Here are some frequently asked questions about the APRS tracking program at mail2600.com and APRS in general.
Questions
Answers
Probably not. Most certainly not!
The most likely explanation is some sort of system failure. In approximate order of likelihood:
- The aircraft is not in an area of radio coverage. This
happens when the airplane is too low to reach the nearest ground
station or is otherwise blocked by terrain.
- The mail2600.com server is (temporarily) down or the feed to it
of position reports from the ground stations has been (temporarily)
interrupted. Here's an alternate server
but it is not always up to date and it may be discontinued at some
point in the future (so don't use it as a matter of routine).
- The pilot has turned off APRS tracking either on purpose (e.g. to
use the tracker radio for voice communications) or accidentally (e.g.
bumped a switch).
The aircraft position and other
parameters (as measured by an onboard GPS) are transmitted from the
aircraft in real time to a network of amateur radio (ham) ground
stations on VHF. The ground station(s) receiving the transmission
forward it to a network of servers which feed it to this site's
server.
The feed is parsed and the resultant
parameters are used to populate a database (also on this site).
The database is queried and displayed by scripts on this web site. Other web sites (see the
APRS Tracking Links on the sidebar at the left) also receive the same feed but populate and display their own databases.
The on-board equipment needed for tracking can cost from about $75 to over $400 and consists of the following:
- GPS (often the aircraft GPS can be used instead of a dedicated one).
- Transceiver. An amateur radio transceiver capable of transmitting on 143.390 MHz at any power level.
- Antenna, An external antenna is best but a "rubber dummy load" can give acceptable results.
- TNC or modem-like device that converts the digital data from the
GPS to audio tones transmitted by the transceiver. One low cost
device is the Byonics TinyTrak3.
- Alternately, a transceiver like the Kenwood TH-D7A handheld or TM-D700A or TM-D710A mobile radios require no TNC and are useful for voice communications on amateur frequencies. Update 19 Oct 2008: it is my understanding that these Kenwood radios are obsolete and no replacements have been released.
In order to reduce the clutter and
provide a good user experience, only APRS stations (preferably on
aircraft) with
"interesting" tracks (not just a commute or a home station
beaconing) are included here. (Yes, I know: there are some
exceptions listed in the
Current Positions of All Stations in the Database)
If you would like to have your APRS station tracked here email Joe,
K7JD: jdubner at yahoo.com. Be sure to specify the callsign-SSID or N-number
you'll be using.
APRS stations not included here can most likely be found at one of the
APRS Tracking Links on the sidebar at the left.
aprs.fi is highly recommended.
- For how long will my position reports be available?
The goal is to retain position reports indefinitely for stations with
interesting tracks
(as defined
above). In order to maintain database file size, other position reports will be deleted
periodically. There is no set schedule for deletion but don't expect position reports to be
kept more than two weeks or a month unless they associated with an aircraft.
Update 19 Oct 2008: The size of the position report database has grown at an alarming rate and the
Current Position of All Stations
page has taken on a cluttered appearance. This is due to a combination
of reasons but you can do your part by not continuously beaconing if
you are in a fixed location (this produces a very "uninteresting track")
and using restraint in setting your in-motion beacon rate (not more
than once per minute recommended). In addition, use
SmartBeaconing if it is available for your tracker.
The following steps are
being taken to keep the site streamlined and simple to use for tracking the
active aircraft APRS stations for which it was designed. (For general
purpose fixed-location APRS stations,
aprs.fi or (good luck!)
findu.com are recommended).
- Position reports for almost all stations will be purged from the database after 30 days.
- In addition, stations that have no activity for some
(unspecified) long period of time will no longer be tracked even if
they generate new position reports. If you are concerned that
your station has been permanently deleted from this site due to inactivity, email Joe,
K7JD: jdubner at yahoo.com specifying the callsign-SSID or N-number of
interest.
- Finally (and this has been true for some time), position reports are discarded if they are exact duplicates of recent ones.
- How do I use Google Earth to "fly along" or play a tour of a track?
Lets assume you're reading this because you'd like to try the Google Earth network link or
track/tour functionality from the
user interface page
(
items 7. or
8.) or the page
that displays
all tracks for a particular station.
Lets further assume that you have
Google Earth installed
on your PC and have at least a little bit of experience using it.
The Google Earth
network link functionality is only useful if a station is presently
in motion.
It displays a "birds-eye view" of what the pilot sees and is refreshed every 30 seconds.
If the aircraft has moved the station's icon "flys" to the new position and the map is refreshed.
No operator action is necessary to see a continually updating display. When the station stops moving,
there are no further updates.
The Google Earth
track/tour functionality displays a previously completed track or
"replays" a track by "flying" a tour of it. It creates a collection of points in Google Earth's
Places pane (under
Temporary Places) that can be viewed or "toured".
Select
Tools | Play Tour from the menu or use the controls below the
Places
pane to start, pause, or stop the tour.
Here are some tips for optimum use:
-
Do not check more than one network link or track simultaneously in the Places pane or
Google Earth will attempt to fly back-and-forth between them.
This is probably not the effect you want.
-
You can save an interesting network link or track permanently under My Places and revisit
it by checking it whenever you run Google Earth.
Again, check only one item at a time.
-
The default parameters are generally satisfactory for the Tour but they can be modified to
taste by selecting Tools | Options | Touring tab from the menu.
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