[aprssig] APRS Authors - New Symbols
HamLists at ametx.com
Thu Feb 14 10:42:45 CST 2008
> -----Original Message-----
> From: Robert Bruninga
> Posted At: Thursday, February 14, 2008 9:42 AM
> Subject: RE: [aprssig] APRS Authors - New Symbols
> Ah thanks. Do you have a special symbol for Dstar mobiles?
A good question with a simple answer: No.
Now the explanation: D-PRS is the act of converting Icom GPS information into APRS TNC2 format, it is not a protocol. Also, this is not a one-for-one (APRS<->Icom GPS) function. Basically, Icom designed the GPS function (not a part of the D-STAR specification) to simply display the position of the transmitting station without any other information. Because the low speed data sub-channel of the digital voice stream does not have error correction or detection, I instituted a mandatory checksum in the fixed message string for a station to be gated to APRS via D-PRS conversion. Because that check sum is mandatory, I also instituted a mandatory GPS symbol string (the xyz of the GPSxyz destination call in APRS) so people can chose from any of the APRS symbols with any overlays. You can see this in action at http://www.aprs-is.net/dprscalc.htm
Icom introduced GPS-A mode with the IC-2820 last year. This uses a CRC prefix on a standard APRS TNC2 format position string. This still allows selection of the symbol from the APRS tables. The D-PRS IGates (javAPRSSrvr-based software or µSmartDigi(tm) D-Gate) support both formats on the D-STAR voice channel.
Long explanation, but hopefully helps others understand the difference between Icom GPS on D-STAR, D-PRS, and APRS. I also published a detailed paper on D-PRS for DCC last year. Also, for the benefit of the people on this SIG that are not familiar with D-STAR and what we are talking about, a very quick overview: D-STAR is a specification of an over-the-air digital protocol for voice, and for high speed (128k) data. The two protocols are not compatible but carry much of the same header information. The digital voice protocol provides for a little less than 1200 bps of data to be carried with the voice. This data sub-channel is what Icom thought would be good to use for sending GPS information and what we use to convert from the Icom GPS format to APRS TNC2 format (D-PRS). Very important: the digital voice mode is NOT a digital data mode. It is a voice mode that can carry a small amount of data with the voice.
We are also using the gateway symbol (\&) with a D overlay to designate D-PRS IGates.
As you have already noted in your ToCall page, APDPRS is used to designate D-PRS converted GPS information (non-GPS-A mode). Note that GPS-A mode packets are passed as is so they can use the APIxxx destination call.
Finally, we use DSTAR* in the path to indicate the packet originated on D-STAR, not APRS-IS or on AX.25 RF.
Hope this helps.
Pete Loveall AE5PL
pete at ae5pl dot net
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