Some ideas for antennas for AMSAT’s next generation of satellites ____________ describing some unfinished work in progre

1. Some ideas for antennas for AMSAT’s next generation of satellites____________describing some unfinished work in progress Tom Clark, K3IO mailto: K3IO@verizon.net DC AMSAT Group March 15, 2008

2. Premise #1: All the future satellites will concentrate on microwave frequencies  means Earth-to-Space (uplink) direction only  means Space-to-Earth (downlink) direction only * the 9 cm satellite band is only available in regions 2 & 3

3. Premise #2: You will need antennas about 1 Meter in diameter

4. Premise #3: The way we point antennas now is inadequate for these needs! • Present-day rotors rely on 50 year-old technology. • Rotors with sloppy gears, designed for big yagis • Potentiometers for positioning are unreliable and produce erratic results. • The typical Yaesu rotors equipped for two-axis pointing are expensive. • Computer control is an afterthought (although Howard, G6LVB’s new tracker is elegant). • Whatever you do for azimuth has to be duplicated for the elevation axis.

5. A digression . . . . • One of my colleagues, Dr Alan Rogers at the Haystack Observatory has been developing low-cost, easily reproducable student-level Radio Astronomy projects. • He has produced copious notes on all aspects of the SRT (Student Radio Telescope) project available at http://www.haystack.mit.edu/edu/index.html • The original SRT activities concentrated on 8-10’ TVRO dishes used (mostly) at 1.4 GHz (21 cm)

6. More about SRT activities #1 The following is extracted from http://www.haystack.mit.edu/edu/undergrad/srt/index.html

7. The VSRT Alan’s latest effort is called the VSRT (Very Small Radio Telescope). The VSRT makes use of low-cost 60cm Ku-band satellite dishes. Alan has made an incredible set of documentation available at http://www.haystack.mit.edu/edu/undergrad/VSRT/VSRT_Memos/memoindex.html

8. Some VSRT Documentation – one of the parts lists

9. On a trip to Haystack last year, I saw this setup bolted to a picnic table For details see http://www.haystack.mit.edu/edu/undergrad/VSRT/VSRT_Memos/009.pdf

10. So here’s the deal • The positioners Alan found are off the shelf, low-cost TVRO positioners that are designed to mount dishes up to ~1M in size. • These positioners derive their power and control from the same coax cable that provides power for the LNB and brings back IF signals in the 500-1500 MHz range, typical of ~12 GHz Ku-band TV satellites (like DirecTV). • The rotors are normally used for hour-angle control of a (nearly) equatorial antenna pointing at the Clarke Belt. They have ± 90° angle coverage and are capable of pointing to ~1° accuracy

11. More about DiSEqC • Rotor control is thru a well-established protocol that was originated by EutelSAT called DiSEqC (Digital Satellite Equipment Control). The DiSEqC protocol is defined on the Eutelsat web site at http://www.eutelsat.com/satellites/4_5_5.html • The protocol involves adding 22 kHz tones with bi-directional positioning data to the +13-18 VDC power on the coax. The rotor “steals” power when it moves. • A microprocessor in the rotor counts pulses from the motor to measure its position.

12. DiSEqC Positioners • Alan recommended Sadoun in Ohio as a source for the SG2100 rotors he is using. Sadoun had a booth inside Dayton and a large tent outside. Their website with “HH” (Horizon-to-horizon) rotors is http://www.sadoun.com/Sat/Order/Motors/HH-Motors.htm • Sadoun’s price for the SG2100 is $65. They show a new, higher performance DG280 for $90 • I located the “Eagle Aspen” DiSEqC azimuth rotor with a full 540° azimuth coverage. The ROTOR100 costs $65 from Solid Signal at http://www.solidsignal.com/prod_display.asp?PROD=ROTR100 • The ROTOR100 comes with a control box & IR Remote. Solid Signal also has the SG2100 and similar “HH” Rotors.

13. Computer Control of DiSEqC • In order to track the sun, Alan built a simple “button pusher” controller for his solar telescope. • I have started work on a low-cost controller based on the Parallax Basic Stamp. • Because computers no longer have serial ports, I plan to use USB. Parallax offers their “MOBO” motherboard with a BS2pe CPU for $70 that seems like a perfect fit. • 2 sockets for external custom interfaces. • 2 little ATMEL co-processors onboard • Stamp includes “SOUND” command with programmable frequency and duration is perfect for generating DiSEqC commands.

14. Computer Control of DiSEqC • I envision a single Stamp controlling up to 4 rotors. • Host computer will send commands like • A=327 E=42 for Az/El applications, or • H=+32 D=-9 for HA/Dec (astronomy) uses, or • B=W3VD to point at the W3VD beacon, or • ??? • Software also need to communicate in existing rotor protocols (like G6LVB does)

15. Finally • I’m planning a simple Radio Telescope project, similar to Alan’s. One interesting program would be for the amateurs to establish a web-based, world-wide 12 GHz solar flux monitor. • I’m eager to hear from others wanting to work on this concept. AMSAT will need for it to be developed and available by the time of the P3-E launch. 73 de Tom, K3IO mailto: K3IO@verizon.net