Propagation

Mode Madness

AF5NP CW, Digital, Mode, Modulation, Operation, Phone, Propagation, Satellite, Split

In ham radio the term mode has at least five distinct meanings.  It’s confusing for even experienced hams so we’ll try to tame some of this madness.

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If you’re a new ham with a handheld or mobile transceiver to talk on the local repeater, mode doesn’t mean much to you.  Your basic radio has no mode controls because it can only do one thing.  In this case you are operating in voice mode using frequency modulation (FM).  Guess what?  These are the first two—and most important—of the definitions of mode.  These are operating and modulation modes.

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Below we will explore the five different contexts for mode found in US license exam questions:

  • Operating
  • Modulation
  • Propagation
  • Satellite
  • Split

Operating Mode-  The most basic definition of mode; a general category of radio transmission and reception.  There are three or four operating modes, depending on how they are categorized.  The common three are:

  • CW (continuous wave), typically for Morse code (radiotelegraphy)
  • Radiotelephony (phone), a fancy term for voice communications
  • Digital, where data is exchanged over the air, requiring computers or machines to interpret signals

For logging and awards these three categories are CW, Phone, and Digital modes.  The ARRL Logbook of The World (LoTW) adds a fourth category:  Image.  Collectively these 3 or 4 are known as mode Groups.

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Modulation Mode-  Modulation is the means to impress information on a radio signal.  It’s how a circuit puts our voice onto the radio signal through a microphone.  There are different forms (modes) of modulation which can be employed within each basic operating mode.

For example, typical modern HF transceivers support voice modes using AM, FM, and SSB modulation modes.  There are a few flavors of CW and dozens of digital modes (and the list keeps growing).  Just look at that mode group list link above.

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To further complicate matters we now have both traditional analog modulation for phone (voice) signals, and digital voice modulation as well.  Many digital modes simply modulate a SSB waveform using specific tones to represent data characters.  We live in an era where computers and radios are really working together to do amazing things.

Operating and modulation modes are hard to separate.  In fact, they sort of overlap and mash together.  Context of the discussion is key here; often it doesn’t really matter.

These two also play a role in the ITU classification of RF signals.  Refer to Types of Radio Emissions link.  Hams may occasionally log their mode according to this or a similar scheme.

Why do so many operational and modulation modes exist?  It’s largely for historic reasons as technology and electronics have advanced over the years.  In the earliest days of radio, only radiotelegraphy existed. Mode had no meaning as CW was the only possibility.   Then came voice technology and a second operating mode was born.  Going from original AM to SSB,  we then had modulation modes, adding FM as an improvement later.  Digital mode entered the scene after voice once people discovered they could encode audio signals to represent data; computer technology has made the digital mode wildly successful, if less personal, in recent years.  Image modes have been around since the early days of television but here again, computers have made them better and easier.

One other reason for different modes is Continue reading →

Why Hams Care About Solar Activity

AF5NP DX, HF (High Frequency), Ionosphere, Propagation, Solar, Sun

As we learned in an earlier post on the ionosphere, the real magic in ham radio is skywave propagation where HF  band (and sometimes VHF) signals can travel well beyond line of sight (over the horizon), even to the other side of the planet if conditions are right and radio waves may bend back to earth in the ionosphere.

The sun is largely responsible for energizing the ionosphere and affecting its quality (height, density, thickness, disturbance).  Unfortunately for hams, solar activity is highly variable, not constant.  There are periods of excellent skywave propagation when the sun is busy and then times of poor propagation when the sun is quiet.

Solar_Cycle_Montage
Montage of Sun’s activity over 10 years (solar cycle 23)

This topic is very complex and not completely understood.  Study is ongoing and radio amateurs have contributed greatly to the science; much has been learned in the last 100 years or so since radio became a real thing.   Great detail is found below in some excellent web links.  A brief summary of how solar activity influences the ionosphere is presented here:

Sunspot Numbers

  • Sunspot counts are a general indicator of solar activity
  • Propagation on higher frequencies is more influenced by solar activity than the lower frequency bands.
  • Ionospheric condition is influenced by the Earth’s magnetic flux lines.
  • Earth’s magnetic field is strongly influenced by solar wind (largely a day/night phenomenon but solar wind can spike with disturbances).
  • Solar flares, coronal mass ejections (CME), and coronal holes cause geomagnetic storms which affect or disrupt radio communication and create noise.

Solar/Space weather is a study of how solar events affect the earth’s magnetosphere.  A/K (long/short-term) indexes measure the stability of Earth’s magnetic field.

Hams worldwide who are active on HF and VHF bands pay a lot of attention to solar activity because of how it affects propagation and noise levels.  QRZ features N0NBH’s graphic summary of important solar and geomagnetic conditions on their main page as shown below.  Some hams and ham websites include this data on their own pages as well, so you may see this sort of info a lot.

S-T Data QRZ

Presently (2018-2019) we have days on end with no sunspot numbers, resulting in awful HF propagation (note sunspot number SN=0 above).

Solar Activity Level

Despite these poor conditions that limit decent phone (voice) and even CW (Morse) QSOs, hams can still make contact with domestic and international stations using some of the newer digital modes which can decode extremely weak (inaudible) signals.

We are hopefully approaching the end of the current solar minimum with dreams of increasing solar activity in the coming several years.

Solar activity is so important to hams that there are 16 related questions in the General class license exam question pool (only two with the limited privilege Tech pool).  Some 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 →