Sunday, August 26, 2012

Robust Packet Radio

A couple of days ago Chris, HB9DDF sent me an email asking how to configure APRSIS32 to work with the SCS Tracker / DSP TNC. Digging through my configuration files to get the information he needed I thought: why not put the 30m APRS gateway back online? It had been off since I went into hospital last year and the K2 and magnetic loop were hardly ever used.
SCS Tracker DSP TNC and Elecraft K2 at G4ILO
I don't know if propagation is lousy or whether things have changed since I was last on HF APRS but there seemed to be a lot less activity on the 30m APRS frequency today. An hour went by without my receiving anything. I did, however, hear quite often the "whooshing" sound of Robust Packet Radio (RPR) stations a few hundred Hz down. So I decided to configure the TNC to work in RPR mode.

Robust Packet is a mode obtainable in 300baud and 600baud versions that has been designed to take advantage of the capabilities of digital signal processing (DSP) in order to obtain reliable communication over a normal less than perfect HF path. To anyone who has experience only of traditional 300baud FSK packet RPR has too be seen to be believed. Packet after packet was decoded and displayed by APRSIS32 while conventional packet transmissions on the adjacent channel just flickered the DCD lamp and were discarded due to errors.

Robust Packet is a proprietary mode developed by SCS and is only supported by SCS TNCs. As far as I know no description exists that would enable someone to develop a PC implementation that uses a sound card. In that respect it is pretty much like Icom and D-Star. I would much rather use an open standard.
G4ILO-10 joins the Robust Packet Network
But RPR works where the old-fangled 300baud FSK invented to work on the analogue modems of 30 years ago doesn't. I think it is in keeping with the spirit of ham radio to use state of the art technology where it provides clear benefits to communication.

So G4ILO is now part of the Robust Packet Network.

4 comments:

John Zaruba Jr said...

Hi Julian,

I hope your feeling as well as you can.

A minor point, D-STAR is an open standard that was developed by the JARL. Certainly, Icom is the only major commercial manufacturer but there is a thriving "cottage industry" of D-STAR compatible devices like iNet Labs, Nortwest Radio, and Dutch*Star. There are several hams that have built non-Icom repeaters and there are several D-STAR "hotspot" kits available for building your own infrastructure where none is extant.

73,

John K2ZA

Julian Moss said...

Hello John. I'm feeling quite well now, if not as fit as I was.

D-Star is an open standard, but it uses a voice codec that is proprietary making the development of a free alternative that is compatible with the Icom systems impractical if not impossible.

Similarly, APRS is an open standard, as is AX25 packet networking. You can use alternative data modes to FSK300 such as PSK63 or GMSK amd people have done so, just as others have developed a free voice codec, but SCS patents prohibit the development of a free data mode compatible with RPR300.

SCS Robust Packet in my example, and the AMBE voice codec in yours, are both proprietary products running over an open network. I think the parallels are very close.

Julian, G4ILO

Mads said...

Hello Julian

I'm happy to hear you are feeling quite well!

I was looking at the your photo and noticed that your map looks considerably different from mine. What tile set are you using?

73! Mads, la1tpa

Julian Moss said...

Hello Mads. I'm using the Mapquest tile set.

Julian, G4ILO