Upgrades on Friday or Saturday

I'm planning to upgrade aprs.fi on either Friday evening (30 Oct 2009 around 1500z) or Saturday morning (31 Oct 2009 around 0700z). I'll be reconfiguring the service to use a completely different web server software than before, so there will be an outage of some sort. If everything goes well, it won't be more than a few minutes. There might be some surprises on the way, since I don't have a proper lab setup to run the new configuration with a simulated heavy load.

Beta test: Multiple target tracking on live map

I've done some rather heavy changes in the map code, which might well break some things. The big visible change is that you can now look up and track multiple targets (up to 20) in the real-time map. I'm mostly worried that it'll slow down things too much, but we'll see...

To try it out, surf to the beta site and enter a comma-separated list of callsigns (OH7LZB-9,OH2RDK,OH2RDS), or click 'start tracking' on multiple targets!

It's also running with a completely different web server software than before. We are still fixing bugs with the new setup, so the beta service might be unavailable at times. Please report any bugs as comments on this post, or send a private email to the address shown on the profile page.

Thank you!

- Hessu and the bug-eating cats

Multiple targets on static maps

The static map page can now display up to 20 targets at the same time! Just enter the calls, separated by a comma. It works with wildcards, too, letting you select multiple matches simultaneously. For example:

RAUTAUOMA, OH2RDK, oh2rd*

The exact matches (rautauoma and oh2rdk) are preselected, and the wildcard matches are not.

Implementing this on the live map will be slightly more complicated, but unavoidable. :)

PS. Got my OT2 running with my Garmin Nüvi 350 today. Details will be posted later. It's very cool indeed.

Password recovery fixed

Oops, forgot to mention yesterday that the password recovery functionality was broken since Thursday, and was fixed in yesterday's update.

Repeater antenna installation day

For a change the photos in this blog post are not completely off-topic - we were installing new antennas on the OH2RCH repeater and igate site on Saturday. The operation was very well planned, all the required bits and pieces were there, the weather was excellent, and the execution was professional (like the components).

An FM broadcast antenna, which was used as the 145 MHz repeater transmitter antenna (together with a circulator and dummy load to handle the SWR), was removed and replaced with a proper 2-element stacked dipole for 145 MHz. Also, a 432 MHz repeater antenna with 4 stacked dipoles for RX and 2 dipoles for TX was added. And an extra 145 MHz dipole on the side of the mast. The 145 MHz RX antennas on the top of the mast, which are shared by the 2M repeater and the APRS igate, were not touched at this time. The new single dipole could be used for a transmitting igate to support 2-way messaging. There's another igate handling that in the area already, though.

The work happened at 70 meters above ground level, right above the second guy wire attachment point. Here is Antti, OH2MNI, attaching the 145 MHz dipole pair to the mast:



And here you can see yours truly, holding the braking rope which keeps the 2M antenna far from the mast while the antenna is being pulled up, so that it doesn't break all those microwave link antennas on the way up. On my right side is one of the guy "wires" - there are 6 of these on three sides of the mast, a total of 18.

And here, on the left side of the mast, are the completed antennas. On the top right side of the mast is a fancy new wind turbine, which is generating 48V DC to help power the commercial network equipment on the site. Green energy, global warming, you know the story. It was installed this summer, and it's already broken - the bearings are making so much noise that the neighbors are more than slightly annoyed.

Thanks go to: OH2LAK (the brains of the operation), OH2FDA, OH3GMZ, OH2MNI, OH2GLG, OH3GMZ and Markku V (the mast pro). More photos by OH2LAK and OH2MNI...

New bad GPS fix detector algorithm installed

I've just installed my new bad GPS fix detection algorithm. It should detect bad fixes about as well as before, but produce less false positives. The new algorithm looks at the previously received packets instead of the previously accepted packets, and is also slightly adaptive, taking into account more history than just the previous single accepted position.

It should work better for jets (traveling close to 1000 km/h), although during the takeoff acceleration some points might be dropped. After some initial test flights we'll be fixing that. :)

It should also better handle the case where the initial transmission happens to be somewhere far off. It seems like there are a bunch of stations which always wake up in Tokyo and then start transmitting their correct position in the US or Europe. Probably the GPS manufacturer has decided to show it's office location instead of the standard 0/0 lat/lon, and either does not indicate the bad fix in the NMEA sentence, or the tracker ignores that bit of information and transmits the bad position. These should now jump to the correct position after just a couple of packets.

The algorithm also ignores positions which were sent more than 2 hours ago, so if you take an intercontinental flight and start transmitting your new position immediately, it should just work!

Feedback is more than welcome!

Status and comment texts

As a little early morning exercise I've made aprs.fi show the status message in the info balloon of the current position on the real-time map, and also in the KML. Status message is shown in purple, and the comment text is shown in green.

There has been some confusion about these messages. There are three kinds of "status/comment" messages you can attach to your position. For example, SM4IVE-9 (info) is sending two of them.

The comment text is sent together with the position, in the end of the position packet. Here's an example packet with a comment text of www.sm4ive.com:

SM4IVE-9>APERXQ,WIDE2-2,qAR,SM5NRK-2:!5908.38N/01532.45E>000/000/A=000148www.sm4ive.com

The status message is sent as a separate packet which starts with a '>' character:

SM4IVE-9>APERXQ,WIDE2-2,qAR,LA6TMA-1:>{AT0B4}aprstracker-0.11-16f648

The Mic-E status message is encoded in a mic-e packet using just a few bits, and can contain one of these 8 standard messages: Off duty, En route, In service, Returning, Committed, Special, Priority, Emergency. 7 custom messages (Custom 0 to Custom 6) are also defined. All Mic-E packets contain this status message, and it only consumes a couple of bits in the message, so this requires the least bandwidth from the APRS channel. On the other hand, it can only express the few predefined values.

I would recommend using only the comment text, since it is sent in a single packet together with the position. The status message is sent in a separate packet which increases congestion.

If a status message is required (for example, if the text really needs to be so long that it doesn't fit in the comment text), the status message should not be sent too often. Certainly not as often as the position packet.

In the following photo Armi frowns upon seeing a long, static status packet: