Distance

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.

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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 →

Technician Class Distant Contacts

AF5NP Distance, DX, Echolink, EME, General Class, IRLP, Moonbounce, QSO, Technician Class

Making radio contact over great distance is one of the more interesting aspects of ham radio.  For many radio amateurs, it’s their main pursuit.

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Working DX (ham-speak for distance) commonly means contacting a station outside your own country but Alaska and Hawaii are certainly DX stations by distance, and in reality good DX is cross-country in a large entity such as the USA.

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Unfortunately for US hams, the entry-level Technician class license permits rather limited opportunities for making radio contact beyond line of sight.  Don’t despair if you have only a Tech license and want to do more than chat with locals on a repeater.  There are six ways for a Technician licensee to communicate outside of town, outside your state, or even outside the country.  We will briefly mention these here and perhaps cover them in greater detail in future posts.

DX is commonly accomplished on the high frequency (HF) bands due to ionospheric refraction or bending of radio waves.  HF signals routinely reach the other side of the planet and places in between.  So for most hams chasing DX or just working beyond the local area means having a HF transceiver and antenna for the band(s) of interest.

The first two opportunities for Technician licensees to communicate over distance involve traditional HF equipment:

1) USA Technician class operators have privileges to operate CW mode (Morse code) on 80m, 40, 15m and 10m HF bands with a 200W power limit.  This is how hams used to get started in amateur radio and while CW is still quite popular, it is intimidating to many new folks.  So opportunity #1 may not be appealing to many Techs unless they want to learn Morse code (a fun skill, by the way).

2) USA Technicians also have SSB voice and  digital (data) privileges on 10m, again with a 200W limit.

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This is the only HF voice privilege for this class and the frequency range is very narrow.  The data mode privilege is really helpful here because it allows Techs to work popular digital modes such as JT, FT, PSK,  Olivia and MSK.  However, 10m propagation is highly dependent on solar activity.  The band can be inactive or slow for weeks or months at a time.  So Technicians may be frustrated over a lack of activity for opportunity #2.

Tech license DX opportunities #1 and #2 above on HF bands are admittedly limited by mode and/or active band.  This alone is excellent motivation to upgrade to a General class license.  Consider this possibility.  It’s not a huge leap in learning and study to move up, very achievable for most people.

We know that the VHF and UHF bands for which Technician licensees have full privileges are generally limited to local communication because of line of sight propagation.  Repeaters and/or tall antennas can extend this range but DX is not readily achieved using normal methods.  However, there are four clever technologies that enable DX on VHF/UHF bands: 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?)

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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 →