APRS OPERATOR-PRESENT BIT 17 Sept 2007 --------------------------------------------------------------- Due to too many lights-out-nobody-home stations on the air, APRS has a bit in the APRS position packet that indicates if a live human operator is present. This was added around 2002 or so in APRS addendum 1.2. Here is how it was implemented in APRSdos for example. If the PC detects any activity at the keyboard or mouse, then the Operator present bit is flipped, a station posit is sent, and the usual decay algorithm is reset to 10 minutes for the next posit. Thus, operator presence is immediately updated. When no additional operator actions are detected, then the operator bit is canceled and the normal doubling of the decay rate resumes. Within a half hour, it is back to the minimum 30 minute rate. EXAMPLE: In APRSdos, Operator Present stations are indicated on the map with bright white SYMBOLS and all non-operator present or non-message capable symbols are shown in gray or the other 8 attribute colors depending on their other attributes (moving, fixed, dead rekoned, decayed, old, object, etc)... This bit was initially chosen as the case of the N/S byte in the Latitude. If the N/S character was UPPERCASE, then there is an operator present. If it is lower case, then no operator is present. This was backward compatible with all software for attended stations, since attended stations would all show normally. UIVIEW INCOMPATIBILITY: The problem is, that the UIview author is a silent key and so the UIview software is stagnant. Turns out, that UIview is one of the only clients that would ignore the lower case "n/s" byte. Thus, unattended stations would disappear from UIview maps. NEW OPERATOR OVERLAY CHARACTER: In response, the N/S bit has been abandoned and in its place, the use of the "O" overlay character is now proposed as the Operator Present bit in any APRS position report. ALthough most client software will not immediately display the "O" overlay, at least they will receive the original symbol without any problem. Later then, new clients can implement the switching of this bit and also the selection and display of the status of this bit. Kenwood, in the new D710 radio, has already implemented the display of the Overlay on ANY symbol, so HOUSE Icons using this bit should show up well. IMPLEMENTATION: Here are the receommended operating details of this Operator Present Feature: 1) If user activity is deteced by the keyboard or mouse, and this feature is enabled, then the OPERATOR-PRESENT BIT is set. 2) If no activity has been detected in over 30 minutes, then the bit is cleard back to not-present. ACTION: If the OPERATOR PRESENT BIT transitions from off-to-ON, then the present OVERLAY character is saved, and it is replaced with an "O" and a position packet is sent immediately. The timing schedule or decay for the next such beacon is set to 10 minutes. If the OPERATOR PRESENT BIT transitions from ON-to-OFF, then the "O" overlay is replaced with the previously saved OVERLAY character. The position timing is allowed to decay back to the normal 30 minutes default for fixed stations. DISPLAY OPTIONS: The prsence of an Operator at a station can be displayed in a special way so that it is obvious that an operator is present. In APRSdos, these station symbols are displayed in bright white. Stations that do not have operators present or are not message capable are displayed in light gray. Other clients can find other ways of display. I recommend a small surrounding color around the symbol. See http://www.ew.usna.edu/~bruninga/aprs/ symbols.html FILTERING/SELECTION: A good use of this bit is for eliminating map clutter. THe client software should have a button for "Display ONLY ACTIVE stations". The only packets that should remain on the map are: 1) Operator Present stations ("O" overlays") 2) Mobiles in motion 3) All Mic-E's that are message capable (Kenwoods). This allows for quickly checking the status of your human operators in an APRS on-air-event. Bob, WB4APR