|
|
This is only a preview of the July 1992 issue of Silicon Chip. You can view 48 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Articles in this series:
Items relevant to "Multi-Station Headset Intercom; Pt.2":
|
Understanding the
world of CB radio
Have you wondered about becoming involved
with CB radio? Perhaps you are thinking about
buying a CB radio for that next country trip. If
so, this article for you. It gives the background
and history of CB radio and talks about the
2 71\.1Hz and UHF bands.
By HERB ZALLNER
CB Radio as we know it today had
its origins in the late 1950s, in the
USA. On 11th September, 1958, the
FCC inaugurated a "Class D" service,
allocating 23 channels between
26.965MHz and 27.255MHz. The service was designed to be used for specific purposes, none of which related
to hobbyist use. Interest in the new
service soon grew and within 12
months, over 40,000 operators had
been licensed.
This service ran until 1971 when it
was dissolved and users were allocated other more specific services.
In 1973, the USA was in the grip of
an oil crisis. Fuel supplies were scarce
and a 55mph speed limit was brought
to bear. For "truckers", who had al16
SILICON CHIP
ready been subjected to a price and
wage freeze at a time of rocketing
costs, the speed limit was the last
straw and they went on strike. Millions of Americans saw news bulletins showing truck drivers with 2way radios organising their blockades
of tollways and interstate highways.
Motorists bought CB sets to hear
the truckers telling one another, after·
the strike was over, where scarce pet_rol was available and where highway
patrol cars could be found. Citizen's
Band radio had been born.
By 1976, the FCC found it impossible to police the number of licensees
and "pirates" occupying the CB service and decided to lift most restrictions, including one which had previ-
ously prevented hobby use of the
band. The result was incredible.
Within the next eight months, one
million licenses were granted and
another million were granted within
the next three months.
The US CB band contained 23 channels in the 2 7MHz band and allowed
4 watts of AM power. The transceivers used a method of frequency generation called crystal synthesis or
"crystal plexing", which utilised 12
or 14 crystals and three oscillators to
cleverly create both transmit and receive frequencies. This was a great
saving in cost over the previous crystal controlled sets , which had used 46
crystals.
At last, affordable transceivers were
Above: the Uniden Pro 810e is an AM/
SSB base station for the 27MHz CB
band. Its features include separate
volume, squelch, RF gain & clarifier
controls, a noise blanker switch, a 7W
audio amplifier, a PA facility plus
external speaker provision, and an
illuminated signal/RF meter. (Dick
Smith Electronics).
Table 1: 27MHz CB Channels
18-CH Set
1
2
3
4
5
Designed for in-car use, the Uniden PRO 640e is a top-of-the-line AM/SSB-CB
radio. Among its many features are digital readout of channel number; a LED
bargraph for signal strength, RF output & SWR; & direct access to emergency
channel 9. It covers all 40 channels in the 27MHz band on AM, LSB & USB.
(Dick Smith Electronics).
available to the general public and by
1977 several organisations had made
submissions to the Australian government fo r the intro duction of an
official CB band. In the meantime,
this did not prevent the sale an d consequential illegal use of tens of thousands of CB transceivers using the US
23-channel system while the various
submissions w ere under review.
A further complication arose in
1976 when the USA service was expanded to 40 channels to cater for
increased demand. Finally, the Australian governm ent decided to implement a compromise 18-channel system proposed by Dick Smith as the
best alternative for local conditions.
This channel system was designed to
allow the maximum number of channels without causing interference to
existing services.
Table 1 shows the 18 and 40-channel frequency allocations.
After several years of successful operation of the 18 channel system , Australia followed the USA and implemented the same 40 channels in the
27MHz band. SSB operation by this
time was allowed and despite the regulatory restriction of" communications
only within Australia", the tantalis-
ing possibility of communicating with
another country added more appeal
to users of the service.
CB became an outlet for social communications, allowing users to communicate with others at no cost (other
than the initial licensing fees) and
without th e burden of the technical
examination required of amateur operators. After all, most enthusiasts
claimed that the radio spectrum was a
national resource and that they should
not be denied the right to use it for
social means. The service also provided low-cost communications for
business people, even considering the
lack of privacy and unpredictable
communications range, a result of
operating on the 27MHz band.
In 1977, Philips Industries proposed
a "personal radio" band utilising part
of the UHF spectrum and using FM as
the transmission mode in the 476477MHz range. It was envisaged that
this would eventually replace the
2 7MHz band service and, in the meantime, ease congestion of the 27MHz
band. It would also allow business
users the same communications facilities as the 2 7MHz service while
allowing some reuse of frequencies,
as a result of the 10-25km "line of
6
7
8
9
10
11
12
13
14
15
16
17
18
40-CH Set
Frequency
1
2
3
4
5
6
7
8
9
10
11
26.965
26.975
26.985
27.005
27.015
27.025
27.035
27.055
27.065
27.075
27.085
27.095
27.105
27.115
27.125
27.135
27.155
27.165
27.175
27. 185
27.195
27.205
27.215
27.225
27.255
27.235
27.245
27.265
27.275
27.285
27.295
27.305
27.315
27.325
27.335
27.345
27.355
27.365
27.375
27.385
27.395
27.405
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
sight" coverage achievable with a UHF
transceiver.
In the same year, Philips introduced
their "FM320" 40-channel UHF personal (CB) radio transceiver which ,
despite its high price, was an instant
success. Subsequently, in November
1979, Philips also installed the first
UHF CB repeater at Lysterfield in the
foothills of the Dandenong ranges.
Approved under an experimental
JULY 1992
17
Retailing for around the $450 mark, the Pearce-Simpson UF-2020 UHF CB has
microprocessor control to provide scanning & a range of other specialised
functions. The front panel can be mounted remotely, so that the main body of
the rig can be located anywhere within the vehicle.
license issued by the DOC, this allowed enhanced coverage beyond the
normal simplex limitations of a UHF
transceiver, thereby adding considerable appeal to the UHF service.
Thereafter followed an enormous
influx of imported UHF transceivers
and the formation of various CB clubs,
which subsequently installed UHF
repeaters all over Australia. In many
cases, UHF CB became a viable alternative to commercial 2-way radio, although this was not the intention of
licensing authorities. Table 2 lists the
channel frequencies in the UHF CB
band.
Today, there are over 400,000 licensed CB operators in Australia,
proof of the success of the service.
Both the 2 7MHz and UHF bands coexist, serving hobbyists and commercial users alike. Emergency monitor-
ing services exist in most country
towns and outback travellers use CB
radio for communications, as do farmers, truck drivers, commercial users
and many country police officers!
Selecting a CB set
The price of a CB transceiver ranges
from less than $50 for a basic AM
transceiver to several hundred dollars for a sophisticated SSB or UHF
"rig". Don't make a rush decision when
buying equipment; your purchase deserves some consideration. If the intended application is city use only,
UHF offers FM clarity and repeater
enhanced operation. Small antennas
can be used and there are plenty of
mobile transceivers from which to
choose.
If the application involves outback
communications, then an AM/SSB
The Uniden
Sundowner is
typical of CB
radios designed
for the UHF band.
It covers all 40
channels, features
digital readout of
channel number &
features duplex
switching for
operation through
a repeater station.
(Dick Smith
Electronics).
18
SILfCON CHTP
transceiver, able to take advantage of
the 27MHz propagation or "skip" conditions, is the best choice. After all,
when calling for help, the larger the
audience, the better!
Also, a longer antenna can more
easily be tolerated when driving in
the country, as there are less obstructions to interfere with a 3-metre whip
than in the city.
Base stations are available in both
27MHz and UHF, although the 27MHz
models are somewhat better presented
and often include SWR and output
power metering, in addition to an inbuilt 240V AC power supply.
Having selected a suitable transceiver, a suitable antenna must be chosen. The most popular 2 7MHz mobile
antenna is the helical whip. By winding a quarter wavelength of wire on a
fibreglass whip, antenna makers have
been able to achieve reasonable matching, radiation pattern and mechanical
flexibility. Both ground dependent
and independent antennas are available.
If the antenna is to be mounted on a
metallic car body, a ground dependent antenna is necessary. If the mounting position is such that a good
groundplane cannot be achieved (critical if the antenna radiation pattern is
to provide any gain), then a ground
independent antenna should be used.
Typical mounting locations for a
ground independent antenna would
be the rear bumper, mirror mounts or
the bullbar of a motor vehicle.
Base station users are well catered
for, with high gain (9dBd) collinear
antennas and directional Yagi antennas available for UHF users. 27MHz
operators can utilise full length halfwave antennas and more adventurous operators have even been known
to install rotatable Yagi antennas (quite
an undertaking at this frequency)!
Most CB antennas come equipped
with coaxial cable, however the quality of the cable used for UHF installations is critically important. Coaxial
cable used at UHF can be used at
27MHz but the reverse is not always
true. the loss of signal through a low
quality coaxial cable at 27MHz is of
little consequence but at UHF it can
reduce transmitter output power and
receiver sensitivity by 50%.
Likewise, coaxial connectors are
important, as they provide impedance
matching between the transceiver and
the antenna. For UHF, premium qual-
ity connectors must be used to minimise losses.
Transceivers installed in motor vehicles require careful mounting and
connection. Care must be taken to
ensure that the transceiver is mounted
securely, so that if an accident occurs,
it remains mounted on the dashboard,
where it cannot harm the occupants.
Power connections should be made
directly to the car battery, eliminating
the possibility of vehicle accessory
noise being fed to the transceiver.
All CB transceivers sold these days
are negative earth, allowing the chassis to be directly connected to the
vehicle body. The suppression of ignition interference is of great importance to 27MHz users, who do not
have the benefit of the intrinsic noise
immunity afforded by FM.
Ignition noise can either be radi-
The "Sea Simba" is a 27MHz CB radio
specifically designed for marine
work. It has 10 channels, 5W output
power, a loudhailer/PA, automatic
noise limiting, and adjustable RF &
mic. gain. (Hatadi Electronics).
Designed for the serious operator, the
Pearce-Simpson Super Cheetah MkIII
boasts an in-built scanner, 40-channel
AM/SSB operation & a noise blanker.
It's sold by Jaycar Electronics.
ated or conducted into a CB transceiver. The use of suppression spark
plug leads, grounding the end of the
vehicle exhaust system (which can
act as an antenna, hung under the
body of a car by rubber bands) and
earthing the bonnet by bonding the
hinges using copper braid, will generally eliminate radiated ignition noise.
Direct connection to the vehicle battery is the best method to eliminate
conducted noise.
Licensing
One license per transceiver is required for the operation or possession
of a CB transceiver. Licenses are easily obtained from the Department of
Transport and Communications by
filling in the appropriate form (DOC5 7A) and payment of the appropriate
fee. DOTAC will then issue a callsign
and an operating guide.
CB operation is permitted on a non
interfering basis. This means that if
interference is generated by a CB operator, DOTAC can request the operator to minimise interference by restricting operations until the technical reason for the interference can be
determined and a cure implemented.
In some states of Australia, it is an
offence for drivers to use radio communications equipment while driving. Finally, all equipment must be
type approved, in the case of 27MHz
equipment to DOTAC specification
ECR312 and for UHF, ECR250. As unapproved CB transceivers are prohibited imports, virtually none appear
for sale on the Australian market.
CB etiquette
As any shortwave listener knows,
CB and amateur operators have developed a "language" of their own.
Table 3 shows what are called "10codes" and "Q" codes. The idea of
using these codes was originally as an
aid to communications in poor conditions. These days they are used more
as jargon.
As the CB bands can be shared by
everyone, certain band plans have
been devised to ensure that, for instance, SSB does not interfere with
AM stations and so on. Basically, the
27MHz plan, part of which is law,
states that only AM can be used from
channels 1-14 and that SSB can only
be used from channels 15-40. Also,
certain channels have been dedicated
for specific uses as follows:
Table 2: UHF CB Channels
Channel
Frequency
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
476.425
476.450
476.475
476.500
476.525
476.550
476.575
476.600
476.625
476.650
476.675
476.700
476.725
476.750
476.775
476.800
476.825
476.850
476.875
476.900
476.925
476.950
476.975
477.000
477.025
477.050
477.075
477.100
477.125
477.150
477.175
477.200
477.225
477.250
477.275
477.300
477.325
477.350
477.375
477.400
34
35
36
37
38
39
40
Use
Emergency
Call channel
Emergency
Road channel
Channel 8: AM only. This is the highway channel. It is used by truck drivers, travellers and base stations along
main rqads to pass information relating to traffic conditions.
Channel 9: AM only. This is used as
the emergency channel and is monitored by rescue and volunteer groups
around Australia, who have fast access to police, fire, ambulance and
emergency services.
Channel 11: AM only. This channel
has been allocated "call channel" staJULY
1992
19
Table 3: The Language Of CB Radio
10.100 - rest stop; often interpreted as rest room stop!
THE COMMON 10-CODF;S
10.1 - poor reception; have difficulty receiving you
10.2 - good reception; receiving you well
10.3 - this channel in use, stop transmitting
10.4 - acknowledgement; message received
10.5 - relay message
10.6 - I'm busy
10.7 - closing down (usually temporary close down)
10.8 - back on after closing down
10.9 - repeat what you just said, repeat last over
10.1 O - ready now, was busy
10.13 - please advise weather, road conditions
10.18 - anything for me?
10.20 - location (same as 0TH); often used as "hometwenty" or just "twenty"
10.21 - call by telephone
10.23 - standby (same as ORX)
10.27 - I am moving to channel. ..
10.28 - identify; what is your callsign (same as ORZ)?
10.32 - signal check; usually used to give signal reports
10.33 - emergency traffic at this station
10.34 - in trouble, need help
10.36 - correct time (you never get it!)
10.41 - go to channel ... (same as OSY to .. .)
10.44 - I have a message for ...
10.50 - break channel
10.77 - no contact, not receiving you, negative contact
Looking for an economy handheld
model? This unit from Dick Smith
Electronics sells for around $100 &
comes fitted for 1-channel operation.
20
SILICON CHIP
10.200 - police needed at...
THE COMMON 'Q' CODES
ORA - name or handle (what is your name; my name is ...)
ORB - how far away are you?
ORG - what channel am I on?
ORL - busy (I am busy; are you busy... )
ORM - interference; generally from other stations
ORN - natural or noise interference; static, car ignition etc
ORP - low power (applies to those who have a high
power/low power switch)
ORT - going off the air; to stop transmitting
ORU - nothing for you (or have you anything for me?)
ORV - ready? - I'm ready!
ORX - standby
ORZ - what's your callsign? or who's calling?
OSA - signal report (5 by 9, or 4 by 5 or whatever)
OSB - fading or "flutter' on signal
OSL - acknowledgement; same as "ten-four" and "roger".
Used to affirm receipt of message or information.
Hence, OSL cards
OSO - contact
OSP - to relay a message
OSY - change channels or frequency
0TH - location (same as 10-20)
OTR - correct time is ...
tus and is used to establish initial
contact. Once contact is established,
operators are required to move to another channel to continue their conversation.
Channel 16: LSB (lower sideband).
This channel has been designated the
"SSB call channel". Only LSB is used
and once contact has been established,
operators must move to another channel.
Channel 35: LSB. Secondary SSB call
channel, particularly for stations desiring long distance "DX" contacts.
UHF operators have also dedicated
specific channels for certain usage:
Channel 5: UHF emergency channel.
In mos.t capital cities, a repeater operates on this frequency (channel 5 receive, channel 35 transmit) to provide greater coverage of emergency
services.
Channel 11: UHF call channel.
Channel 35: Secondary emergency
channel. As well as being the input
frequency for emergency repeaters, it
can also be used for simplex emergency communications.
Channel 40: UHF highway channel.
In addition, UHF repeaters operate
from channels 1-8 and 31-38 and can
only be accessed using the duplex
mode on UHF CB transceivers. As
each channel is separated by 25kHz,
this 30 channel "split", when using
the repeater mode, equates to a fre quency difference of 750kHz.
Good operating practice dictates
that repeater users keep transmissions
short. In fact, all UHF CB repeaters
are fitted with a time-out function,
which automatically switches the repeater transmitter off if the input signal is held up for too long. It is also
good etiquette to always wait a few
seconds after the audible repeater
"tail" drops out before re-transmitting through a repeater.
This gives other stations the opportunityto "break in", before they travel
outside the range of the repeater. It is
wise to check the input channel of the
repeater during a conversation, just
in case the other station can be heard
at good signal strength. If this is the
case, the stations should move to a
simplex channel to leave the repeater
free for others.
SC
|
