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Chapter 23

Space

Communications

An Amateur Satellite Primer

Most amateurs are familiar with repeater

stations that retransmit signals to provide

wider coverage. Repeaters achieve this

by listening for signals on one frequency

and immediately retransmitting whatever

they hear on another frequency. Thanks

to repeaters, small, low-power radios can

communicate over thousands of square ki-

lometers. Unfortunately, many amateurs are

not

familiar with the best repeaters that have

ever existed. These are the amateur satel-

lites that hams have been using for decades.

(See the sidebar “Tired of the Same Old

QSOs?”)

This is essentially the function of an ama-

teur satellite as well. Of course, while a

repeater antenna may be up to a few hundred

meters above the surrounding terrain, the

satellite is hundreds or thousands of

kilo-

meters

above the surface of the Earth. The

area of the Earth that the satellite’s signals

can reach is therefore much larger than the

coverage area of even the best Earth-bound

repeaters. It is this characteristic of satel-

lites that makes them attractive for com-

munication. Most amateur satellites act as

analog repeaters, retransmitting CW and

voice signals exactly as they are received,

as packet store-and-forward systems that

receive whole messages from ground sta-

tions for later relay, or as specialized Earth-

looking camera systems that can provide

some spectacular views. See

Fig 23.2,

image of a town in the western US.

Amateur satellites have a long history

of performing worldwide communica-

tions services for amateurs. See the sidebar

N1JEZ

Fig 23.1—N1JEZ's portable microwave satellite station.

“Amateur Satellite History.”

LINEAR TRANSPONDERS AND THE

PROBLEM OF POWER

Most analog satellites are equipped with

linear transponders.

These are devices

that retransmit signals within a band of

frequencies, usually 50 to 250 kHz wide,

known as the

passband.

Since the linear

transponder retransmits the entire band,

a number of signals may be retransmit-

ted simultaneously. For example, if three

SSB signals (each separated by as little

as 5 kHz) were transmitted to the satel-

Space Communications

23.1

Tired of the Same Old QSOs? Break out of Orbit and Set your Course for the

“Final Frontier”

Satellite-active hams comprise a relatively small segment

of our hobby, primarily because of an unfortunate ﬁction that

has been circulating for many years—the myth that operating

through amateur satellites is overly difﬁcult and expensive.

Like any other facet of Amateur Radio, satellite hamming is as

expensive as you allow it to become. If you want to equip your

home with a satellite communication station that would make a

NASA engineer blush, it will be expensive. If you want to simply

communicate with a few low-Earth-orbiting birds using less-than-

state-of-the-art gear, a satellite station is no more expensive than

a typical HF or VHF setup. In many cases you can communicate

with satellites using your present station equipment—no addi-

tional purchases are necessary.

Does satellite hamming impose a steep learning curve? Not re-

ally. You have to do a bit of work and invest some brain power

to be successful, but the same can be said of DXing, contest-

ing, trafﬁc handling, digital operating or any other specialized

endeavor. You are, after all, communicating with a

spacecraft!

The rewards for your efforts are substantial, making sat-

ellite operating one of the most exciting pursuits in Amateur

Radio. There is nothing like the thrill of hearing someone

responding to your call from a thousand miles away and

knowing that he heard you through a satellite. (The same

goes for the spooky, spellbinding effect of hearing your own

voice echoing through a spacecraft as it streaks through

the blackness of space.) Satellite hamming will pump the

life back into your radio experience and give you new goals

to conquer.

Fig 23.3—A linear transponder acts much like a repeater, except that it relays an entire

group of signals, not just one signal at a time. In this example the satellite is receiving

three signals on its 23-cm uplink passband and retransmitting them on its 13-cm

downlink passband.

Table 23.1

Satellite Operating Modes

Satellite Band Designations

10 meters (29 MHz): H

2 meters (145 MHz): V

70 cm (435 MHz): U

23 cm (1260 MHz): L

13 cm (2.4 GHz): S

5 cm (5.6 GHz): C

3 cm (10 GHz): X

Operating Modes (Uplink/Downlink)

V/H (2 meters/10 meters)

H/V (10 meters/2 meters)

U/V (70 cm/2 meters)

V/U (2 meters/70 cm)

U/S (70 cm/13 cm)

U/L (70 cm/23 cm)

L/S (23 cm/13 cm)

L/X (23 cm/3 cm)

C/X (5 cm/3 cm)

Old Designation

Fig 23.2—UO-36 captured this image of a

well-known city in the western US. Need a

hint? Think “Caesar’s Palace.”

lite, the satellite would retransmit all three

signals—still separated by 5 kHz each

(see

Fig 23.3).

Just like a terrestrial re-

peater, the retransmissions take place on

frequencies that are different from the ones

on which the signals were originally

received.

Some linear transponders invert the uplink

signals. In other words, if you transmit to the

satellite at the

bottom

of the uplink passband,

23.2

Chapter 23

your signal will appear at the

top

of the down-

link passband. In addition, if you transmit in

lower sideband (LSB), your downlink signal

will be in upper sideband (USB). See

Fig

23.4.

Satellite passbands are usually oper-

ated according to the courtesy band plan, as

shown. Transceivers designed for satellite

use usually include features that cope with

this confusing ﬂip-ﬂop.

Over the years, the number of amateur

Fig 23.4—The OSCAR satellite band plan

allows for CW-only, mixed CW/SSB, and

SSB-only operation. Courteous operators

observe this voluntary band plan at all

times.

Fig 23.6—Tabular output from an orbit prediction program showing time and position

information for AO-16.

Fig 23.7—The

communications

range circles, or

“footprints” over

North America.

Fig 23.5—An example of a satellite in a

high, elliptical orbit.

bands available on satellites has increased.

To help in easily identifying these bands,

a system of “Modes” has been created.

In the early years reference to these

Modes was by a single letter (Mode A,

Mode B, etc), but with the launch of more

satellites the opportunities greatly increased

and it was necessary to show both the

uplink and downlink bands. See

Table 23.1,

Satellite Operating Modes.

Linear transponders can repeat any type of

signal, but those used by amateur satellites

are primarily designed for SSB and CW. The

reason for the SSB and CW preference has a

lot to do with the hassle of generating pow-

er in space. Amateur satellites are powered

by batteries, which are recharged by solar

cells. “Space rated” solar arrays and batter-

ies are very expensive. They are also heavy

and tend to take up a substantial amount of

space. Thanks to meager funding, hams don’t

have the luxury of launching satellites with

large power systems such as those used by

commercial birds. We have to do the best

we can within a much more limited “power

budget.”

So what does this have to do with SSB

or any other mode? Think

duty cycle—the

amount of time a transmitter operates at full

output. With SSB and CW the duty cycle is

quite low. A linear satellite transponder can

retransmit many SSB and CW signals while

still operating within the power generating

limitations of an amateur satellite. It hardly

breaks a sweat.

Now consider FM. An FM transmitter op-

erates at a 100% duty cycle, which means it

is generating its full output with every trans-

mission. Imagine how much power a linear

transponder would need to retransmit, say,

a dozen FM signals—all demanding 100%

output!

Having said all that, there

are

a few, very

popular FM repeater satellites. However, they

do not use linear transponders. They retrans-

mit only one signal at a time.

FINDING A SATELLITE

Before you can communicate through a

satellite, you have to know what satellites are

available and when they are available. (See

sidebar “Current Amateur Satellites.”) This

isn’t quite as straightforward as it seems.

Amateur satellites do not travel in geo-

stationary orbits like many commercial

and military spacecraft. Satellites in geo-

stationary orbits cruise above the Earth’s

equator at an altitude of about 35,000

kilometers. From this vantage point the satel-

lites can “see” almost half of our planet. Their

speed in orbit matches the rotational speed of

the Earth itself, so the satellites appear to be

Space Communications

23.3

Amateur Satellite History

The Amateur Radio satellite

program began with the de-

sign, construction and launch

of OSCAR I in 1961 under the

auspices of the Project OSCAR

Association in California. The

acronym “OSCAR,” which has

been attached to almost all Ama-

teur Radio satellite designations

on a worldwide basis, stands

for

Orbiting Satellite Carrying

Amateur Radio.

Project OSCAR

was instrumental in organizing

the construction of the next three

Amateur Radio satellites—

OSCARs II, III and IV.

In 1969, the Radio Amateur

Satellite Corporation (AMSAT)

was formed in Washington, DC.

AMSAT has participated in the

vast majority of amateur satel-

lite projects, both in the United

States and internationally, begin-

ning with the launch of OSCAR

5. Now, many countries have

their own AMSAT organizations,

such as AMSAT-UK in England,

AMSAT-DL in Germany, BRAM-

SAT in Brazil and AMSAT-LU in

Argentina. All of these organiza-

tions operate independently but

may cooperate on large satellite

projects and other items of inter-

est to the worldwide Amateur Ra-

dio satellite community. Because

of the many AMSAT organiza-

tions now in existence, the US

AMSAT organization is frequently

designated AMSAT-NA.

Beginning with OSCAR 6,

amateurs started to enjoy the

use of satellites with lifetimes

measured in years as opposed to

weeks or months. The operational

lives of OSCARs 6, 7, 8 and 9,

for example, ranged between

four and eight years. All of these

satellites were low Earth orbiting

(LEO) with altitudes approximate-

ly 800-1200 km. LEO Amateur

Radio satellites have also been

launched by other groups not

associated with any AMSAT

organization such as the Radio

Sputniks 1-8 and the ISKRA 2

and 3 satellites launched by the

former Soviet Union.

The short-lifetime LEO satel-

lites (OSCARs I through IV and

5) are sometimes designated

the

Phase I

satellites, while the

long-lifetime LEO satellites are

sometimes called the

Phase II

satellites. There are other conven-

tions in satellite naming that are

useful to know. First, it is common

practice to have one designa-

tion for a satellite before launch

and another after it is success-

fully launched. Thus, OSCAR 40

(discussed later) was known as

Phase 3D before launch. Next,

the AMSAT designator may be

added to the name, for example,

AMSAT-OSCAR 40, or just AO-40

for short. Finally, some other des-

ignator may replace the AMSAT

designator such as the case with

Japanese-built Fuji-OSCAR 29

(FO-29).

In order to provide wider cover-

age areas for longer time periods,

the high-altitude Phase 3 series

was initiated. Phase 3 satellites

often provide 8-12 hours of com-

munications for a large part of the

Northern Hemisphere. After los-

ing the ﬁrst satellite of the Phase

3 series to a launch vehicle failure

in 1980, AO-10 was successfully

launched and became operational

in 1983. AO-13, the follow-up to

the AO-10 mission, was launched

in 1988 and re-entered the atmo-

sphere in 1996. The successor to

AO-13, AO-40 was launched on

November 16, 2000 from Kourou,

French Guiana.

Satellites providing store-and-

forward communication services

using packet radio techniques

are generically called

PACSATs.

Files stored in a PACSAT mes-

sage system can be anything

from plain ASCII text to digitized

pictures and voice.

The ﬁrst satellite with a digital

store-and-forward feature was

UoSAT-OSCAR 11. UO-11’s

Digital Communications Experi-

ment (DCE) was not open to the

general Amateur Radio com-

munity although it was utilized by

designated “gateway” stations.

The ﬁrst satellite with store-and-

forward capability open to all

amateurs was the Japanese Fu-

ji-OSCAR 12 satellite, launched

in 1986. FO-12 was succeeded

by FO-20, launched in 1990, and

FO-29, launched in 1996.

By far the most popular store-

and-forward satellites are the

PACSATs

utilizing the PACSAT

Broadcast Protocol. These

PACSATs fall into two general

categories — the

Microsats,

based on technology developed

by AMSAT-NA, and the

UOSATs,

based on technology developed

by the University of Surrey in

the UK. While both types are

physically small spacecraft, the

Microsats represent a truly in-

novative design in terms of size

and capability. A typical Microsat

is a cube measuring 23 cm (9

in) on a side and weighing about

10 kg (22 lb). The satellite will

contain an onboard computer,

enough RAM for the message

storage, two to three transmit-

ters, a multichannel receiver,

telemetry system, batteries and

the battery charging/power con-

ditioning system.

Amateur Radio satellites have

evolved to provide three primary

types of communication services

— analog transponders for real-

time CW and SSB communica-

tion, digital store-and-forward for

non real-time communication,

and direct “bent-pipe” single-

channel FM repeaters. Which

of these types interest you the

most will probably depend on

your current Amateur Radio

operating habits. Whatever your

preference, this section should

provide the information to help

you make a successful entry into

the specialty of amateur satellite

communications.

23.4

Chapter 23

Current Operational Amateur Satellites

OSCAR 7,

AO-7, was launched

November 15, 1974 by a Delta

2310 from Vandenberg, CA. AO-7’s

operating status is semi-operational

in sunlight only. After being declared

dead in mid 1981 due to battery fail-

ure, AO-7 has miraculously sprung

back to life. It will only be on when in

sunlight and off in eclipse. AO-7 will

reset each orbit and may not turn on

each time.

OSCAR 11, UO-11,

a scientiﬁc/

educational low-orbit satellite, was

built at the University of Surrey in

England and launched on March

1, 1984. This UoSat spacecraft has

also demonstrated the feasibility

of store-and-forward packet digital

communications and is semi-opera-

tional with telemetry downlinks only.

OSCAR 16, AO-16,

also known as

PACSAT, was launched in January

1990. A digital store-and-forward

packet radio ﬁle server, it has an

experimental S-band beacon at

2401.143 MHz. AO-16 is only semi-

operational with the 1200-baud

digipeater for APRS service.

OSCAR 27, AO-27,

was launched

in September 1993 along with

OSCAR 26. It features a mode V/U

analog FM repeater. Because of the

need to conserve power, OSCAR

27 is usually only available during

daylight passes.

OSCAR 44, NO-44,

also known as

PCSAT was launched on September

30, 2001 from Kodiak, Alaska. PC-

SAT is a 1200-baud APRS digipeater

designed for use by stations using

hand-held or mobile transceivers.

The operational status of PCSAT is

uncertain and subject to change due

to power availability.

OSCAR 50, SO-50

also known

as SAUDISAT-1C, was launched

December 20, 2002 aboard a con-

verted Soviet ballistic missile from

Baikonur Cosmodrome. SO-50 car-

ries several experiments, including a

mode U/V FM amateur repeater. The

repeater is available to amateurs as

power permits, using a 67.0 Hz uplink

tone for on-demand activation.

OSCAR 51,

also known as

Echo,

was launched on June 29, 2004 from

the Baikonur Cosmodrome. Echo

carries an FM repeater capable of

144 MHz and/or 1.2 GHz uplink with

a 435 MHz and/or 2.4GHz downlink.

The satellite also includes an AX.25

digital PACSAT BBS and a PSK31

uplink on 28 MHz.

VUSat-OSCAR 52 was launched

on May 5, 2005. Within 24 hours its

Mode U/V transponder was open

for business and hams were report-

ing excellent signals. The ﬁrst Indian

Amateur Radio satellite carries two

1-W linear transponders for SSB and

CW communication, although only

one transponder is operational at a

time. OSCAR 52 travels in a polar

sun-synchronous orbit at an altitude

of 632 × 621 km with an inclination of

97.8 deg with respect to the equator.

Ten satellites reached orbit April

28, 2008, aboard an Indian PSLV-

C9 rocket launched from the Satish

Dhawan Space Center. The primary

payloads were India’s CARTOSAT-2A

and IMS-1 satellites. In addition to the

NLS-5 and RUBIN-8 satellites, the

rocket carried six CubeSat research

satellites, all of which communicate

using Amateur Radio frequencies:

The

SEEDS

satellite was designed

and built by students at Japan’s

Nihon University. SEEDS down-

loads telemetry in Morse code and

1200-baud FM AFSK packet radio at

437.485 MHz. The satellite also has

slow-scan TV (SSTV) capability.

AAUSAT-II

was the creation of a

student team at Aalborg University in

Denmark. It downlinks scientiﬁc tele-

metry at 437.425 MHz using 1200 or

9600-baud packet.

Can-X2

was a product of students

at the University of Toronto Institute

for Aerospace Studies, Space Flight

Laboratory (UTIAS/SFL). Can-X2

downlinks telemetry at 437.478 MHz

using 4 kbps GFSK, but the downlink

is active only when the satellite is

within range of the Toronto ground

station.

Compass-One

was designed and

built by students at Aachen Univer-

sity of Applied Sciences in Germany.

The satellite features a Morse code

telemetry beacon at 437.275 MHz.

Compass-One also provides a

packet radio data downlink, which

includes image data, at

437.405 MHz.

Cute 1.7 + APDII

is a satellite

created by students at the Tokyo

Institute of Technology. This satellite

not only provides telemetry, but also

offers a 9600-baud packet store-and-

forward message relay with an uplink

at 1267.6 MHz and a downlink at

437.475 MHz.

Dutch-OSCAR 64

was designed

and built by students at Delft

University of Technology in the

Netherlands. It includes an SSB/CW

linear transponder. DO-64 down-

links 1200-baud packet telemetry at

145.870 MHz. The linear transpon-

der has an uplink passband from

435.530 to 435.570 MHz and a cor-

responding downlink passband from

145.880 to 145.920 MHz.

Note: For the latest information on

operational amateur satellites, see

AMSAT’s Satellite Status Summary

page on the Web at

www.amsat.

org.

“parked” at ﬁxed positions in the sky. They

are available to send and receive signals 24

hours a day over an enormous area.

Of course, amateur satellites

could

placed in geostationary orbits. The problem

isn’t one of physics; it’s money and politics.

Placing a satellite in geostationary orbit and

keeping it on station costs a great deal of

money—more than any one amateur satellite

organization can afford. An amateur satellite

group could ask similar groups in other areas

of the world to contribute money to a geo-

stationary satellite project, but why should

they? Would you contribute large sums of

money to a satellite that may never “see” your

part of the world? Unless you are blessed

with phenomenal generosity, it would seem

unlikely!

Instead, all amateur satellites are either

low-Earth orbiters (LEO), or they travel in

very high, elongated orbits. See

Fig 23.5.

Either way, they are not in ﬁxed positions

in the sky. Their positions relative to your

station change constantly as the satellites

zip around the Earth. This means that you

need to predict when satellites will appear

in your area, and what paths they’ll take as

they move across your local sky.

You’ll be pleased to know that there is

software available that handles this predic-

Space Communications

23.5

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