Some ideas for antennas for AMSAT’s next generation of

satellites____________

describing some unfinished work in progress

Tom Clark, K3IOmailto: K3IO@verizon.net

DC AMSAT Group March 15, 2008

Premise #1: All the future satellites will concentrate on microwave frequencies

United States Microwave Allocations

Amateur Service in the USA Amateur-Satellite Service

Band(MHz)

Bandwidth(MHz)

Band (MHz)

Bandwidth (MHz)

23 cm: 1240-1300 60 1260-1270 10

13 cm: 2300-231013 cm: 2390-2450

1060

2400-2450

50

9 cm: 3300-3500 200 3400-3410 * 10

5 cm: 5650-5925 275 5650-5670 5830-5850

2020

3 cm: 10000-10500 500 10450-10500 50

1.3 cm: 24000-24250 250 24000-24050 50

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

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

Freq, GHz

, cm1M dish size in

Approx Gain, dBi

Beamwidth Degrees (FWHM)

Pointing Accuracy, Degrees

1.26 (L) 23.8 4.2 16.4 33.3 6.7

2.4 (S1) 12.5 8 22.0 17.5 3.5

3.4 (S2) 8.8 11 25.0 12.3 2.5

5.7 (C) 5.3 19 29.5 7.4 1.5

10.4 (X) 2.9 35 34.7 4.0 0.8

24.0 (K) 1.3 80 42.0 1.7 0.3

12.0 (Ku) 2.5 40 36.0 3.5 0.7

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.

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)

More about SRT activities #1The following is extracted from

http://www.haystack.mit.edu/edu/undergrad/srt/index.html

The VSRTAlan’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

Some VSRT Documentation – one of the parts

lists

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

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

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.

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.

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 generatingDiSEqC commands.

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)

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, K3IOmailto: K3IO@verizon.net