[aprssig] Object Timestamps and 111111

[Tapio Sokura]

Hi,

On 12.12.2010 16:58, Lynn W. Deffenbaugh (Mr) wrote:
> Any pointers to the definition of the timestamp on object packets,
> especially the spec of the 111111 special value (which the newer
> Kenwoods appear to accept as a z, but not an h) and what it means.

Basically it means the 11th day of a month at 11:11 (am) or the time 
11:11:11 (am), depending on whether it's followed by z or h. The pdf 
spec doesn't treat it as a special value at all. I haven't gone through 
Bob's APRS addendums, they might contain something more about this.

000000 has been used by some as the invalid timestamp format as well. 
But I guess 111111 is nowadays preferred, because 111111 actually is a 
valid timestamp, for both h and z. 000000z is not valid, because there 
is no 0th day in a month. An APRS program that checks the validity of 
the timestamp might throw the whole packet away, if the timestamp is 
invalid.

The reason for using a seemingly valid, but in reality invalid 
timestamps (like 111111h) is that not all object transmitters have a 
realtime clock, and/or are not capable of transmitting packets that have 
a changing content. A typical example of this is any regular TNC, whose 
beacon text is used to transmit APRS objects. The item format would be 
better suited for transmitting timestampless "objects", but I guess the 
support for items in APRS software and devices is not as prevalent as 
object support.

   Tapio