The following is an email sent out by Tim Cunningham, N8DEU, on Feb 23, 2003. It was addressed to those people on the packet list that have an interest in APRS. It should be considered an outline and standard practice for those people wanting to use and run APRS in the Middle Tennessee area. Seme of the information contained in the configs on this site are based on suggestions in this email.

From tim_cunningham@nospamming.com Sun Feb 23 14:27:50 2003
Date: Sun, 23 Feb 2003 13:55:25 -0600
To: "Sean \\The RIMBoy\\" sean@nospamming.com, packet@nospamming.com
Subject: Re: Mic-E decoding at an Igate

Hey Sean,

It was great to see you guys at the Dalton Hamfest. It was my first
trip to the Dalton fest and I did not return empty handed. That does
not happen too often. I75 after the hamfest was no fun. Especially,
for the passengers in the crushed Van.


The following stations have their Mic Encoder converter function
enabled on their Internet gateways:

KG4NRC APRSd215
KF4ERV WinAPRS215
KG4LVA APRSd215


KF4ERV uses WinAPRS v215 and it converts Mic-E packet differently than
APRSd. This causes a packet to be duplicated on the APRS-IS output.

One of the problems is the Mic-E conversion process creates issues with
a mobile station using the Mic-E format. This could be a Kenwood D7A or
D700, MIM module, TinyTrak, or any other device that transmits data in
the Mic-E compressed data format. This format was implemented to reduce
that amount of data on the network. Since almost every APRS software
packages convert the data locally for viewing, there is no need for an
IGate to distort the data by uncompressing it and placing it back on the
network beyond its original structure. Not only does this decrease the
bandwidth, but it adds to positional movement of a mobile station since
the converted coordinates may be rounded. This can make a stationary
mobile appear to be moving when they are parked. I have seen this
numerous times where a parked mobile moves back and forth across a
parking lot when it is parked.

The packet examples below show that some stations have their Mic-E
conversion process active on their IGates. These are for reference
examples to demonstrate the problem and not intended to embarrass anybody.
In fact, I am sure most do not even know their Mic-E conversion is
enabled or what it does to the network.



Here is an example of a station using a Kenwood D700 that transmits a
Mic-E packet:

W4OZK-1>ST4X1X,RELAY,WIDE2-2,qAo,N8DEU-4:'rEnl zk/]"6r}
W4OZK-1>APD215,WB0NOO-1*,WIDE2-2,qAS,KG4NRC:=3448.18N/08641.82Wk094/000/Mic-E/M1/Enroute... ]"6r}
W4OZK-1>APK101,WB0NOO-1,WIDE2*,qAS,KF4ERV:@151838z3448.16N/08641.81Wk094/000/Mic-E/M1/Enroute>

It is first captured by the N8DEU-4 IGate that does not converts the
packet before placing it on the APRS-IS. Moments later, the IGate at
KG4NRC captures the packet on APRSd215, converts it to a verbose packet,
and sends it back out to the APRS-IS. The APRS-IS duplicate filter could
not validate this as a duplicate packet since it was change and, therefore,
the data was sent out the pipe on the APRS-IS as a new packet. Then the
IGate at KF4ERV captures the packet and does the same conversion process
as KG4NRC. However, KF4ERV is using WinAPRS v215 and it converts the Mic-E
packet a little different than KG4NRC who using APRSd215. The APRS-IS does
not catch this as a duplicate because the packet appears to be a new one
since it is different that what the other 2 IGates posted on the APRS-IS.


Here is another example very similar to the one above.

W4GPS-1>S4TT1U,RELAY,WIDE2-2,qAo,N8DEU-4:'rC>l +j/]"6+}Send reports to pb@w4gps.com
W4GPS-1>APD215,WB0NOO-1*,WIDE2-2,qAS,KG4LVA:=3444.15N/08639.34Wj015/000/Mic-E/M2/In Service ]"6+}Send reports to pb@w4gps.com
W4GPS-1>APK101,WB0NOO-1,WIDE2*,qAS,KF4ERV:@152059z3444.15N/08639.33Wj015/000/Mic-E/M2/In Service>l +j/]"6+}Send reports to
pb@w4gps.com

In this case KG4LVA is another IGate running APRSd215 that enters the
equation. The reason you do not see KG4NRC is because the APRS-IS probably
stripped it out of the pipe as it would have looked exactly like the one
sent from KG4NRC. Since KG4LVA beat that one into the pipe, the
duplicate from KG4NRC would be stripped from the output because it was
labeled as a duplicate.




73's de Tim - N8DEU