G3RUH Articles Index
These articles by James Miller are part of a growing
collection of articles taken from various
magazines and the AMSAT.ORG
mailing lists. Note that new articles are
usually added at the bottom.
- AO-13 Transponder Schedule
- The current and future AO-13 transponder schedule.
- AO-13 Telemetry Archives
- Daily Oscar-13 telemetry is archived continuously by the AO-13 command stations from their own data and that collected by several helpers. No decoder hardware is required to view these files, just a program such as P3C.EXE for MS-DOS, or P3TLM for MS-Windows, or !TLM13 for Acorn Risc Computers.
If you want to capture your own telemetry, you'll need hardware, and a file is available describing suitable equipment.
AO-13 Telemetry Block Format
AO-13 Whole Orbit Data format
AO-13 CRCC specification
- 30.6 Days hath September
- A discussion of date algorithms for computer programs, with examples.
Originally appeared in OSCAR News, December 1985.
- 10 Ways To Ensure Failure on Oscar-10
- Shows in ironic style how every decibel gained counts, and every
decibel squandered is a step into the noise. Originally appeared in
OSCAR News, April 1986.
- Phase 5 Satellites
- An original proposal for transponder spectral equalisation using digital
electronics (DSP) as a means of solving the "alligator" problem.
Originally appeared in OSCAR News, April 1986.
- Icom's IC-820H, A Satellite User's Perspective
- Review of a satellite "9600 baud data ready" radio - that isn't.
Originally appeared in OSCAR News, August 1994.
- Planning AO-13 Mode Schedules
- Explains in detail the constraints that lead to the schedules.
Originally appeared in OSCAR News, January 1989.
- Shannon, Coding and the Radio Amateur
The addition of redundant bits to a data byte achieves an increase in data
transmission reliability. You send more bits than you started with (and
use more bandwidth) so for a fixed transmitter power the intrinsic bit
error rate worsens. However the associated error correction schemes more
than make up for this apparent penalty. When space communication costs
are reckoned in millions of $$$ per dB, schemes that provide more bytes
for your buck are of the greatest importance. Their use in amateur radio
is close. This article is a brief introduction to coding.
Originally appeared in OSCAR News, February 1990.
- 1991, 1992, 1993 ...and all that
19xx January is that time of year for the annual pleas by users of ancient
software that they've run out of "siderial whatsits". Gives the table
until 2000, and shows you how to calculate it. (It's sidereal, by the way).
Originally appeared in OSCAR News, February 1991.
- Down Memory Lane?
Discussion of Oscar-13's memory EDAC system, and huge rise in memory error
rate that occured on 1994 May 13. Startling conclusion.
Originally appeared in OSCAR News, August 1994.
- The Shape of Bits To Come
This article is about bits, about bandwidth and about control of both.
What is the "raised cosine modulation" used on microsats AO-16/18/19? And
what is the RSM-8 on Rudak/AO-21? What PSK modulation does Fuji-20 use?
Come to that, what is BPSK, and similar abbreviations? Substantial
tutorial article, copiously illustrated. Originally appeared in
OSCAR News, April 1991.
- 9600 Baud Packet Radio Modem Design
The theoretical minimum audio bandwidth required to send 9600 baud binary
data is 4800 Hz. Since a typical NBFM radio has an unfiltered response
from zero to some 8 kHz, transmission of 9600 baud binary data is perfectly
possible through it. This paper describes a successful implementation.
Originally appeared in the Proceedings of the ARRL 7th Computer
Networking Conference, October 1988.
- The Earth Moved
The Earth does not appear to be in a fixed position as seen from the Moon.
Shows the wander, and discusses the implications for Lunar stations.
Originally appeared in OSCAR News, April 1994.
- PLAN-13 Satellite Position Calculation Program
The basic routines needed for satellite
calculations. Includes fundamental equations, explanation and heavily
commented listing. Shows how to compute Orbit, MA, mode, range, azimuth,
elevation, squint, range rate, doppler shift, height, sub-satellite point,
footprint circle, day numbers, dates, Sun's position, solar azimuth, solar
elevation, illumination, eclipses, visibility etc etc. Routines widely
used by other authors. Originally appeared in OSCAR News, October 1990
(revision of article from December 1983).
- Sun's Up
Comprehensive series describing the Sun's orbit, how it's modelled, and
its influence on satellite illumination (esp. AO-10), including eclipse
prediction. Originally appeared in OSCAR News December 1984, February
1985, and April 1985.
- Sensorship - A Question of Attitudes
Comprehensive series about spacecraft attitude determination, with
particular reference to AO-10 Sun and Earth sensors. Originally appeared
in OSCAR News, August 1985 and October 1985.
- The Re-Entry of Oscar-13
Without an atmosphere, Oscar-13 would collide with the Earth's crust
on 1997 Feb 03. But we do have an atmosphere, which means that the
satellite experiences a gradual retardation every perigee pass. Thus
re-entry will be sooner, approximately 1996 Dec 05. This paper
outlines the computer program and discusses the circumstances.
Originally appeared in the
Proceedings of the 12th annual Amsat Space Symposium, Orlando, Florida,
- Mode-S - Tomorrow's Downlink
Proposes the abandonment of 145 MHz for P3 satellite downlinks, and
shows why the logical choice is 2400 MHz. Originally appeared in
OSCAR News, October 1992.
- A 60 cm S-Band Dish Antenna
"Mode-S - Tomorrow's Downlink" proposed the abandonment of the 145 MHz band
for weak signal amateur satellite downlinks and sparked off much interest.
I explained why S-band (2.4 GHz) is unrivalled on every count as its
replacement, and described in outline a tiny 60 cm diameter dish that is
entirely adequate for Oscar-13. I many requests for more details.
This antenna is simple and entirely adequate for Oscar-13 reception.
Originally appeared in OSCAR News, April 1993.
- A 16 turn S-band helix antenna
This design represents the smallest practical antenna for Oscar-13
mode-S. Perfect beacon reception at all times is possible, and
acceptable SSB even at 43,000 km range. CW is effortless. Tools
required; ruler, hacksaw, file and hand-drill. Test equipment,
voltmeter. Skill level, nil. Just do it!
Orginally entitled: "Small iS beSteSt". Originally appeared in
OSCAR News, October 1993.
- Managing Oscar 13
The Oscar-13 satellite is 85 kg of spinning tri-lobed chassis. Outwardly
it's covered with solar panels, inwardly it's filled with batteries, a
control computer, navigation sensors and associated interface
electronics. In addition there are four linear transponders used for long
range SSB voice and CW amateur radio communications. The management
objective is to ensure that the former equipment is controlled in such a
way as to ensure the most efficient use of these transponders. A member of
the Phase 3 management team for nearly a decade, the author describes how
Originally appeared in OSCAR News, December 1993 and February 1994.
- Measure AO-13 Squint Directly!
Shows how to calculate squint angle directly from S-band beacon. The
AO-13 S-band antenna is offset from the spin axis, so range oscillates back
and forth once per revolution. Hence the beacon warbles a few Hz,
proportional to the magnitude of the squint angle.
Originally appeared in OSCAR News, February 1993.
- From Hardware to Vapourware:
AO-13 Re-Entry Plans
The presence of Earth's atmosphere at perigee robs AO-13 of energy, which
is dissipated in the form of heat. This will cause burn-up around mid-
December 1996. End-of-life effects are discernible as a) orbital period
decrease and b) changes of attitude, c) heating. The first two are already
observable. Aspects of AO-13's re-entry are explored in these notes. In
particular a re-orientation to the unfamiliar attitude Alon/Alat = 90/0 is
proposed from mid-August 1996.
Originally appeared in OSCAR News, June 1996.
- Oscar-13's Life and Death
Oscar-13 was launched from Kourou on 1988 Jun 15th on the first test flight
(V-22) of the Ariane 4 rocket, along with Panamsat and Meteosat P2. Eight
and a half years later AO-13 re-entered and burned up, on 1996 Dec 5th.
Originally appeared in OSCAR News, February 1997.
- Phase III Ranging System
Ranging is the process of measuring the distance from a station to a
satellite. Ranges made at different times, and from several locations are
used to determine the specifics of an orbit and compute Keplerian
elements. P3D, like its predecessors P3A, Oscar-10 and Oscar-13 is
supported by ground station software and hardware to enable this.
Originally appeared in OSCAR News, October 1997.
- The Experimental IHU-2 Aboard P3D
IHU-2 is intended to act as a future replacement for the current COSMAC-1802-
based flight computer (IHU) that has flown on all previous P3 missions and
indeed controls the AMSAT P3D satellite. The IHU-2 is aboard P3D as a
proof-of-technology experiment. Although in contact with other P3D
sub-systems, it will
not manage anything mission critical. These notes document the design from
inspiration in September 1997 to running hardware/software, April 1998.
Originally appeared in Proceedings of 13th Amsat-UK Colloquium 1998, Surrey,
- Oscar-40 FEC Telemetry
Phil Karn KA9Q has long argued that AMSAT should adopt the communication
strategies used routinely for several decades by NASA space missions. They
have now been implemented experimentally on Oscar-40. The results are
truly spectacular. Indeed we must surely adopt strong Forward Error Correction
(FEC) by default on future missions. This article describes the system, and
presents results with AO-40. Using FEC, if you can hear it, it decodes;
error-free! Originally appeared in OSCAR News, August 2003.
- Control Software for the Bochum Radio Telescope
Every ham secretly wants to play with a really big antenna ... I got my chance! The restoration of this 20m diameter antenna required a new control system. The author was invited to write the software. This article describes its evolution. Originally appeared in The Amsat Journal (USA), Nov/Dec 2005.
- Stereo A/B Spacecraft Telemetry Reception at Bochum
In early 2009 the Amsat-DL Bochum Antenna team received an invitation from
NOAA/JPL to partner others in downloading space weather data from the Stereo
spacecraft on a "best effort" basis. This has required the development of
hardware and software, remote control and dealing with the problems of
keeping a system running around the clock. We considered, and find, the
experience valuable training for the P5 mission operations. This article
describes what we did. Originally appeared in Amsat-DL Journal (DL), Jg. 37, No. 3, Sep 2010.
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Last modified: 2010 Aug 09