Antenna

Coaxial Cable (Coax)

AF5NP Antenna, Attenuation, Cable, Coax (ial Cable), Impedance, Loss

Because it’s commonly used in radio work, every ham should be familiar with coaxial cable, often simply called coax.

Coaxial cable is most often used between the transceiver (or T/R switch) and antenna.  In this application coax acts as the feed line (AKA transmission line) to carry transmitted and received RF signals between the antenna and radio.  Other types of feed line can be employed but coax is used by many hams because it is easy to work with and readily available.

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Coax  is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Most coaxial cables also have an insulating outer sheath or jacket.  The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis.

300px-Coaxial_cable_cutaway.svg

To be useful coaxial cable must be terminated with mating RF connectors.  An experienced ham may terminate their own coax; at greater cost they may purchase ready-made and tested assemblies.

coax ca assy  coax ca assy2

A wide variety of coaxial cable and assemblies are available with different characteristics. A quick summary of the important features:

  • Characteristic impedance
  • Signal loss
  • Power capacity
  • Diameter/weight
  • Flexibility
  • Environmental resistance

A seventh important characteristic of coax is velocity factor but that is a more advanced topic of lesser importance so we’ll simply mention it here.

Coaxial cable selection for each installation may be a compromise between features, requirements, and cost. The ham has to factor in what he needs or wants, what is available, and what it costs.

A quick look at these features of coaxial cable: Continue reading →

SWR

AF5NP Analyzer, Antenna, Impedance, Standing Waves, SWR (Standing Wave Ratio)

The standing wave ratio (SWR) is an important topic to hams regardless if they are working HF, VHF, UHF or any other frequency range allocated to radio amateurs.  Unfortunately it is technically involved and somewhat complex so is not intuitive or easy for non-technical folks to understand.  We’ll give a simplified explanation of SWR here and give you a basic idea of its significance and how hams relate to it.

The simplest way to think of SWR is as a measure of impedance matching.  Most commonly it is looking at the impedance differences between transceiver, transmission line (more often coaxial cable), and antenna.

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Assuming that all modern radios and cable have 50Ω impedance, the real SWR of interest boils down to the match between the transmission line and antenna.

As we mentioned in a previous post, when impedance of a source equals load impedance the best possible signal coupling occurs. Conversely, when impedances are not the same, signals couple poorly.  This is true of all electronics circuitry involving AC waveforms.

In amateur radio SWR focus is on transceiver to antenna coupling where we want to maximize RF power transfer in both transmit and receive modes.  When impedances do not match, received signals will be weak or non-existent; when transmitting, power will not radiate well from the antenna.  The ideal or “perfect” SWR for best possible transmit/receive coupling is 1:1, meaning a 50Ω radio/transmission line to a 50Ω antenna.

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SWR is simply the ratio of two impedances being measured.  It is commonly expressed in the X:X format and the larger value is always given first, regardless of which side is higher.

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With a 50Ω radio and 50Ω coax cable, a 4:1 SWR could indicate either a 12.5Ω or a 200Ω load (antenna).  Similar examples for 50Ω cable are contained in the General class exam pool:

G9A09-2015G9A10-2015A ham’s main concern with high SWR is significant power reflected back from the load, which stresses the transmitter power amplifier.  While a 1:1 SWR is ideal, practically speaking, 1.5:1 or less is good.  Many modern transceivers automatically reduce transmit power with a SWR greater than 2:1.

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SWR can be measured Continue reading →

HT Antenna Improvement

AF5NP Antenna, Counterpoise, HT (Handheld Transceiver), J-Pole, Rat Tail, Slim Jim, VHF/UHF

The handheld transceiver (HT) is likely a new ham’s first radio.  This VHF/UHF rig is relatively inexpensive, compact and fairly useful for local communication via repeater or simplex operation.

Unfortunately, HT  performance is typically limited by its low power and cheap factory antenna.

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There are three easy ways to improve the HT antenna.  These ideas are from our post on Understanding Antennas but we wanted to elaborate a bit on them here.

The first improvement is to get a 2m ¼-wave or 5/8-wave whip antenna.

This 2m ¼-wave whip is much longer (~19″) compared to the factory antenna but gives dramatically better performance (roughly equivalent of 5x power):

QW whip

This telescoping 5/8-wave whip should (in theory) perform better than the ¼-wave monopole (shown with 5/8-wave mobile whip):

5_8 Whip

These two antennas can be purchased new in the $20-30 range; well worth the money.

While the antenna can be improved with a longer whip, vertical monopole performance is also limited by the HT’s indirect ground plane.

The counterpoise that makes the vertical monopole behave like a λ/2 dipole on a HT is the operator’s body.  It is capacitively coupled to the ham’s body through the plastic case and metal shell around the RF circuitry.

This indirect counterpoise coupling is not only weak but also highly variable and unpredictable.

The good news is that we can improve the counterpoise simply by adding a wire to the HT antenna connection.

By connecting a ¼-wave  wire (~19” for 146MHz) to the antenna connector outer terminal, we create a physical counterpoise in place of the indirect ground plane through the operator’s body.

This gives superior performance under difficult conditions and is easy to do.

These physical counterpoise wires are known as rat tails or tiger tails due to their appearance.

Rat tail counterpoise installation is quick and easy.  Simply unscrew the antenna, slip the rat tail over the connector and re-attach the antenna

tiger tail1

tiger tail2

tiger tail3

tiger tail4

The rat tail can simply hang down in a gentle arc where it won’t be much in the way of anything. Even better, you can hold the wire out  in the direction of communication.  Gain/directivity is achieved Continue reading →

Indirect RF Hazards

AF5NP Antenna, Controlled, Duty Cycle, Environment, Evaluation, Exposure, Hazard, HF (High Frequency), Ionizing, Limits, MPE, Protection, Radiation, RF, Safety, SAR, Uncontrolled, VHF/UHF

Part 3 on Safety

Safety is an important topic in ham radio.  There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Part 1 on general electrical hazards and Part 2 on contact RF hazards were posted previously.  This post will address indirect RF hazards.  In case you are not familiar with the specifics of RF energy, refer to our post on the subject.

Here we are concerned about non-contact RF energy.  A long and involved topic (sorry about that) but full of useful detail.

While it involves radiation, RF energy radiates at lower wavelengths where it is least hazardous.

radiation spectrum.JPG

From the electromagnetic spectrum diagram above we see that radio waves are on the low end of energy levels.  As the frequency increases (wavelengths decrease) the energy in electron volts increases exponentially.  Energy above 250eV (or so) is ionizing, which in addition to radiation burns can cause cell damage and mutations, leading to cancer and other maladies, as would radioactive material.

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Fortunately for hams, all radio frequencies are well below the ionizing radiation energy levels.

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Ham radio operators are radio  active, not radioactive. 🙂Amateur radio activeNow just because RF radiation is non-ionizing doesn’t mean it is completely safe.  Besides the direct contact hazard, exposure to radio frequency energy may cause localized tissue heating, particularly in the eyes and male reproductive area (here’s where a lady ham has an advantage, hihi).  Non-thermal effects of RF radiation are being studied constantly because, while compelling, they are somewhat ambiguous and unproven.

Because RF energy has this radiated exposure risk, rules and regulations have arisen to protect people from such hazards.  In the USA this is done at the federal level by both the FCC (radio communications) and OSHA (occupational).  There are also guidelines for RF radiation published by the ARRL and the IEEE.  Internationally, most countries apart from the US have similar guidelines, as does the World Health Organization (WHO).  References to some of these are given at the end of this presentation.

Specific to US radio amateurs, the FCC instituted RF field exposure limits called Maximum Permissible Exposure (MPE). Continue reading →

Going Mobile

AF5NP Amateur Radio, Antenna, Emergency Communications (EmComm), Ham Radio, HT (Handheld Transceiver), Mobile, Transceiver

The Who had a hit tune entitled Going Mobile that may be playing in your head right now.  While the song celebrates the joy of living in a mobile home and traveling caravan-style in the UK, going mobile to hams means using radio equipment in your vehicle.

While some hams have HF radio setups in their cars, mobile predominantly means local VHF/UHF communication.  Besides bring able to talk to our ham buddies while driving around, 2m/70cm capability is particularly useful in case of disaster or other emergency communication (EmComm) situations.  It is perfect for storm spotting and certain public service events.

Mobile operation is popular and important enough that there are a number of US license exam questions involving the topic as you will see below.

Installing and using amateur radio equipment in one’s personal vehicle is too large a topic to cover here so we’ll simply advise you to research details on your own.  Talk to fellow hams and see what/how/why they installed their own gear.

The internet is also a vast resource for [mostly good] info .  One noteworthy site dedicated to mobile ham operation is managed by Alan Applegate, K0BG, and is located here.   It contains exceptionally useful info on most topics presented below.  We encourage you to use this site as a primary reference for your own mobile radio installation and operation.  The ABCs topic is the best place to start.

Before embarking on any of this yourself, there are several important points to consider:

  • Radio type
  • Radio control location
  • Radio mounting
  • Radio power wiring
  • Antenna type and mounting
  • Radio audio/speaker
  • Transmitting while driving
  • Hands-free/Distracted driving laws
  • Noise and interference

We will scratch the surface of each of these topics here:

Radio type-  Choose a mobile radio that best fits your needs, desires, and budget based on several factors:

  • Brand– quality/reliability and/or familiarity/loyalty
  • Transmit power (Watts)
  • Features– Auto power-off, APRS, dual-channel, remote head, cross-band, packet
  • VHF/UHF (V/U) or HF?
  • FM only, or multi-mode?
  • Single-band, dual-band, tri-band, or quad-band?
  • Analog or digital communication, or both?
  • New, reconditioned, or used?

Note that while a hand-held transceiver (HT) can be used in a car, it is significantly limited by its antenna and transmit power.  Both can be improved (linear amplifier and external antenna) but if you really want good mobile performance you should consider a purpose-specific mobile radio.

Radio control location-  Modern mobile transceivers typically feature removable front panels where the operator controls can be positioned in a more convenient, ergonomic, and safe location using a smaller footprint. Continue reading →

Antenna Gain

AF5NP Antenna, dB, Decibel, Dipole, Efficiency, Gain

Newer amateur radio operators may read or hear some discussion of antenna gain.  The gist of it usually involves how much stronger signals are with a particular type of antenna.

This concept of antenna gain can be confusing or misleading to new hams because it sort of suggests that some antennas actually amplify received or transmitted RF signals.  Not so.

Like the decibel (dB), antenna ‘gain’ is always relative.  So when we speak of antenna gain it refers to a performance improvement compared to a different type of antenna.

More commonly, gain is used to compare highly directional antennas (beams, dishes) to monopoles or dipoles.

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While antenna gain usually emphasizes directivity it may also be used to compare two similar types with different characteristics, as efficiency is another contributing factor.  For example, we can observe and measure the relative gain of a stubby “rubber duck” handheld radio antenna (pathetic) vs. a 5/8-wave whip (much better) even though they are both vertical monopoles with the same directivity.

The two types of antennas usually referenced against are isotropic and the simple dipole.  When measuring performance of other antennas, they will often be compared to one of these two.

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If the gain improvement is relative to the theoretical isotropic antenna, the units should specify the gain as dBi.  If measured against a dipole antenna, the gain should indicate dBd.  Any other comparisons should mention the reference antenna in the text.

Some good references for antenna gain are given below: Continue reading →

How Far Can I Communicate?

AF5NP Antenna, Distance, DX, HF (High Frequency), Signal, VHF/UHF

One of the more interesting questions a new or prospective ham will have is, “how far can I communicate?”  The frustrating answer is, “it depends…” (don’t you hate hearing that?)

dx-map

There are many factors involved in the limits to distance of radio communication.  Carrier frequency is the huge one, followed by operating mode, antenna characteristics and transmit power. Time of day, solar activity and the season (spring, summer, autumn, winter) also have a big impact on range.  Natural (thunderstorms, aurora, geologic, cosmic) and man-made (crowded band, power lines, noisy electronics) interference can also limit or disrupt a radio contact.  Also factor in the use of repeaters (terrestrial and space satellites) or reflective objects (structures, moon, meteor showers), plus unusual weather conditions and you have a lot to consider.

Since many hams get started using VHF/UHF radios for local communication, let’s talk about this first.  VHF/UHF radio wave propagation is normally limited to line-of-sight, meaning the antennas at each end must have a clear path between them (no obstructions such as buildings, trees, and particularly, the earth).

3-20 miles is a realistic range for VHF/UHF hand-held radios on the ground, depending mainly on a clear path and relative height of the two parties.  Throw in a repeater with a high antenna and that range extends considerably.  Raising your own antenna up higher Continue reading →

Don’t Settle for Just a HT

AF5NP Amateur Radio, Amplifier, Antenna, HT (Handheld Transceiver), Mic (rophone), Rat Tail, Repeater, VHF/UHF, Yagi

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Often a new ham’s first radio is a handheld transceiver (HT).  A HT represents the lowest-cost entry point to amateur radio and is relatively easy to set up and use.  Your first on-air experience as a licensed ham may involve a HT on a local VHF/UHF repeater, and that’s fine.

But don’t settle for just a HT as supplied by the manufacturer for your early ham radio experience.  You are almost certainly going to be frustrated and disappointed at its performance to the point of giving up on ham radio and wondering why all these hams are so enthusiastic about the hobby.

Don Keith N4KC makes this point eloquently  in his ‘HT Trap’ article where he discusses how easily a new ham can get discouraged with amateur radio because of the limitations of a stock HT.  I have observed this as well while helping new hams get set up in a local EmComm organization.

Huge improvements in HT performance or ease of use can be accomplished with three accessories.

First and foremost is the Continue reading →

Get on the Air Now!

AF5NP Amateur Radio, Antenna, Book, Ham Radio, Ham-Speak, HF (High Frequency), HT (Handheld Transceiver), Recommended Reading, Terminology, Vocabulary

An outstanding resource for amateur radio operators, and new or prospective hams in particular, is a paperback book by Don Keith N4KC entitled, GET ON THE AIR…NOW!

    

There is something for everyone here: Folks who are interested in ham radio, those who just got a license, experienced hams who lose interest, and long-time hams who are looking for something to share with newbies. N4KC covers most of what current and prospective ham radio operators need to know and he does a great job of selling the hobby/interest. And no, he’s not pushing Morse code, although CW operation is one of the more interesting aspects of amateur radio.

The main emphasis of the book is encouraging licensees to actually get on the air and experience real ham radio, not to get frustrated with bad experiences and limited equipment and then give up on our hobby.  He addresses some of the common discouragements and steers us to realistic remedies.  Chapter five is a practical discussion of antennas and I particularly appreciate chapter six with Don’s concise description of what to expect on the HF bands.

gotan TOC

The second half of the book is a comprehensive dictionary of “ham-speak”–amateur radio terms, abbreviations and slang, useful to all hams, new and old.

About $19 with a Kindle version for $9.  Highly recommended and the first item listed on a new site page entitled Recommended Reading.

Practical Skills For the Radio Amateur

AF5NP Antenna, ARRL, DIY, Elmer, Kit, Multimeter, Practical, Skills, Technique

While not every ham is technically inclined or particularly handy, amateur radio operators tend to be do-it-yourself (DIY) kind of people who often build, install, and fix their gear and other things.  In many ways hams are some of the original “Makers” and experimenters who have actually helped further the art and science of radio and communications technology.

To encourage and further this historic reputation, consider developing in yourself some of the practical skills that ham radio operators are stereotyped to possess.  While the list rightly could be more extensive, we will suggest four basic ones here:

  • Electronic soldering
  • Using a multimeter
  • Stripping and terminating different kinds of wire and cable
  • Drilling and cutting material (fabrication)

We can’t go into details on these here, so the reader will need to learn about these skills on their own.  Besides researching them on the web, how can you develop these skills and techniques?  As always, consult your Elmer for some guidance on any or all of these topics.  On your own you can also read up on different subjects in books, magazines and on the internet. The ARRL Handbook has plenty of info on these subjects and is a highly recommended reference.  QST magazine is also a good resource.

Building an electronic kit is a wonderful experience that will teach you a lot about components and soldering.  Local clubs may also host training/practice sessions in some of these areas.  A VHF antenna build is another great way to gain experience with stripping, terminating and soldering and may also involve a multimeter.

Feel free to chime in with your own suggestions for practical skills in the comments below.

Antenna Lightning Protection

AF5NP Antenna, Coax (ial Cable), Feedline, Lightning, Protection

Many hams have a VHF/UHF radio and antenna for local communication, especially if they are involved in EmComm.  Ideally you have an exterior antenna up high for best performance with your radio. The downside to that is that vertically-oriented VHF/UHF  monopole antennas are a juicy target for lightning strikes.  Basically, they look like a lightning rod.

Lightning Antenna

Lightning wants to go to ground and if the best path is through your antenna and feed line, your radio is likely to be destroyed.  And if you’re right near the radio when it happens, you might be injured, or a fire might be started by the lightning strike.  Bottom line, bad things can happen with an outdoor antenna during a thunderstorm.

W0ZUX lightning damage
Lightning damage in W0ZUX shack

Lightning protection is important to have.  There are numerous sources of arresters available, mostly for coaxial cable (feed line).  Some simple and cheap, others complex and costly.  How much is your radio and even your house worth to you?

Here are some commonly available coaxial cable lightning arresters:

Arrestor4     Arrestor3     Arrestor2

Even better than these stand-alone arresters with separate ground wires is to group them on a plate that is well-grounded.

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Special ground rods with arrester mounting plates are available for this:

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Common lightning arresters on your antenna feed line help only with minor stray lightning bolts.  A direct strike on your antenna cannot be stopped by a simple arrester; there is too much energy involved to dissipate.  The radio will be destroyed in such a case, along with possible damage and injury.

So what can you do to protect yourself and your radio from lightning?  In addition to using arresters the best way is to Continue reading →

Keep That HT Antenna Vertical

AF5NP Antenna, HT (Handheld Transceiver), Polarization

The previous post introduced you to the handheld transceiver (HT) and suggested that it had limitations.

One of the HTs weaknesses is that because it is hand held, the operator must maintain the antenna pointing up for maximum performance, as shown below.

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This is because repeater and mobile antennas are always vertically oriented and the handheld antenna should match orientation for maximum power transfer.

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Antennas are polarized according to Continue reading →

The Handheld Transceiver (HT)

AF5NP Antenna, HT (Handheld Transceiver), Repeater

A handheld transceiver (HT) is often a new ham’s first radio.  As the name suggests, it is small enough to hold in your hand and has enough performance to be useful under many circumstances.

zys-ft-60rThe appeal of a HT is in its relatively low cost plus its obvious portability.  Some new hams want to spend as little as possible to get started in amateur radio and new HTs can be had for less than $50 (although not recommended by experienced hams).  Other new hams get started with a local emergency communications group which uses them.  Still others simply want a radio for keeping in touch with others while hiking or some other outdoor activity.

These radios have a practical range of one to three miles from one HT on the ground to another.  This is limited mostly by power and terrain or obstructions.  Greater range is achieved by operating from an elevated position or through the use of repeaters (refer to the repeaters topic).

Amateur use of handhelds is most common on the 2m (146MHz) VHF and 70cm (435MHz) UHF bands using frequency modulation (FM).  HTs are available for a few other VHF and UHF ham bands as well, depending on local usage and repeater support.  While HTs can be found for upper HF bands, antenna length makes them less practical as handheld devices.

Dual-band HTs are quite common and practical, costing little more than a single-band radio.  Many of these also allow the user to receive non-ham band transmissions such as weather alerts, aircraft, and police-fire-EMS dispatching.

While useful in some situations, HTs have limitations for ham radio use.  To obtain reasonable battery life a HT Continue reading →

Understanding Antennas-A Simplified Perspective

AF5NP Antenna, Bandwidth, Counterpoise, Delta, Dipole, Directivity, Efficiency, Gain, Ground Plane, HT (Handheld Transceiver), Impedance, J-Pole, Loop, Magnetic Mount (Mag Mount), Mobile, Monopole, Polarization, Quad, Rat Tail, Resonant, Rubber Duck, Standing Waves, SWR (Standing Wave Ratio), Transmission Line, Wavelength, Yagi

A PowerPoint slideshow, Understanding Antennas / A Simplified Perspective for Ham Radio Operators is downloadable here: Understanding Antennas-A Simplified Perspective

This presentation provides a working understanding of amateur radio antennas without being overly technical or dry.

The target audience is newer hams with limited knowledge of antennas.  It is presented at the Technician license level. You will see Continue reading →