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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 re-

peaters, small, low-power radios can com-

municate over thousands of square

kilometers. Unfortunately, many ama-

teurs are

not

familiar with the best repeat-

ers that have ever existed. These are the

amateur satellites that hams have been

using for 40 years. (See the sidebar “Tired

of the Same Old QSOs?”)

This is essentially the function of an

amateur satellite as well. Of course, while

a repeater antenna may be up to a few hun-

dred meters above the surrounding terrain,

the satellite is hundreds or thousands of

kilometers

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 character-

istic of satellites that makes them attrac-

tive for communication. Most amateur

satellites act as analog repeaters, retrans-

mitting CW and voice signals exactly as

they are received, as packet store-and-for-

ward systems that receive whole messages

from ground stations for later relay, or as

specialized Earth-looking camera systems

that can provide some spectacular views.

See

Fig 23.2,

an image of a town in the

western US.

Amateur satellites have a long history

of performing worldwide communications

N1JEZ

Fig 23.1—N1JEZ's portable microwave satellite station.

services for amateurs. See the sidebar

“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 retransmitted

simultaneously. For example, if three

SSB signals (each separated by as little

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 unfortu-

nate 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 additional purchases are necessary.

Does satellite hamming impose a steep learning curve? Not

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

power to be successful, but the same can be said of

DXing, contesting, traffic handling, digital operating or any

other specialized endeavor. You are, after all, communi-

cating with a

spacecraft!

The rewards for your efforts are substantial, making

satellite 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.

Fig 23.2—UO-36 captured this image of

a well-known city in the western US.

Need a hint? Think “Caesar’s Palace.”

as 5 kHz) were transmitted to the satellite,

the satellite would retransmit all three sig-

nals—still separated by 5 kHz each (see

Fig 23.3).

Just like a terrestrial repeater,

the retransmissions take place on frequen-

cies 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 trans-

23.2

Chapter 23

mit to the satellite at the

bottom

of the

uplink passband, your signal will appear

at the

top

of the downlink passband. In

addition, if you transmit in lower sideband

(LSB), your downlink signal will be in

upper sideband (USB). See

Fig 23.4.

Sat-

ellite passbands are usually operated ac-

cording 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

bands available on satellites has in-

creased. 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 opportuni-

ties greatly increased and it was neces-

sary to show both the uplink and down-

link bands. See

Table 23.1,

Satellite

Operating Modes.

Linear transponders can repeat any type

of signal, but those used by amateur satel-

lites are primarily designed for SSB and

CW. The reason for the SSB and CW pref-

erence has a lot to do with the hassle of

generating power in space. Amateur sat-

ellites are powered by batteries, which are

recharged by solar cells. “Space rated”

solar arrays and batteries are very expen-

sive. 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 com-

mercial birds. We have to do the best we

Table 23.1

Satellite Operating Modes

Frequency Band

Letter Designation

New Designation

Old Designation

(Transmit, First Letter;

Receive, Second Letter)

Mode U/V

Mode B

Mode V/U

Mode J

Mode U/S

Mode S

Mode L/U

Mode L

Mode V/H

Mode A

Mode H/S

Mode L/S

Mode L/X

Mode C/X

HF, 21-30 MHz

VHF, 144-148 MHz

UHF, 435-438 MHz

1.26-1.27 GHz

2.40-2.45 GHz

5.6 GHz

10.4 GHz

24 GHz

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.

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 tran-

sponder can retransmit many SSB and CW

signals while still operating within the

power generating limitations of an ama-

teur satellite. It hardly breaks a sweat.

Now consider FM. An FM transmitter

operates at a 100% duty cycle, which

means it is generating its full output with

every transmission. 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. How-

ever, they do not use linear transponders.

They retransmit only one signal at a time.

FINDING A SATELLITE

Before you can communicate through

a satellite, you have to know what satel-

lites are available and when they are

available. (See sidebar “Current Amateur

Satellites.”) This isn’t quite as straight-

forward 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

satellites 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 “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 prob-

lem isn’t one of physics; it’s money and

politics. Placing a satellite in geostation-

ary 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 simi-

lar groups in other areas of the world to

contribute money to a geostationary satel-

lite 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!

Fig 23.5—An example of a satellite in a

high, elliptical orbit.

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 pre-

diction task very nicely. A bare-bones pro-

gram will provide a schedule for the

satellite you choose. A very simple sched-

ule might look something like

Fig 23.6,

showing the antenna pointing angles for

each minute of a pass for AO-16.

The time is usually expressed in UTC.

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

position information for AO-16.

Space Communications

23.3

Amateur Satellite History

The Amateur Radio satellite

program began with the design,

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

Amateur Radio satellite designa-

tions 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.

The Radio Amateur’s Satellite

Handbook

, published by ARRL

has details of the early days of

the amateur space program.

In 1969, the Radio Amateur

Satellite Corporation (AMSAT)

was formed in Washington, DC.

AMSAT has participated in the

vast majority of amateur satellite

projects, both in the United

States and internationally,

beginning with the launch of

OSCAR 5. Now, many countries

have their own AMSAT organiza-

tions, such as AMSAT-UK in

England, AMSAT-DL in Ger-

many, BRAMSAT in Brazil and

AMSAT-LU in Argentina. All of

these organizations operate

independently but may cooper-

ate on large satellite projects

and other items of interest to the

worldwide Amateur Radio

satellite community. Because of

the many AMSAT organizations

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 opera-

tional 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 alti-

tudes approximately 800-1200

km. LEO Amateur Radio satel-

lites 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

conventions in satellite naming

that are useful to know. First, it

is common practice to have one

designation for a satellite before

launch and another after it is

successfully 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

designator may replace the

AMSAT designator such as the

case with Japanese-built Fuji-

OSCAR 29 (FO-29).

In order to provide wider

coverage areas for longer time

periods, the high-altitude Phase

3 series was initiated. Phase 3

satellites often provide 8-12

hours of communications for a

large part of the Northern

Hemisphere. After losing the first

satellite of the Phase 3 series to

a launch vehicle failure in 1980,

AO-10 was successfully

launched and became opera-

tional in 1983. AO-13, the follow-

up to the AO-10 mission, was

launched in 1988 and re-entered

the atmosphere 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

message system can be any-

thing 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

Experiment (DCE) was not

open to the general Amateur

Radio community although it

was utilized by designated

“gateway” stations. The first

satellite with store-and-forward

capability open to all amateurs

was the Japanese Fuji-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 technol-

ogy 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 innovative

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

conditioning system.

Amateur Radio satellites

have evolved to provide three

primary types of communica-

tion services — analog tran-

sponders for real-time CW and

SSB communication, 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 operat-

ing 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

AO-16 will appear above your horizon

beginning at 0516 UTC on January 30. The

bird will “rise” at an azimuth of 164°, or

approximately south-southeast of your

station. The elevation refers to the

satellite’s position above your horizon in

degrees—the higher the better. A zero-

degree elevation is right on the horizon;

90° is directly overhead.

By looking at this schedule you can see

that the satellite will appear in your south-

southeastern sky at 0516 UTC and will rise

Fig 23.7—The

communications

range circles, or

“footprints” over

North America.

quickly to an elevation of 70° by 0524.

The satellite’s path will curve further to

the east and then directly to the north as it

rises. Notice how the azimuth shifts from

164° at 0516 UTC to 0° at 0524. This is

nearly a direct overhead pass of AO-16

and it sets in the north-northwest at 348°.

The more sophisticated the software, the

more information it usually provides in the

schedule table. The software may also dis-

play the satellite’s position graphically as

a moving object superimposed on a map of

the world. Some of the displays used by

satellite prediction software are visually

stunning! This view,

Fig 23.7,

is provided

Nova

for

Windows,

from Northern

Lights Software Associates.

Satellite prediction software is widely

available on the Web. Some of the simpler

programs are freeware. The AMSAT-NA

Web site has the largest collection of satel-

lite software for just about any computer

you can imagine. Most AMSAT software

isn’t free, but the cost is reasonable and the

funds support amateur satellite programs.

Whichever software you choose, there

are two key pieces of information you must

provide before you can use the programs:

(1)

Your position.

The software must

have your latitude and longitude before it

can crank out predictions for your sta-

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

failure, 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 operational

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 26, IO-26,

was launched

on September 26, 1993 is semi-

operational and now serves as a

1200-baud digipeater for APRS

service.

RS 15,

launched in December

1994, is a Mode V/H spacecraft; its

uplink is on the 2m band, and its

downlink is on 10m.

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 29, FO-29,

launched from

Japan in 1996, in a low earth orbit. It

operates with a mode V/U analog

transponder.

OSCAR 44, NO-44,

also known as

PCSAT was launched on September

30, 2001 from Kodiak, Alaska.

PCSAT 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

converted Soviet ballistic missile

from Baikonur Cosmodrome. SO-50

carries several experiments, includ-

ing a mode U/V FM amateur re-

peater. 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 a 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 reporting

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.

Space Communications

23.5

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