APRS Mic-E settings?

[BJ_NORTON]

I use a kenwood d710 and most of the time I operate APRS on one band and talk on the other. I have the status text set to show what frequency I am using on the voice side of the radio.

Today I was driving along chatting to a friend in another city when another station broke in. He told us how he saw me on APRS and used the auto-tune feature on his radio to quickly find us. he was surprised to hear us talking because my Mic-E setting showed me as off-duty.

I thought the Mic-E was intended to be used to encode your postition when you used the PTT and that some repeaters were setup to either re-transmit your position on the national APRS frequency, or act as an iGate and route it to the internet. Also I was under the impression that the only people who really paid attention to that were groups that were involved in some special event (SAR, or marathon support...). Am I mistaken? should I pay more attention to the Mic-E status? Is there any sort of official guidance like there are for suffixes?

 

[LtDoc]

Those 'status' remarks are very 'general' and have no particular 'set' meanings. They can be interpreted to mean anything you want them to mean, within reason. As in, when is a ham 'on duty', or 'off duty'? The only one to not use unless it's a fact is the "Emergency" status thingy. I think there are several people who should be using the 'committed' status!
So, are you doing something wrong? Nope, not really.
- 'Doc

(PS - I use 'special'. That's because i am special (to me), my car is special (to me), and it looks like that little bus...)

 

[AK9R]

I thought the Mic-E was intended to be used to encode your postition when you used the PTT...

That was the original intent of Mic-E, but the APRS world has changed quite a bit since then.

Mic-E is a method of encoding an APRS position report that was designed to make the packets very short so they could be reliably sent at the beginning or end of a voice transmission like MDC data in the commercial radio world. In Mic-E, the latitude along with some other data is encoded into the Destination Address field (7 bytes) of the AX.25 UI frame and the longitude along with some more data is encoded into the Information field (as short as 9 bytes) of the UI frame. This encoding uses all of the printable 7-bit ASCII characters instead of just 0-9, A-Z, and a-z. This made the packets much shorter than the "long-form" position reports using clear text that was common in APRS at the time.

The Mic-E specification includes a 3-bit message identifier that is encoded into the first three bits of the Destination Address field along with the latitude. The standard message identifiers are M0 (Off Duty) to M6 (Priority), C0 (Custom 0) to C6 (Custom 6), and Emergency. The intent was that a group might agree to the meaning of the six custom message types and use them as they saw fit.

For whatever reason, Kenwood chose to use Mic-E encoding when they developed their first APRS radio, the TH-D7 handheld. They have stuck with Mic-E in their subsequent APRS radios and Yaesu is using Mic-E in their APRS radios, too.

As indicated, not many people really pay attention to the Mic-E message types, though, obviously, someone does hence the question the OP received. If you had several people working an event and they all had APRS Mic-E encoders, then you could use Mic-E to convey quite a bit of information without spending a lot of air time to convey the same information using voice. In general practice, though, I'm not sure Mic-E messages are that important.

You can read about Mic-E encoding in Section 10 of the APRS spec at:

http://www.aprs.org/doc/APRS101.PDF