session 4 operating a ham station - rice universityphys 401 physics of ham radio 86 session 4...

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


Typical Amateur Station Layout


Typical Amateur Packet Station


CW Transmitters are the Simplest


Block Diagram of FM Transmitter


Schematic of FM transmitter


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


Simple AM Crystal Set


Superheterodyne Receiver


Low Pass Filter


High Pass Filter


Band Pass Filter = low + high in series


CW Receiver


AM Receiver


FM Receiver


Data Modes


Use of Phonetic Alphabet Improves Understanding


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


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.


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.


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.


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


Cable Attenuation


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


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.


Impedance Matching Hookup


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!


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.


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)


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.


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.


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!).


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!!)


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.


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.


Ground Plane Antenna Easy to build, good outdoors (and indoors)

Gives an “effective” ground not at true ground


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.


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.


Cubical Quad and Delta Loop


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!


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!


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.


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)


Common Prosigns


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.


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.


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


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

session 4 operating a ham station - rice universityphys 401 physics of ham radio 86 session 4...

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