionality checked out. I suspect that the original damage to the head cable caused a short which blew this fuse.



It’s time once again for the CQ WW WPX ham radio contest. I like to participate in contests just to get a few more callsigns in my logbook. However, this time, I’m not sure I’m going to get much chance. We’re picking up a new puppy tonight, and I think spare time is going to be a rare commodity over the next little while. I’ll have to squeeze a few contacts in just so I can say I participated. I’ll post some puppy pictures in my moblog tonight.

Adding Additional Analog Inputs on a Kantronics TNC

I just posted a how-to article describing adding additional analog inputs to a Kantronics TNC. Out ham radio club was installing a new APRS repeater, and had asked if there was any way of monitoring multiple analog values (specifically, two battery banks, the presence or absence of AC mains, and a temperature reading). I spent some time studying the schematics and doing some research on the web. I was unable to find any specific how-to articles other than vague references to using additional CPU pins. After building and testing the circuit, I decided to post an article describing the process for anyone interested in doing the same thing.

Field Day

What a busy couple of days. Last Saturday/Sunday was amater radio’s annual Field Day event. This is a 24 hour event that involves lugging thousands of dollars worth of radio equipment out into the middle of nowhere, and proceed to chant the same incantation (“CQ Field Day, CQ Field Day”) into the microphone for 24 hours, only to gather up all of the equipment and take it home again. The weekend consists of junk food and mosquitoes.

Actually, it’s lots of fun. It’s basically an emergency preparedness exercise, with a big social element thrown in. This year, we were located in Mission Creek Park in Kelowna, BC. This gave us great public exposure, with lots of people asking us questions.

This year was a double-whammy, because right after Field Day was the annual Canada Day contest. This time, we were holed up in our club shack, but the incantation was similar (“CQ Canada Day, CQ Canada Day”). I must admit that this year I sneaked away from the Canada Day contest to grab some decent shut-eye in my own bed.

Now it’s time for me to get back to work…