SCAMP on-air testing commences

The Sound Card Amateur Message Protocol - or SCAMP - is not just a conference paper topic anymore.

On-the-air testing of the digital communication protocol began in late November, and the first transcontinental communication using SCAMP occurred on December 4.

SCAMP is designed to eliminate the need for pricey external hardware for passing e-mail traffic on relatively narrow-bandwidth channels. Rick Muething, KN6KB, prepared a presentation on SCAMP for the ARRL-TAPR Digital
Communications Conference in September.

"SCAMP is an example of what is now possible with sound card, computer and software technology using cooperative amateur efforts," he says. "SCAMP and similar programs like DIGTRX for image transmission offer low-cost alternatives to dedicated or proprietary hardware."

As Muething explains, SCAMP is intended for transmitting messages - text with binary attachments - via 2-kHz bandwidth HF and VHF voice channels. The program is compatible with Winlink2000. SCAMP uses the Redundant
Digital File Transfer (RDFT) transport layer, developed by Barry Sanderson, KB9VAK, with the addition of Automatic Repeat Request (ARQ) - the technique all "linked" modes use to ensure error-free transmission - and message layer protocols that Muething developed. He says SCAMP offers a moderate-throughput, error-free protocol that works using
conventional sound cards and modestly powered computers.

The RDFT utilities and documentation for the Windows and Linux operating systems have been released under the GNU General Public License (GPL).

Muething says a dozen dedicated testers began initial on-air testing on HF and VHF November 27 using the alpha version of a Windows-based SCAMP client called Paclink SCD that he and Vic Poor, W5SMM, developed.

In addition to Muething and Poor, alpha testers included Scott Thile, K4SET; Bud Thompson, N0IA; Bill Hickey, AB7AA; Howard White, VE3GFW; Dave Wagner, WA2DXQ; Lor Kutchins, W3QA; Larry Trullinger, KB0EMB; Mike Burton,
N6KZB; Bill Kearns, WB6JAR, and Steve Waterman, K4CJX. Primary testing was done on 40, 30 and 20 meters, and VHF testing was carried out on 2-meters using both FM and SSB. Alpha testing will continue over the next several weeks, and beta testing is set to crank up in February, Muething says.

The first successful transcontinental exchange of Amateur Radio e-mail messages using SCAMP took place December 4 on 20 meters between N6KZB in Temecula, California, and W3QA in West Chester, Pennsylvania. Each station ran
70 W.

"Several other two-way exchanges were also made over the weekend as operational and protocol bugs were fixed in the alpha software," Muething reports. "The throughput of SCAMP adjusts to the channel quality, reaching a current net maximum of about 4800 bytes per minute before compression gains."

Muething says SCAMP doesn't require anything more than a 1-GHz class Pentium or Celeron processor with a minimum of 128 MB of memory to reach full throughput. Lesser systems may be used at reduced throughput.

The complete SCAMP specification is available and will be released under the GPL as a blueprint for client developers to insure compatibility across different implementations. Muething says further protocol optimization continues to up system throughput and improve its robustness in poor HF multipath channels.

He'd also like to see some band plan restructuring to "open up spectrum for digital modes and encourage new experimentation and development like SCAMP." The ARRL has sought comment from the amateur community on draft proposals seeking to regulate subbands by emission bandwidth rather than by mode. At this point, the proposals remain a work in progress, and the ARRL has not petitioned the FCC for any changes.

Muething has more information on SCAMP.
Contact him via e-mail.
Information on RDFT is available on the Web.

Source: ARRL Letter - courtesy of The American Radio Relay League

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