Proposed APRS OPS Modes for the ECHO Satellite 18 Oct 2003 ---------------------------------------------------------------------- WB4APR ECHO will launch this year and carry a tremendous capability and flexibility for communications experiments in the Amateur Satellite Service. With multiple user receivers and 3 downlink transmitters almost any communications mode can be supported. The problem is, how to share the numerous modes and configuration possibilities so that most of the thousands of potential users are generally satisfied. Having too many conflicting modes, and complex operating schedules actually detracts from the optimum satisfaction by the general cross- section of users. This paper has no official basis with AMSAT nor the ECHO design team and is offered only as a draft-strawman to serve as a target for discussion by the AMSAT community as to how it will operate AMSAT ECHO. There are three primary recommendations: 1) AMSAT should designate an ECHO Operations Committee who will manage the day-to-day operation of the spacecraft to best serve users. 2) AMSAT should publish a clear USER SERVICE AGREEMENT that specifically defines the rules, limitations, recommendations and requirements for users to use the spacecraft. 3) The default operating mode should generally be optimized to satisfy the largest cross-section of users while balancing simplicity with complexity and easy use with experimental modes. These points will be addressed in reverse order. DEFAULT OPERATIONS MODE: ------------------------------- To minimize frequent mode changes and to provide the most users with something they can use most of the time, this paper proposes a nominal initial operating configuration. Other experiments may be conducted periodically and other modes developed as software matures, but we need to start somewhere. The basis for this approach is the consideration that for maximum utility in education, student and new operator outreach, common modes must be available on a routine basis most of the time. Therefore the following default operating mode is proposed for the 4 uplink receivers. I called this configure "WAVE" for its primary modes: MODE RX DESCRIPTION UPLINK DOWNLINK ---- --- -------------------------- ---------- ----------- W RX1 WISP Multiuser File System 145.xxx 4W 435.xxx A RX2 WISP and APRS shared 145.yyy (shared with above) V RX3 Voice FM (PL enabled) 145.zzz 8W 435.zzz E RX4 Experimental - (HF) Multiuser 29.400 S-Band WFM (LV) Lband Voice 12xx.xxx S-Band WFM (LB) Lband Bent Pipe 12xx.xxx S-Band WFM (LD) Lband digital 12xx.xxx S-Band Digital Key factors involved in this arrangement are: WISP: A continuation of the very successful file store and forward system use by all of the previous PACSATS. With two uplinks (RX1 and RX2), user contention is shared for improved uplink throughput. Distribution of files, news and bulletins will be via this system. The default baudrate is 9600 baud. This system will best serve mobile portable and remote travelers by giving them remote communications access via SATgates back to the internet. I'd rather see 9600 baud used to give solid reliability to simple users with OMNI antennas most of the time, rather than giving higher speed but then requiring tracking. APRS: APRS mode simply represents the enabling of UI digipeating of UI packets to be merged into the 9600 baud digital downlink. Enabling of UI digipeating as a shared mode with the PACSATS has a legacy that includes AO-16, UO-22 and IO-26. UI digipeating users are constrained to only uplink on Receiver RX2 to minimize contention with the WISP system. UI digipeating is fully compatible with the Kenwood TM-D700 and TH-D7 Mobile and Handheld APRS radios with only whip antennas. APRS I-gates feed all UI packets heard on the downlink into the worldwide APRS internet system. VOICE: FM Voice relay (EZ-Sat) continues the legacy of UO-14, AO-27, SUNSAT, SO-50 and others to support the most popular AMSAT mode which can be received by any user with an FM HT. Voice and SSTV may share this mode when suitable nets are scheduled to support special events. EXPERIMENTAL: Because of the very high doppler and short duration passes, the S-Band downlink will use Wideband FM compatible with any FM broadcast band receiver as the nominal mode for this transmitter. Using 75 KHz deviation, Only minor Doppler adjustment twice or so per pass is required. Nominal AO-40 S-Band receive systems feeding any FM system set to Wideband FM should work well for the downlink. Several experimental uplinks are proposed: (HF) HF (CW,SSTV,PSK-31) - The preferred default for the experimental RX4 receiver should be a 10m HF uplink which can contain dozens of simultaneous users including CW, SSTV and PSK-31. By tuning the HF receiver to 29.400, an entire 3 KHz of HF spectrum can be relayed full duplex in the wideband FM downlink. This is Identical to the HF transponder on PCSAT2. In this 3 KHz of audio, the lower 800 Hz can be multiple narrowband CW users, 800 to 2000 Hz is available for SSTV, and 2000 to 3000 Hz is dedicated to PSK-31 users. This downlink can be received, demodulated and displayed by anyone with an S-Band downconverter, a broadcast band WFM receiver and soundcard DSP software. (LV) L-BAND VOICE: The RX4 can be tuned to any L-Band uplink (preferably set to Wideband FM) for experiments. Using Wideband FM on the uplink and S-Band downlink solves the severe Doppler problem, though amateurs will have to build their own WFM exciters. (LB) L-BAND BENT-PIPE DIGITAL: Using WFM digital modulation fed to the the wideband FM S-band downlink, data rates up to 38.4 KHz or higher can be accomodated in a bent-pipe mode. (LD) L-BAND DIGITAL: Unfortunately, The S-Band transmitter shares the same data modulator as the UHF transmitters, so any use of S-Band for high on-board-originated data rates precludes any other digital modes or data rates on UHF at the same time. USER SERVICE AGREEMENT ---------------------- The concept of a User Service Agreement worked well for PCsat. After some initial consternation, most users in the Amateur Satellite Service soon realized that having a well known and published set of guidelines, recommendatoins, and rules for standard operation were in their own best interest. Having operating parameters, protocols and clearly defined operating objectives published and available in real time via a WEB page and via the live downlink bulletins gave users clear guidance how to optimize operating modes for everyone. For example the WISP channel clearly only works well if all users are using the WISP protocol which enforces unbiased sharing. Similarly, the APRS channel works best if users adhere to the standard APRS duty-cycle recommendations and power levels. These same guidelines should also apply to the Voice transponder. That is, there will be times when free-for-all QSO's are invited, but in general it has clearly been established that maximum effectiveness of a operating as a directed net. The details of recommended VOICE operating nets via LEO birds is beyond the scope of this text, but is included on http://www.ew.usna.edu/~bruninga/tbd.html ECHO OPERATIONS COMMITTEE ------------------------- AMSAT-NA president Robin Haughton and Director Rick Hambly have already begun the groundwork for establishing the Echo Operations Committee. I look forward to the operations of this body and the potential for good leadership and efficient operations planning for this new satellite. The first item should be the declaration of a mission statement which will serve as the guiding principles for operations. A possible strawman draft might be: SUGGESTED ECHO MISSION STATEMENT: The mission of ECHO will be to serve the communications needs of users worldwide in the Amateur Satellite Service in accordance with the rules and objectives of the ITU and IARU. Such usage will balance the needs for reliable routine digital and voice communications as well as experimental modes. Included in this service is the recognition of the educational and out-reach potential of this simple-to-use, but highly flexible spacecraft as well as its potential use for mobile and portable operation in remote areas and support of emergency or special event comunications needs. Respectuflly Submitted Bob Bruninga, WB4APR