Chapter 25 - ve3bux.com

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Chapter 25: UHV/VHF Operation
Introduction: First Contacts
• For most amateurs, their first solo-contacts
tend to be on 2m or 70cm (VHF/UHF
respectively)
– Recall: 2m = 144-148 MHz & 70cm = 430-450 MHz
– Only basic qualifications required
– Affordable equipment for under $100
– Relatively simple operating procedures
– Offers best introduction to local (established)
amateurs
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VHF/UHF: Basic overview
2M
1.25m
70cm
Frequencies
144-148 MHz
222-225 MHz
430-450 MHz
Band Size
4 MHz
5 MHz
20 MHz
Maximum
Bandwidth
30 kHz (FM-wide)
100kHz
12 MHz (DSS)
Calling
Frequency
144.100 MHz – CW
146.520 MHz – FM
222.1 MHz – CW
222.2 MHz – SSB
432.1 MHz – CW
432.2 MHz – SSB
446.0 MHz – FM
Typical
Repeater
Offset
0.6 MHz
0.6 MHz
5 MHz
Common
Uses
CW, Voice, APRS,
Packet, Satellite (U/L)
CW, Voice, Packet
CW, Voice, Packet,
Satellite (D/L), ATV
Less
Common
Uses
Remote linking,
Moonbounce,
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Operating: Basic Guidelines
• Listen, Listen, Listen!
– No matter what the frequency, ensure that you will not
interrupt a contact in-progress before transmitting
– By listening first, you learn the established etiquette on-air
• Use only the minimum power necessary to conduct a
contact
• When using a “calling frequency” be sure to QSY once
established
– Determine a mutually agreed frequency and move to it to
continue chatting
• Always comply with the Radiocommunication Act
4
QSO: Methods of making a contact
• There are three possible schemes for making a
contact:
– Simplex
– Half-Duplex
– Full-Duplex
• Each method has benefits and drawbacks
– Ease of implementation
– Cost of hardware associated
– Etc..
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Simplex: The most basic QSO
• Any method of communication which uses the
same frequency for transmission and
reception
• Only one person may transmit at a time,
otherwise, you are “doubling” over each other
• Simplest form of communication
• Ex: Walkie-Talkies as a kid
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Duplex: Using different TX/RX Freq.
• Duplex (half and full) is any method of
communication which uses different transmit and
receive frequencies
• Half-duplex:
– As with simplex, only one person may transmit at a
time for effective communication
– Repeaters commonly operate as half-duplex
• Full-duplex:
– Seldom used due to the technical challenges
– Common example is the cellular telephone
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Repeaters: A Primer
• Repeaters are a very popular
resource in amateur radio
• Frequently used by local residents to
improve their “coverage area”
• Many local “nets” are hosted on
repeaters because of their enhanced
coverage area
• May be used to link distant
geographic locations via
– RF
• Eg. VE2REH network in Quebec
– Internet
• IRLP, Echolink
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Repeaters: Major Types
• What:
– Any radio station which automatically retransmits
an input signal to increase the effective range of
the original signal
– Generally placed in a highly favourable location
such as top of a tall building, mountain-top, etc.
Simplex
Half-Duplex
Full-Duplex
Cross-Band
--
HT → Car →
APRS iGate
Satellite
Operation
Same-Band
“Parrot-Box”
Standard
Repeater
WiFi & Digital
“repeaters”
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Repeaters: Privileges
• Basic licensee:
– Use any open repeaters with operating frequencies which are
within the permitted range of the user (ie. your privileges)
• Basic (70% < 80%) can use only those repeaters which operate on: 6m,
VHF, UHF
• Basic+ (≥80%) may use any repeaters, even those which theoretically
retransmit on HF
– Own/operate a cross-band repeater
• In addition to Basic privileges, an Advanced operator may
– Own/operate a same-band repeater
• Repeater is generally given its own callsign and the input/output
frequency pairs are supposed to be managed by a repeater council
• Must conform to all Radiocommunication Act requirements
– Ie. station identification at least every 30 minutes
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Repeaters: How It Works
• Simply take an incoming signal and
retransmit at higher power, generally in the
same band but on a slightly different
frequency (the offset)
– Generally done with two commercial radios
designed for this purpose (100% duty cycle)
• Repeater is generally controlled via DTMF
tones and a controller board
– Handles on/off operation, CTCSS tones,
identification
• When operating in the same band, a cavity
filter (very high Q) is frequently used so that
the same antenna can be used for
simultaneous TX/RX
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Coded Squelch: Preventing Noise
• Sub audible tones used in (RF) noisy
environment to trigger a radio’s squelch only
when a signal with the associated coded
squelch is present
• Two major code types:
– CTCSS
• Continuous Tone-Coded Squelch System
– DCS/DTCS
• Digitally (Tone) Coded Squelch
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CTCSS: Most Common
• As many as 50 sub-audible tones
• Originally only 32 tones, but was adapted to incorporate PL
tones (Motorola)
67.0 Hz
94.8 Hz
131.8 Hz
171.3 Hz
203.5 Hz
69.3 Hz
97.4 Hz
136.5 Hz
173.8 Hz
206.5 Hz
71.9 Hz
100.0 Hz
141.3 Hz
177.3 Hz
210.7 Hz
74.4 Hz
103.5 Hz
146.2 Hz
179.9 Hz
218.1 Hz
77.0 Hz
107.2 Hz
151.4 Hz
183.5 Hz
225.7 Hz
79.7 Hz
110.9 Hz
156.7 Hz
186.2 Hz
229.1 Hz
82.5 Hz
114.8 Hz
159.8 Hz
189.9 Hz
233.6 Hz
85.4 Hz
118.8 Hz
162.2 Hz
192.8 Hz
241.8 Hz
88.5 Hz
123.0 Hz
165.5 Hz
196.6 Hz
250.3 Hz
91.5 Hz
127.3 Hz
167.9 Hz
199.5 Hz
254.1 Hz
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DCS: Seldom Used
• DCS superimposes FSK data (134.4bps) onto
the transmitted signal
• Similar to CTCSS, the DCS data serves to
prevent squelch opening unless the correct
data is received
• Has great potential, however, control boards
are more cumbersome to implement
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Repeaters: How to start
• To use a repeater, you need some information:
– Repeater’s TX & RX frequencies
• Repeaters are listed by the frequency at which they
transmit
• You must determine the repeater’s receive (listening)
frequency by using the offset for the band the repeater
is operating on
– Control tone(s) (if used)
• Often used in radio-congested areas to reduce
unwanted retransmission of garbage
• Generally listed with the repeater’s TX frequency
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Repeaters: Simple Example
• Let’s use VE3TWO as an example. It is listed simply as:
VE3TWO 147.3 MHz (+)
• This is the repeater’s transmit frequency
– Following convention, we know that repeaters which
operate on 2m use 0.6 MHz as the offset value (unless
otherwise stated)
• The (+) means a positive offset frequency for the
repeater’s receive frequency so we add 0.6 MHz to
determine the “listening” frequency
147.3 MHz + 0.6 MHz = 147.9 MHz
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Repeaters: Advanced Example
• Suppose a repeater is listed as:
VE3FAKE
147.65 MHz (-)
(151.4 / 110.9)*
• To use the repeater, set your radio to:
– RX on 147.65 MHz
• using CTCSS tone 151.4 on receive
– TX on 147.05 MHz
• using CTCSS tone 110.9 on transmit
*unless otherwise stated, assume that CTCSS tones are listed as (out/in)
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Repeater Linking: RF
• Repeaters may be linked to each other by an RF link to
increase total coverage area
• When you transmit on repeater A’s input (listen) frequency, all
repeaters (including A) retransmit your signal
147.4 MHz
“Hi Tom..”
“Hi
Tom..”
A’s Incoming 70cm RF link locked out by 2m reception (in use)
Blue = 2m “open repeater” frequency
Red = 70cm “rf link” frequency
you
147.4 MHz(-)
434.80 MHz (+0.6)
“Hi
Tom..”
distant
station
(Tom)
146.3 MHz
147.65 MHz
434.86 MHz
147.65 MHz(-)
434.86 MHz (-0.6)
146.3 MHz(+)
434.86 MHz (-0.6)
“Hi
Tom..”
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Repeater Linking: Internet
• IRLP
– Internet Radio Linking Project
Radio↔ Repeater (A)
147.05 MHz(+)
Node: 2001
Repeater (B) ↔ Radio
Internet
146.7 MHz (-)
Node: 2002
•Using your radio which is set to: (TX 147.65MHz, RX 147.05MHz)
you would link to the distant repeater by pressing: “2002” on the
DTMF keypad while holding the PTT button
•Once the IRLP link is established, you could then transmit to
your local repeater and have the distant repeater (B) retransmit
at 146.7MHz
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Repeater Linking: Echolink
• Echolink is similar to IRLP with the exception
that you can link to distant repeaters directly
from a computer, dropping the radio-torepeater portion of the link
• Theoretically possible to have straight
echolink-to-echolink contacts without even
using a radio
– Not really radio any more, huh?
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