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Transcript of Session 4 Operating a Ham Station - Rice UniversityPHYS 401 Physics of Ham Radio 86 Session 4...
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PHYS 401 Physics of Ham Radio 86
Session 4 Operating a Ham Station
Chapter 5 Transmitters and Receivers
Antennas & Feedlines
Figures in this course book are reproduced with the permission of the American Radio Relay League.
This booklet was compiled by John P. Cross AB5OX
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PHYS 401 Physics of Ham Radio 87
Typical Amateur Station Layout
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PHYS 401 Physics of Ham Radio 88
Typical Amateur Packet Station
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PHYS 401 Physics of Ham Radio 89
CW Transmitters are the Simplest
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PHYS 401 Physics of Ham Radio 90
Block Diagram of FM Transmitter
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PHYS 401 Physics of Ham Radio 91
Schematic of FM transmitter
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PHYS 401 Physics of Ham Radio 92
Receivers • Radio receivers demodulate the signal - they
retrieve the information from the RF wave. • Receivers convert radio signals into audio
signals. • The heart of the receiver is the detector. • Modern receivers are very sensitive and
very complex - use feedback to increase signal strength
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PHYS 401 Physics of Ham Radio 93
Simple AM Crystal Set
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PHYS 401 Physics of Ham Radio 94
Superheterodyne Receiver
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PHYS 401 Physics of Ham Radio 95
Low Pass Filter
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PHYS 401 Physics of Ham Radio 96
High Pass Filter
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PHYS 401 Physics of Ham Radio 97
Band Pass Filter = low + high in series
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PHYS 401 Physics of Ham Radio 98
CW Receiver
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PHYS 401 Physics of Ham Radio 99
AM Receiver
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PHYS 401 Physics of Ham Radio 100
FM Receiver
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PHYS 401 Physics of Ham Radio 101
Data Modes
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PHYS 401 Physics of Ham Radio 102
Use of Phonetic Alphabet Improves Understanding
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PHYS 401 Physics of Ham Radio 103
Antennas & Feed lines
(Chapter 4)
Figures in this course book are reproduced with the permission of the American Radio Relay League.
This booklet was compiled by John P. Cross AB5OX
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PHYS 401 Physics of Ham Radio 104
Antennas - General Information
• We convert electrical current into radio waves with an antenna.
• The purpose of the antenna is to radiate the energy, propagate the radio wave.
• When receiving, the antenna converts a radio wave into an electrical current.
• A good antenna is worth more than a big amplifier! • It pays also to have good, clean connections to
prevent power losses.
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PHYS 401 Physics of Ham Radio 105
Transmission or Feed Lines
• Special cables or wires that connect the transceiver to the antenna.
• Feed lines, like antennas, have a characteristic impedance which needs to be matched to the transceiver and antenna.
• Matching devices are used to adapt one impedance to another.
• Coaxial cable and parallel conductor (twin lead) are the two most common feed lines.
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PHYS 401 Physics of Ham Radio 106
Coaxial Cable • Impedance 50 Ω: RG-58, RG-8
RG-213 • Impedance 72 Ω: RG-59 RG-11 • Thick cable (RG-8, RG-11) and
good shielding reduces losses. • Advantages are:
– weather resistance – it can be buried – it can be bent or coiled – it can be next to metal – impedance matches most
antennas. • Disadvantage is cost.
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PHYS 401 Physics of Ham Radio 107
Twin Lead (ladder line) • Impedance is 300-450 Ω • Major advantage is low losses
(can have a long run). • Disadvantages are:
– cannot be coiled. – cannot be run near metal. – impedance doesn’t match
modern transmitters. – Limited to less than 30 MHz
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PHYS 401 Physics of Ham Radio 108
Cable Attenuation
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PHYS 401 Physics of Ham Radio 109
Connectors are Important • BNC connectors are compact, often used for hand held
radios – designed for use with RG-58 – low loss, quick connect.
• PL-259/SO-259 commonly used for HF and VHF applications. • N-Type, designed for RG-213 and RG-8,
– low loss – used for UHF applications
• Good soldering technique and careful construction are critical to making good connections of cable to connectors. If solder joint is dull, not a good connection (“cold solder”) Best if it’s shiny
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PHYS 401 Physics of Ham Radio 110
Impedance Matching • Devices are networks of capacitors and inductors. • Transmatch is a device that has adjustable
characteristics so it can be used on several bands. • SWR (standing wave ratio) meter is used to
measure impedance matching. It is connected between the transmitter and the transmatch.
• A balun (balanced to unbalanced) is a device to couple a balanced load to an unbalanced load.
• Balanced: e.g.twin lead, dipoles, neither side to ground.
• Unbalanced: e.g.coax and verticals, one side to ground.
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PHYS 401 Physics of Ham Radio 111
Impedance Matching Hookup
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PHYS 401 Physics of Ham Radio 112
Standing Wave Ratio (SWR) • Ideally, all the forward power from the
transmitter should be emitted by the antenna, if the impedances are matched.
• We want all the forward power to radiate from the antenna and none of it to be reflected.
• SWR is the ratio of the maximum voltage on the line to the minimum, ideally, 1:1.
• SWR of less than 2 is acceptable. Higher than 4 indicates a problem.
• Modern transmitters are designed to match a 52 Ω load. Will shut down power if SWR > 2
• Good matching improves performance!
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PHYS 401 Physics of Ham Radio 113
SWR Meters • Used to measure impedance matching of transmitter
and feed line and the resonant frequency of an antenna.
• Need to determine frequencies the meter was designed for. Outside that range they will not be accurate.
• Problems with antennas can be found with the SWR meter: – erratic measurements could indicate loose connections. – extremely high could indicate shorts or gross dimension
problems – change with time (months) could indicate corrosion.
• Tuning an antenna is probably the most common use.
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PHYS 401 Physics of Ham Radio 114
Half-Wave Dipole Antenna
• The length of the half-wave dipole is calculated by: 1/2λ(ft)=468/f(MHz) 1/4λ(ft)=234/f(MHz)
• This is only accurate for frequencies up to 30 MHz (10 meters)
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PHYS 401 Physics of Ham Radio 115
Dipole Stuff • Insulators are needed for the center and the ends. Can be
bought (cheap) or can be home-brewed from plastic. • Wire choice is important. Best is copper clad steel. 12-14
gauge is suitable. Small gauge wire will will stretch. • Cut wires a little longer than calculated to allow for
connections and to allow fine tuning. • Use good coax with >95% shielding. RG-58 works just fine
for runs up to about 100 feet. • Dipoles radiate most perpendicular to the wire. Alignment
may be important. • Get it as high as you can. Preferable 1/2λ above ground. • Inverted V and slopers work just fine.
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PHYS 401 Physics of Ham Radio 116
More Dipole Stuff • Use your imagination to get lines into trees. Bow
and arrow, rocks and slingshots work well. Send up a light line, then pull through the support ropes.
• Don’t use polypropylene line; it deteriorates. Nylon is better, and dacron is best.
• If you can, support the middle as well as the ends, it makes for a sturdier installation.
• Make sure your antenna is a long way from metal things, flag poles, gutters, etc.
• NEVER NEVER put your antenna near power lines.
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PHYS 401 Physics of Ham Radio 117
Tuning with an SWR Meter • Install SWR meter
at antenna feed point.
• Set transmitter to low power.
• Adjust meter and take series of measurements across frequency band.
• A “dip” indicates the resonant frequency (lowest is best!).
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PHYS 401 Physics of Ham Radio 118
More Tuning With a SWR • If there is no dip, you
must look at the slope of the SWR curve. It slopes down toward the resonant frequency.
• If the minimum is at the low frequency end, the antenna is too long.
• If the minimum is at the high frequency end, the antenna is too short (so make them a little long to start!!)
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PHYS 401 Physics of Ham Radio 119
Multi-Band Dipoles • A simple three band dipole can
be built from ladder line in a manner similar the the simple dipole.
• Advantage is that a single antenna can be used on several bands.
• You will need a transmatch. • Be careful, this kind of antenna
can radiate on several wavelengths. Be sure your transmitter is properly adjusted.
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PHYS 401 Physics of Ham Radio 120
Quarter-Wave Vertical • This is an unbalanced antenna, one
side is grounded. • Omni-directional that tends to
shoot signals toward horizon. • Radiator is 1/4λ = 234/f(MHz). • This is accurate for < 30MHz, end
effects and radiator diameter to frequency ratio make it overestimate for higher frequencies
• Connect center conductor to radiator and shield to ground.
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PHYS 401 Physics of Ham Radio 121
Ground Plane Antenna Easy to build, good outdoors (and indoors)
Gives an “effective” ground not at true ground
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PHYS 401 Physics of Ham Radio 122
Beam Antennas • Directional antennas which provide a lot of gain in the
direction pointed. Beam in direction of shortest piece! • The more elements, the bigger front to back power ratio • Driven element is 1/2 λ, making it impractical for 80 and 40
meters.
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PHYS 401 Physics of Ham Radio 123
Antenna Polarization
• Polarization: Direction of the electric force lines in a radio wave
• Vertical antennas are vertically polarized
• Dipoles are horizontally polarized.
• Best results are obtained with transmitting and receiving antennas having same polarization.
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PHYS 401 Physics of Ham Radio 124
Cubical Quad and Delta Loop
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PHYS 401 Physics of Ham Radio 125
Other Antennas • Handy Talkies often use a “rubber duck.” This
design is compact, but a compromise design. Lower performance (lots shorter than 1/4 λ)
• Better performance can be had with 1/4 and 5/8 λ telescoping antennas.
• Roof mounted 5/8 λ antenna has better gain than the others. Car roof is a great ground plane!
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PHYS 401 Physics of Ham Radio 126
Repeater Overview • Simplex operation- two stations are talking directly on the same
frequency. (standards are 146.52 (2m) and 446.000 (70cm) • Duplex operation - two stations communicating transmitting and
receiving on different frequencies. • Repeater operations - use standard frequency offsets from the
receiving mode. This is automated in most VHF and UHF equipment.
• There is a listing of all amateur repeaters which can be used to find useful frequencies. Many repeaters have special features.
• Repeater frequencies are mostly coordinated to minimize overlap and possible interference.
• Most repeaters are “open”, anyone can use them. • Often incorporate CTCSS or PL tones to avoid interference. If
you don’t have the right tone set, you can hear them but they can’t hear you. Check a repeater directory.
• Setting “memories” on your rig has it remember the proper tones!
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PHYS 401 Physics of Ham Radio 127
Repeater Operations • Don’t call CQ on a repeater, simply say: “AB5OX
listening” • Turn down your squelch then back up to just cover
the noise level. (be sure noone else is talking!) • To join a conversation simply say your call sign
during a break and wait to be acknowledged. • “Break” means that you have emergency traffic,
don’t use it unless you need it. • Most repeaters have a courtesy beep which
indicates that the transmitting station has released the PTT.
• Most repeaters also have a time out feature to protect the transmitter.
• Be Courteous, it’s more fun that way.
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PHYS 401 Physics of Ham Radio 128
CW (Morse Code) Operations • Listen before transmitting “QRL?” • Send at a speed that you can easily read. • Calling CQ, use the “3 X 3” call:
– CQ CQ CQ DE AB5OX AB5OX AB5OX K • To answer, use “2 X 2” format:
– AB5OX AB5OX DE K5CXH K5CXH AR • Use appropriate prosigns, Q signals and abbreviations:
– K5CXH DE AB5OX BT TNX FOR CALL BT UR RST 559 BT NAME JOHN QTH CAMP STRAKE NR HOUSTON BK
• Close the conversation as follows: – TNX QSO ES 73 BT CUAGN K5CXH DE AB5OX SK (Use similar prosigns for PSK31)
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PHYS 401 Physics of Ham Radio 129
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PHYS 401 Physics of Ham Radio 130
Common Prosigns
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PHYS 401 Physics of Ham Radio 131
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PHYS 401 Physics of Ham Radio 132
Single Sideband (SSB) Operations • Voice communications are known as “phone”: SSB, AM, FM.
• SSB is the most common phone mode on HF. • Initiate a contact with “3 X 3” call as with CW, but use phonetics for your call sign.
• Reply with the calling station’s call sign, this is , then your call phonetically.
• Keep your conversation plain and simple. Be courteous. • Don’t use prosigns or Q signals and don’t use CB jargon.
• Signal reports are only “RS”. • Listen before you talk, use VOX or PTT and listen to make sure you are not doubling.
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PHYS 401 Physics of Ham Radio 133
Data Emissions - RTTY • RTTY - Radio Teletype , narrow band direct printing
telegraphy - continuous signal modulated between two frequencies. – FSK - frequency shift keying - CW carrier shifted 170Hz
(HF) – ASFK - audio-frequency shift keying - shifting audio tone
transmitted by FM (VHF). MCW (modified CW). • Only 1 QSO can be maintained on a given frequency
and it requires operator control of transmissions. • Modern systems use computers and modems. • Baud rates are typically 300 (HF) and up to 1200
(VHF). • Call CQ with the “3-6 X 3” method. • Use prosigns and Q signals.
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PHYS 401 Physics of Ham Radio 134
Data Emissions – PSK-31 • Allows conversations with more background noise
than a voice conversation (will get through when Phone won’t). Always uses UPPER sideband (USB)
• Several conversations on one frequency, just using different frequency tones. See where everyone is using the “waterfall”.
• System is controlled with a computer using its sound card to interpret and send. Special software, generally free or cheap.
• PSK means “phase shift keying” to key the 0’s and 1’s. “31” means 31 baud (slow but efficient for HF)
• Standard frequencies: – 7.017.15 40m – 14.070 (14.035 at night) 20m – 28.120 10m
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PHYS 401 Physics of Ham Radio 135
Sending photos and video • Video (Slow Scan TV) takes a higher frequency so
can send data at a faster rate. • Scans the picture across, one horizontal line at a
time. First was only 128 lines but now also you can get 256.
• System is controlled with a computer and special software.
• Tone coding. “tee-del-ee” • Standard frequencies:
– 3.845 80m – 7.170 40m – 14.230 20m – 28.680 10m