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On 9/21/2011 9:32 AM, Joseph M. Durnal wrote:
<blockquote
cite="mid:CAAbqqEO3AYouGa7z1kojCvabssTzHNEGGfvSW4OzhpYS9pvp2g@mail.gmail.com"
type="cite">
<pre wrap="">I need to think about the mic-e packet. Obviously, if one takes their
TNC and watches the 144.39 data go by on the terminal, they'll see a
lot of mic-e. I'm still working on how far into the weeds I should
go. I could keep it simple and just say that the destination address
contains the encoded latitude, NS/EW, & message and the info field
contains the encoded longitude, course speed, & symbol. I don't think
most of my audience will find much more than that very useful.
</pre>
</blockquote>
<br>
The things significant about Mic-E:<br>
<br>
<br>
1) The MIc-E format and hardware was originally created to
create an extremely short position and ID burst (about 1/3rd to 1/2
second) at the end of VOICE transmissions when the radio's mic was
unkeyed on a voice channel. Hence the name MIc-E (short for "Mic
Encoder"). <br>
<br>
The intent is for a TNC to be attached to the receiver side of a
voice repeater. The TNC detects the tail-gate Mic-E bursts on voice
transmissions, and retransmits them on the 144.39 APRS-only channel
from an additional transmitter at the repeater site. The TNC's
"carrier detect" is used to mute the retransmission of the packet
burst on the repeater's voice output channel. <br>
<br>
<br>
<br>
2) Mic-E is a highly-compressed format that is less than
ONE-THIRD the length of a normal APRS packet, and ONE-TENTH the
length of transmitting a raw NMEA position data string taken
directly from a GPS. The Mic-E format is valuable, even on a
non-voice data-only channel. The shorter packet takes less air
time to send, increasing the number of transmissions per minute
possible on the RF channel. Less obviously, it significantly
increases the reliability of those transmissions because the
much-shorter packet is less likely to collide with other stations,
or be corrupted by mobile flutter or pops of noise.<br>
<br>
<br>
<br>
3) Mic-E format crams the latitude value into what is normally
the "destination address" that usually begins "APxxxx". The
apparent "destination callsign" of a Mic-E station, as monitored on
a TNC's output, will actually change as the north/south position of
a mobile changes. <br>
<br>
<br>
<br>
4) Additionally, part of the Mic-E compression is achieved by
placing TWO binary-coded-decimal digits of the latitude and
longitude values in each 8-bit byte of data, instead of a single
ASCII character in each byte. As a result, Mic-E-formatted data
is not human-readable like conventional APRS posits when viewed
directly out of a TNC. (You see a seemingly random "gibberish" mix
of letters, numbers and punctuation marks.) However, all APRS
software, hardware (like Kenwood and Yaesu radios), and APRS
websites (like findu.com and APRS.fi) know how to decode this
"alphabet soup" correctly. <br>
<br>
<br>
<br>
5) The term "MIc-E" actually refers to several different
things: <br>
<br>
o A hardware device (the TAPR "Mic-Encoder") created
decades ago, and long since discontinued. It was a box somewhat
similar to a TinyTrack, that inserted inline between the radio and
it's microphone, to generate these bursts each time you unkeyed on a
voice transmission. (Today's Tiny Tracks can still monitor the
PTT line, and burst-on-unkey on voice if desired, as can the Kenwood
and Yaesu APRS radios.)<br>
<br>
o The short-form data format involving
data-in-the-destination-field this device used, that is still used
today by all Kenwood and Yaesu radios, and optionally by TinyTracks.
<br>
<br>
o The compression algorithm that these packets use; i.e.
"That was a Mic-E encoded packet."<br>
<br>
o A voice repeater equipped with this feature; i.e. "WR8XYZ
is a Mic-E repeater".<br>
<br>
<br>
<br>
<br>
<br>
<hr size="2" width="100%"><br>
--<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
=== Now relocated from Pasadena, CA back to 8-land (East Lansing,
MI) ===<br>
Skype: WA8LMF<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a><br>
<br>
===== Vista & Win7 Install Issues for UI-View and Precision
Mapping =====<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7">http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7</a><br>
<br>
*** HF APRS over PSK63 ***<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/APRS_PSK63/index.htm">http://wa8lmf.net/APRS_PSK63/index.htm</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a> <br>
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