Download AMSAT 1m Dish - Del Mar North

Some ideas for antennas for
AMSAT’s next generation of
satellites
____________
describing some unfinished work in progress
Tom Clark, K3IO
mailto: [email protected]
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: 2300-2310
13 cm: 2390-2450
10
60
2400-2450
50
9 cm: 3300-3500
200
3400-3410 *
10
5 cm: 5650-5925
275
5650-5670 
5830-5850 
20
20
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 , cm
1M 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 #1
The following is extracted from
http://www.haystack.mit.edu/edu/undergrad/srt/index.html
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
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 bidirectional 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 generating
DiSEqC 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, K3IO
mailto: [email protected]