18.pdf
(
1910 KB
)
Pobierz
Contents
18.4 Glossary of FM and Repeater
Terminology
18.5 D-STAR Repeater Systems
18.5.1 D-STAR Station IDs
18.5.2 Station Routing
18.5.3 Enhancing D-STAR Operation with
DPlus
18.5.4 D-STAR Repeater Hardware
18.6 References and Further Reading
18.1 A Brief History
18.2 Repeater Overview
18.2.1 Types of Repeaters
18.2.2 Advantages of Using a Repeater
18.2.3 Repeaters and the FCC
18.3 FM Voice Repeaters
18.3.1 FM Repeater Operation
18.3.2 Home and Mobile Equipment
18.3.3 Coded Squelch and Tones
18.3.4 Frequency Coordination and
Band Plans
18.3.5 Linked Repeaters
Chapter
18
Repeaters
18.1 A Brief History
Few hams today don’t operate at least some VHF/UHF FM, and for many hams, FM
is
Amateur Radio. That wasn’t always the case.
Until the late 1960s, the VHF and UHF Amateur Radio bands were home to a relatively
small number of highly skilled operators who used CW and SSB for long distance com-
munication and propagation experiments. This operation used just a small fraction of the
spectrum available at 50 MHz an d above. A somewhat larger number of hams enjoyed low
power, local operation with AM transceivers on 6 and 2 meters. Our spectrum was under-
utilized, while public safety and commercial VHF/UHF two-way operation, using FM and
repeaters, was expanding rapidly.
The business band grew so rapidly in the early 1960s that the FCC had to create new chan-
nels by cutting the existing channels in half. Almost overnight, a generation of tube-type,
crystal-controlled FM equipment had to be replaced with radios that met the new channel
requirements. Surplus radios fell into the hands of hams for pennies on the original dollar.
This equipment was designed to operate around 150 MHz and 450 MHz, just above the
2-meter and 70-cm amateur bands. It was fairly easy to order new crystals and retune them
to operate inside the ham bands. Hams who worked in the two-way radio industry led the
way, retuning radios and building repeaters that extended coverage. Other hams quickly fol-
lowed, attracted by the noise-free clarity of FM audio, the inexpensive equipment, and the
chance to do something different.
That initial era didn’t last long. The surplus commercial equipment was cheap, but it was
physically large, ran hot and consumed lots of power. By the early 1970s, manufacturers
recognized an untapped market and began building solid-state equipment specifically for the
Amateur Radio FM market. The frequency synthesizer, perfected in the mid-1970s, eliminated
the need for crystals. The stage was set for an explosion that changed the face of Amateur
Radio. Manufacturers have added plenty of new features to equipment over the years, but
the basic FM operating mode remains the same.
In the 1980s, hams experimenting with data communications began modulating their FM
radios with tones.
Packet radio
spawned a new system of
digipeaters
(digital repeaters).
Digitized audio has been popular since audio compact discs (CDs) were introduced in the
1980s. In the 1990s, technology advanced enough to reduce the bandwidth needed for digital
audio, especially voice, to be carried over the Internet and narrowband radio circuits. The
first digital-voice public safety radio systems (called APCO-25) appeared, and a variety of
Internet voice systems for conferencing and telephone-like use were developed.
Hams are using VHF/UHF digital voice technology, too. The Japan Amateur Radio League
(JARL) developed a true ham radio standard called D-STAR, a networked VHF/UHF repeater
system for digital voice and data that is beginning to make inroads around the world. Hams
are also using surplus first generation APCO-25 radios and have adapted Internet voice
systems for accessing and linking repeaters.
For decades, FM has been
a dominant mode of Amateur
Radio operation. FM and repeat-
ers fill the VHF and UHF bands,
and most hams have at least one
handheld or mobile FM radio.
Thousands of repeaters through-
out the country provide reliable
communication for amateurs
operating from portable, mobile
and home stations. Now, Ama-
teur Radio is beginning to see
the emergence of fully digital
voice modulation, though analog
is expected to dominate for the
foreseeable future. The first part
of this chapter, by Paul M. Danzer,
N1II, with contributions by Gary
Pearce, KN4AQ, describes FM
voice repeaters. Later sections,
contributed by Jim McClellan,
N5MIJ, and Pete Loveall, AE5PL,
of the Texas Interconnect Team,
cover more recent developments
in D-STAR digital voice and data
repeaters.
18.2 Repeater Overview
Amateurs learned long ago that they could get much better use from their mobile and
portable radios by using an automated relay station called a
repeater
. Home stations benefit
Repeaters
18.1
as well — not all hams are located near the
highest point in town or have access to a tall
tower. A repeater, whose basic idea is shown
in
Fig 18.1
, can be more readily located where
the antenna system is as high as possible and
can therefore cover a much greater area.
HBK05_15-013
Transmit
146.94
Receive
146.34
Transmit
146.94
146.34
Repeater
18.2.1 Types of Repeaters
The most popular and well-known type of
amateur repeater is an FM voice system on
the 144 or 440 MHz bands. Amateurs operate
many repeaters on the 29, 50, 222, 902 and
1240 MHz bands as well, but 2 meters and
70 cm are the most popular. Tens of thou-
sands of hams use mobile and handheld
radios for casual ragchewing, emergency
communications, public service activities or
just staying in touch with their regular group
of friends during the daily commute.
FM is still the mode of choice for voice
repeaters, as it was in commercial service,
since it provides a high degree of immunity
to mobile noise pulses. Operations are
chan-
nelized
— all stations operate on the same
transmit frequency and receive on the same
receive frequency. In addition, since the re-
peater receives signals from mobile or fixed
stations and retransmits these signals simulta-
neously, the transmit and receive frequencies
are different, or
split.
Direct contact between
two or more stations that listen and transmit
on the same frequency is called operating
simplex
.
Individuals, clubs, emergency commu-
nications groups and other organizations
all sponsor repeaters. Anyone with a valid
amateur license for the band can establish a
repeater in conformance with the FCC rules.
No one owns specific repeater frequencies,
but nearly all repeaters are
coordinated
to
minimize repeater-to-repeater interference.
Frequency coordination and interference are
discussed later in this chapter. Operational
aspects are covered in more detail in
The
ARRL Operating Manual
.
Typical 2Meter
Repeater
Receive
146.94
Transmit
146.34
Receive
146.94
Transmit
146.34
Fig 18.1 — Typical 2-m repeater, showing mobile-to-mobile communication through a
repeater station. Usually located on a hill or tall building, the repeater ampliies and
retransmits the received signal on a different frequency.
Fig 18.2 — In the upper diagram, stations A and B cannot communicate because their
mutual coverage is limited by the mountains between them. In the lower diagram,
stations A and B can communicate because the coverage of each station falls within
the coverage of repeater C, which is on a mountaintop.
BEYOND FM VOICE
In addition to FM voice, there are several
other types of ham radio repeaters.
ATV (amateur TV)
— ATV repeaters
are used to relay wideband television sig-
nals in the 70 cm and higher bands. They
are used to extend coverage areas, just like
voice repeaters. ATV repeaters are often set
up for
crossband
operation, with the input
on one band (say, 23 cm) and the output on
another (say, 70 cm). More information on
ATV repeaters may be found in the
Image
Communications
chapter.
AM and SSB
— There is no reason to limit
repeaters to FM. There are a number of other
modulation-type repeaters, some experimen-
tal and some long-established.
Digital voice
— Repeaters for D-STAR
Fig 18.3 — In the Rocky Mountain
west, handheld transceivers can
often cover great distances, thanks
to repeaters located atop high
mountains.
(photo courtesy KCØETU
and KØNR)
18.2
Chapter 18
digital voice and data signals are discussed
later in this chapter. There are also some P-25
repeaters operating in the Amateur service
(see the
Digital Communications
chapter
for additional information.)
Digipeaters
— Digital repeaters used pri-
marily for packet communications, including
APRS (the Amateur Packet/position Report-
ing System). They can use a single channel
(single port) or several channels (multi-port)
on one or more VHF and UHF bands. See the
Digital Modes
and
Digital Communica-
tions
chapters for details of these systems.
Multi-channel (wideband)
— Amateur
satellites are best-known examples. Wide
bandwidth (perhaps 50 to 200 kHz) is se-
lected to be received and transmitted so all
signals in bandwidth are heard by the satel-
lite (repeater) and retransmitted, usually on
a different VHF or UHF band. See the
Space
Communications
chapter for details.
repeater maintains the range or coverage we
want, despite our equipment deficiencies. If
both the handheld transceiver and the repeater
are at high elevations, for example, communi-
cation is possible over great distances, despite
the low output power and inefficient antenna
of the transceiver (see
Fig 18.3
).
Repeaters also provide a convenient meet-
ing place for hams with a common interest.
It’s usually geographic — your town, or your
club. A few repeaters are dedicated to a par-
ticular interest such as DX or passing traffic.
Operation is channelized, and usually in any
area you can find out which channel — or
repeater — to pick to ragchew, get highway
information or whatever your need or interest
is. The conventional wisdom is that you don’t
have to tune around and call CQ to make a
contact, as on the HF bands. Simply call on a
repeater frequency — if someone is there and
they want to talk, they will answer you. But
with a few dozen repeaters covering almost
any medium size town, you probably use the
scan function in your radio to seek activity.
their extended range, uniformly good cover-
age and visibility. Most repeaters are well
known — everyone active in an area with
suitable equipment knows the local repeater
frequencies.
18.2.3 Repeaters and the
FCC
The law in the United States changes over
time to adapt to new technology and changing
times. Since the early 1980s, the trend has
been toward deregulation, or more accurately
in the case of radio amateurs, self-regulation.
Hams have established band plans, calling
frequencies, digital protocols and rules that
promote efficient communication and inter-
change of information.
Originally, repeaters were licensed sepa-
rately with detailed applications and control
rules. Repeater users were forbidden to use
their equipment in any way that could be
interpreted as commercial. In some cases,
even calling a friend at an office where the re-
ceptionist answered with the company name
was interpreted as a problem.
The rules have changed, and now most
nonprofit groups and public service events
can be supported and businesses can be called
— as long as the participating radio amateurs
are not earning a living from this specific
activity.
We can expect this trend to continue. For
the latest rules and how to interpret them,
see
QST
and the ARRL Web site,
www.arrl.
org
.
18.2.2 Advantages of Using a
Repeater
When we use the term
repeater
we are
almost always talking about transmitters and
receivers on VHF or higher bands, where
radio-wave propagation is normally line of
sight. Don’t take “line of sight” too literally.
VHF/UHF radio signals do refract beyond
what you can actually see on the horizon,
but the phrase is a useful description. (See
the
Propagation of Radio Signals
chapter
for more information on these terms.)
We know that the effective range of VHF
and UHF signals is related to the height of
each antenna. Since repeaters can usually
be located at high points, one great advan-
tage of repeaters is the extension of coverage
area from low-powered mobile and portable
transceivers.
Fig 18.2
illustrates the effect of using a
repeater in areas with hills or mountains. The
same effect is found in metropolitan areas,
where buildings provide the primary block-
ing structures.
Siting repeaters at high points can also have
disadvantages. When two nearby repeaters
use the same frequencies, your transceiver
might be able to receive both. But since it
operates FM, the
capture effect
usually en-
sures that the stronger signal will capture
your receiver and the weaker signal will not
be heard — at least as long as the stronger
repeater is in use.
It is also simpler to provide a very sensitive
receiver, a good antenna system, and a slightly
higher power transmitter at just one location
— the repeater — than at each mobile, por-
table or home location. A superior repeater
system compensates for the low power (5 W
or less), and small, inefficient antennas that
many hams use to operate through them. The
EMERGENCY OPERATIONS
When there is a weather-related emergency
or a disaster (or one is threatening), most
repeaters in the affected area immediately
spring to life. Emergency operation and traf-
fic always take priority over other ham activi-
ties, and many repeaters are equipped with
emergency power sources just for these oc-
casions. See
Fig 18.4
.
Almost all Amateur Radio emergency or-
ganizations use repeaters to take advantage of
Fig 18.4 — During disasters, repeaters over a wide area are used solely for
emergency-related communication until the danger to life and property is past.
(photo courtesy WA9TZL)
Repeaters
18.3
18.3 FM Voice Repeaters
Repeaters normally contain at least the sec-
tions shown in
Fig 18.5
. Repeaters consist of
a receiver and transmitter plus a couple more
special devices. One is a
controller
that routes
the audio between the receiver and transmit-
ter, keys the transmitter and provides remote
control for the repeater licensee or designated
control operators.
The second device is the
duplexer
that lets
the repeater transmit and receive on the same
antenna. A high power transmitter and a sen-
sitive receiver, operating in close proximity
within the same band, using the same antenna,
present a serious technical challenge. You-
might think the transmitter would just blow
the receiver away. But the duplexer keeps the
transmit energy out of the receiver with a se-
ries of tuned circuits. Without a duplexer, the
receiver and transmitter would need separate
antennas, and those antennas would need to
be 100 or more feet apart on a tower. Some
repeaters do just that, but most use duplexers.
A 2 meter duplexer is about the size of a two-
drawer filing cabinet. See
Fig 18.6
.
Receiver, transmitter, controller, and
duplexer: the basic components of most
repeaters. After this, the sky is the limit on
imagination. As an example, a remote re-
ceiver site can be used to extend coverage
(
Fig 18.7
).
The two sites can be linked either by tele-
phone (“hard wire”) or a VHF or UHF link.
Once you have one remote receiver site it is
natural to consider a second site to better hear
those “weak mobiles” on the other side of town
(
Fig 18.8
). Some of the stations using the re-
peater are on 2 meters while others are on 440?
Just link the two repeaters! (
Fig 18.9
).
For even greater flexibility, you can add
an auxiliary receiver, perhaps for a NOAA
weather channel (
Fig 18.10
).
The list goes on and on. Perhaps that is why
so many hams have put up repeaters.
mission of
courtesy tones
. Suppose several
stations are talking in rotation — one fol-
lowing another. The repeater detects the end
of a transmission of one user, waits a few
seconds, and then transmits a short tone or
beep. The next station in the rotation waits
until the beep before transmitting, thus giv-
ing any other station wanting to join in a
brief period to transmit their call sign. Thus
the term
courtesy tone
— you are politely
pausing to allow other stations to join in the
conversation.
Another common repeater feature that
encourages polite operation is the
repeater
timer
. A 3-minute timer is actually designed
to comply with an FCC rule for remotely
controlled stations, but in practice the timer
serves a more social function. Since repeater
operation is channelized — allowing many
stations to use the same frequency — it is
polite to keep your transmissions short. If
18.3.1 FM Repeater
Operation
There are almost as many operating proce-
dures in use on repeaters as there are repeaters.
Only by listening can you determine the cus-
tomary procedures on a particular machine. A
number of common operating techniques are
found on many repeaters, however.
One such common technique is the trans-
Fig 18.6 — The W4RNC 2-m repeater
includes the repeater receiver, transmitter
and controller in the rack. The large object
underneath is the duplexer.
(photo courtesy KN4AQ)
Fig 18.5 — The basic components of a repeater station. In the early days of repeaters,
many were home-built. Today, most are commercial, and are far more complex than this
diagram suggests.
18.4
Chapter 18
Plik z chomika:
gaszek.karol
Inne pliki z tego folderu:
02.pdf
(5422 KB)
01.pdf
(3401 KB)
00.pdf
(458 KB)
03.pdf
(5244 KB)
07.pdf
(7630 KB)
Inne foldery tego chomika:
Zgłoś jeśli
naruszono regulamin