VHF/UHF

APRS

AF5NP APRS, Emergency Communications (EmComm), FM (Frequency Modulation), GPS (Global Positioning System), Packet, Position, VHF/UHF

You may have read or heard the term APRS.  This four letter acronym isn’t self-explanatory but is popular and important enough that we should cover the basics.

Do you need APRS? Unlikely.  Do you want it? Maybe.   Planning to buy a new VHF/UHF radio and wonder if this is a feature worth paying for?  Read on.  APRS is a big topic with way more detail than we can present here so we’ll give you a general idea of what it involves along with some research links to answer these questions yourself.

For starters, APRS stands for Automatic Packet Reporting System.

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Some publications mistakenly call it Automatic Position Reporting System

Refer to our packet topic for a background on what packet radio is all about.  What makes APRS a specialized form of packet is what info is transmitted.

APRS supports four data types, including Position/objects, Status, Messages and Queries.  The position packets contain latitude and longitude, a symbol to be displayed on a map, plus optional fields for altitude, course, speed, radiated power, antenna height above average terrain, antenna gain, and voice operating frequency.

While APRS can send packets over greater distances on HF bands, it is more commonly used with VHF FM (2m) radios to share data of interest in the local area such as GPS coordinates, weather, alerts, announcements, and such.

APRS info and messages can be directly between hams but more commonly, packet data is collected by local repeaters (gateways) and sent to the APRS Internet System (APRS-IS) for retrieval anywhere by anybody with a web browser.  Meaning your unlicensed spouse can see where you are located (technically, your transceiver) at any given time.  It is not a one-way system; APRS both transmits and receives packet data.

Also unlike normal packet radio, APRS blindly sends out data addressed to no one in particular (unconnected). Two things to know about this system: 1) no error correction (clean, strong signals required), 2) someone or something must be monitoring to be useful (another APRS ham or internet gateway).

In addition to several good references below, an excellent resource worth reading right now: Intro to APRS (PDF file link), a presentation prepared by John Gorkos AB0OO of the Joplin (MO) ARC.   It discusses what the system is not, significant info you can get through it, what you can do with it (note two separate sections for this), and suggests next steps for getting involved with APRS.

Given all the possibilities above, the primary use of APRS in ham radio is to have a transmitter location reported to a central database periodically so that others can see where a mobile/portable ham is located.

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This makes APRS particularly useful for public service events and emergency communication (EmComm) situations where managers can easily track mobile resources who have messaging capabilities.

There are numerous web services for viewing APRS maps and data but the main one (and simplest) is  aprs.fi .  Click there and you will be taken to a local map showing locations of ham APRS transmitters in your own area.  Looks like this example:

APRS Map

In North America all APRS data is transmitted on 144.390 MHz.

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Just tune your VHF radio to your global frequency to hear the packet squeal, if you are wondering what it sounds like.

APRS requires not only a 2m FM transceiver but also a computer with display and TNC radio-computer interface, plus (normally) a GPS receiver.  Radios with APRS features built in cost more than ordinary mobile or handheld transceivers, mainly because Continue reading →

Voice Modulation- SSB

AF5NP AM (Amplitude Modulation), Bandwidth, FM (Frequency Modulation), HF (High Frequency), Modulation, SSB (Single Sideband), VHF/UHF

In the last post we explored voice modulation and learned that AM and FM are the two primary modes.  We also noted that single sideband (SSB), a variant of AM, is the dominant form of voice communication on the ham bands below 50 MHz.   This post will delve into the details of SSB.

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SSB is important because it significantly improves the plain AM signal in both efficiency and bandwidth.

G2A06-2019In context of voice modulation, bandwidth means the range of frequencies the signal occupies.  In general, wider bandwidth means higher audio quality but less efficiency, and vice versa.

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The SSB signal is generated using AM but before it is transmitted the carrier and one sideband are removed.  A diagram of an AM signal helps visualize how it starts:

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SSB transmission reduces the power required (more efficient) and occupies a smaller slice of the RF spectrum (narrower bandwidth, ~3kHz), when compared to AM.

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The transmitter circuitry is essentially AM but adds carrier and sideband filters at nominal cost.  The SSB receiver is more complex and expensive than AM because it must reconstruct the missing (mirror image) sideband to create a full voice signal, as well as replace the carrier with a local signal.

Because it has to recover the opposite sideband the SSB receiver is somewhat sensitive to tuning to make the voice sound normal or natural.  You will find that voices sound quite different in clarity and pitch when tuning around the transmit frequency.   A common reaction to hearing off-tune SSB is that it sounds like a quacking duck.  A great video demonstrating some of the nuances of SSB sound and tuning can be found in the links at the bottom.

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So SSB transmits only one sideband, but which one, you ask?  The answer is either.  When the upper sideband is transmitted and received, the operation is called upper sideband (USB).

USB waveform

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Conversely, when the lower sideband is used, the operation is called lower sideband (LSB).

LSB waveform

G2A02-2019In ham radio either one is legal to use in the phone portion of the band plan but by convention LSB is used below 10MHz, and USB is used above 10MHz (note that Continue reading →

Why Hams Care About the Ionosphere

AF5NP Distance, DX, HF (High Frequency), Ionosphere, LUF, MUF, NVIS, Propagation, Skip, Solar, Sun, VHF/UHF

There are many questions concerning the ionosphere and its layers in US license exams.

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Experienced hams talk about the ionosphere a lot these days and we see plenty written on the topic in amateur radio websites and magazines.  So what’s the importance of the ionosphere?

The real magic in ham radio is skywave propagation where signals can travel well beyond line of sight, even to the other side of the planet if conditions are right.  We can have two-way radio communication between Iceland and Australia and places in between because voice, video and data signals may be bent back to earth by the ionosphere.

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The ionosphere is shell of electrons and electrically charged atoms and molecules (ions) that surrounds the Earth, stretching from a height of about 50 km (31 mi) to more than 1,000 km (620 mi).  Because this band is electrically active the ionosphere is able to reflect or refract electromagnetic radiation at certain frequencies, the HF bands in particular.  For most hams communicating beyond line of sight is a big deal and the ionosphere is what makes long distance (DX) contacts commonplace.

Ionosphere bending

There are two defined ionospheric layers at night and four in daytime, the difference being exposure to the sun which provides most of the energy to the ionosphere.

Ionosphere_Layers

In daylight the F layer separates into F1 and F2 regions.  Because F2 is farthest from the earth’s surface it can bend radio waves the greatest distance.

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Long-distance propagation changes with day/night cycles and seasonal variance away from the equator.  There are numerous anomalies and disturbances that can affect the ionosphere.  Between all these factors the ionosphere is not a uniform shell; it has varying height, thickness, and density.  This continually changing area makes HF propagation highly variable.

Also known as skip, ionospheric propagation of shortwave (HF) radio signals travel a specific radius or skip distance from the transmitting antenna.  This makes received signals particularly strong at the skip distance.

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In addition to single skip distance, the earth itself can reflect/refract signals from the ionosphere back up, resulting in a secondary skip or hop and perhaps Continue reading →

Ham Radio Bands

AF5NP Band(s), HF (High Frequency), RF, VHF/UHF, Wavelength

The term band is thrown around constantly in ham radio discussion and it is included in  many questions in US license exam pools.  So what exactly is a radio band?

Parts of the radio frequency spectrum allocated for a common purpose are called a band.  Besides amateur radio, the reader may be familiar with USA commercial broadcast ranges known as AM band and the FM band, or another personal communication chunk of frequencies called the citizens band (CB).

With amateur radio, bands are generally associated with a number (2m or 40m, for example).  This number is approximately equal to the wavelength of that span of frequencies

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We say approximately because a specific wavelength is only valid at one exact frequency and that may be outside the actual range of the band.

Shown below is a chart of the current US amateur bands (dated 2017):

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These 18 bands are are named by their approximate wavelength.  For those who care about such details, the named wavelength (λ) may not actually be inside the designated frequency range.  A table of these is given below:

band wavelengths

Some do, but why don’t all the meter bands line up with wavelengths inside the band?

Lots of discussion on this issue can be found on the internet and two particularly good links are given in the first two references below.  It’s a real combination of history, simplicity, misuse, and existing broadcast band names.

0.7m is the same as 700mm or 70cm; the 70cm name is more commonly used 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

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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 →

Radio Frequency (RF)

AF5NP HF (High Frequency), RF, VHF/UHF

Radio signals are sent via radio waves, which are a form of electromagnetic energy or radiation. T3A07-2018

Recall that a radio wave consists of both electric and magnetic fields oscillating at right angles to each other.EM Fields.png

 

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Combining electrical and magnetic gives us the term electromagnetic.

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Like all waves, radio waves vibrate or oscillate at a specific rate or frequency.

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ewaves.gifThis vibration frequency is normally measured in cycles per second and its units are Hertz.  T5C05-2018.pngRates of oscillation in radio work are thousands and millions of Hertz (Hz).  With standardized metric prefixes for SI units , this means practical radio frequencies are in kHz, MHz, and GHz.

The common and familiar term RF is short for radio frequency.  It’s really an adjective, not a noun.  While we may say just RF (“You have a big RF leak, there, Fred”), we really mean radio frequency energy or signals.  RF is not a thing in and of itself.

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So what is a radio frequency , then?  They are a large chunk of frequencies in the middle of the electromagnetic spectrum (the range of possible frequencies from 0 to measurably high).  Technically radio frequencies start at low audio frequencies and run up to just below infrared light, basically 30Hz-300GHz.  Different sources specify other upper/lower boundaries because a more practical range is the low frequency band up through microwaves.  However you define it, this range of frequencies is  known as the radio spectrum.

RF Spectrum.gif

While hams can use very low frequencies on one end and go up to microwave frequencies at the high end, the more common radio amateur frequencies are in the shortwave, VHF, and UHF range.

We will follow up with detailed posts on the important topics of RF wavelength and amateur radio bands, along with RF safety.  Coming soon to Newhams.info; stay tuned.

 

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?)

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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 →