Tag Archives: Communications

Ionospheric Science and Amateur Radio from Heard Island

Aurora Australis seen from the International Space Station as it flew over Heard Island on September 7, 2015.  Image credit: NASA (public domain).
Aurora Australis seen from the International Space Station as it flew over Heard Island on September 7, 2015. Image credit: NASA (public domain).

High above Earth’s surface, roughly 60–1000 km up, is an intriguing part of Earth’s upper atmosphere called the ionosphere. High-energy light (mostly ultraviolet and X-rays) causes electrons to be stripped away from gas molecules and neutral atoms, forming ions (and free electrons). The incoming light is most intense at the upper edge of the atmosphere (before it is absorbed), but the density of atoms and molecules is higher at lower altitudes (with atmospheric density highest at the Earth’s surface), leading to a peak in ionization in an intermediate region. Much of the interesting action in the ionosphere is in the regions between 60–300 km up, where the electron density is highest (though still very low compared to sea level).[1]

Under many conditions, radio waves between 160 m and 10 m (with frequencies of 1.8–30 MHz) can be refracted by the ionosphere, enabling wireless communication around the globe. This long-distance propagation is, at least to me, a wondrous phenomenon.

Effectively, there is a low-frequency limit below which the radio waves are strongly absorbed by the atmosphere. At a sufficiently high frequency, the radio waves will not refract back down to Earth, and will simply pass into space. However, in the Goldilocks zone between those two frequencies (the lowest usable frequency and maximum usable frequency), propagation can occur.

Schematic cartoon of ionospheric propagation.  Image credit: NOAA (public domain).
Schematic cartoon of ionospheric propagation. Image credit: NOAA (public domain).

With the amount and intensity of sunlight reaching the ionosphere changing throughout the course of the day, year, and solar cycle, the maximum and lowest usable frequencies will change as well. Additionally, since not all of the globe is illuminated at the same time, these limiting frequencies will vary spatially. Consequently, the maximum usable frequency in one location may be below the lowest usable frequency somewhere else, and no radio contact can be made between those points at that time.

Scattered around the world are many, many radio stations operated by licensed amateurs (sometimes also called hams; etymology unclear).[2] One aspect of the hobby which many amateurs enjoy is making contact with amateurs in other countries around the world. Just like birders have a life list of the species of birds they have seen, amateur radio operators often keep a list of other countries and territories they have contacted, splitting this list further by frequency and operating mode (Morse code, voice, or digital). Currently, there are 340 recognized entities worldwide.[3] Of those 340, many are small reefs, islands, or archipelagos, and may not have any permanent population—such as Heard Island, making them very rare. The last time Heard Island was heard on amateur radio was in 1997. It’s presently the longest-inactive of the 340 entities and ranks around #5 on most-wanted lists. Many amateurs have been looking forward to this expedition for a long time, and have been very generous in supporting it financially.

On Heard Island, our team will put up several amateur radio antennas at Atlas Cove, and set up approximately 6 radios. We will then make contacts with as many stations as we can on the various amateur frequencies, in a combination of voice, Morse code, and digital modes, using the callsign VKØEK. Contacts are extremely brief which helps keep the throughput high, giving more stations a new entity for their list and us a more statistically significant sampling of the ionospheric conditions.

Here’s how a voice contact might proceed:

[VKØEK]: Victor kilo zero echo kilo, listening up
[Din of thousands of stations calling with their callsigns]
[VKØEK]: Kilo zero bravo bravo charlie, five nine4
[KØBBC]: Five nine, thanks
[VKØEK]: Thank you

It’s not a long, drawn-out conversation, but is enough to be logged on both ends as having happened. Under ideal circumstances, within a minute or two, that contact will be shown on a near-real-time map of contacts from Heard Island. With luck and the cooperation of stations around the world, we should be able to log >100,000 contacts over the three-week period and gather some very interesting data about which frequencies work to which places at which times.

Simulated near-real-time map of contacts with Heard Island, shown on the DXA3 website.  QSO is radio shorthand for contact.  Numbers under Currently Working heading are approximate wavelengths in meters, corresponding to the amateur radio allocations.
Simulated near-real-time map of contacts with Heard Island, shown on the DXA3 website. QSO is radio shorthand for contact. Numbers under Currently Working heading are approximate wavelengths in meters, corresponding to the amateur radio allocations.

Of course, one other advantage of the amateur radio operation is that it is yet another means of communication in the case of an emergency. While we hope that no emergency communications are needed of any type, and we have a number of satellite communications options, amateur radio provides one more level of redundancy, and has been shown to be reliable in places where little or no infrastructure exists (e.g. following major earthquakes, hurricanes, etc.).

The ionosphere does amazing things, and our amateur radio operation will both yield data on the ionosphere as well as make many thousands of amateur radio operators happy that they were able to contact a new entity.

*** Notes and References ***

[1] For a point of reference, airplanes generally fly at a height of 10–13 km, the highest jet aircraft flight record is 37.6 km, and the International Space Station is at a height of roughly 340 km; even high-altitude weather balloons and rarely exceed 40 km.

Features of Earth's atmosphere.  Image credit: NOAA (public domain).
Features of Earth’s atmosphere. Image credit: NOAA (public domain).

[2] In the US, getting an entry-level amateur radio license requires passing a 35-question multiple-choice test on terminology, regulations, basic electronic theory, and operating practices, and is roughly equivalent to a written driver’s exam. Knowledge of Morse code is not required. For more on US licensing, see this page.

[3] Islands and outlying territories beyond certain distances from the main entity are considered separate, so Hawaii, Alaska, Puerto Rico, and the US Virgin Islands all count as separate entities even though they are US states, territories, or possessions. The gritty details on criteria for listing as separate entities is found in section 2 here.

[4] “Five nine” is a signal report, meaning “I hear you loud and clear”.

Satellite Communications

Geostationary orbits, used by some communications satellites.  Image credit: Lookang (CC-BY-SA).
Geostationary orbits, used by some communications satellites. Image credit: Lookang (CC-BY-SA).

One important aspect of field work in remote places is keeping lines of communication open. At a minimum, the ability to call for help is needed. Sending status updates, checking email, talking with loved ones, and a number of other uses are good to have. Even in this day and age, though, not every remote place has good cell phone coverage. These places are where satellite phone systems are extremely useful.

There are two main types of satellite systems: geostationary satellite systems, and low-Earth-orbit satellite systems.

Geostationary satellite systems have satellites over fixed locations above Earth’s equator, at an altitude of roughly 36,000 km (22,000 mi). Geostationary satellites are nice in that they are always in the same spot relative to a location on Earth, so there are no signal hand-offs where calls may drop, nor do the stations on the ground need to have any kind of tracking mechanism to keep the antenna pointed at the satellite. Unfortunately, because the geostationary satellites are located over the equator, they do not work well pole-ward of 70° latitude, because they are too close to the horizon for reliable, interference-free signals. Geostationary satellites also have a noticeable delay, because the round-trip light time is a minimum of ~0.25 seconds, and the time to receive a response back doubles that.

Low-Earth-orbit satellite systems require many more satellites, but the satellites are much closer to Earth, generally only 650–1100 km above the surface. Many of these satellites are in a polar or near-polar orbit, which gives them good coverage near the poles. Each satellite is only over any given area for 4–15 min, so hand-offs are necessary (and are not always reliable). One advantage of low-Earth-orbit systems is that the transmitter and antenna on the ground do not need to be especially powerful or carefully aimed. Low-Earth orbit systems have substantially less data throughput than the geostationary systems (9600 kbps for LEO vs. 60–512 kbps for geostationary). For reference, the LEO throughput is much less than dial-up modems, and geostationary throughput is up to 10x higher than dial-up, though still far short of broadband internet access (4 Mbps down, 1 Mbps up).

I mentioned that the antennas (and power) for a geostationary satellite setup need to be better than ones for low-Earth orbit satellites. This is because of the inverse-square law, where the as the distance is increased, the power which reaches the receiver drops by the square of that increase. Think of standing outside at night with a friend (representing the ground station and satellite), and each of you has a flashlight (representing the radio transmitters) and eyes (the radio receivers). When you are close, the light is very bright, and you probably have to look away. As you move away from each other, the lights appear dimmer and dimmer. Each time you double the distance between you, the brightness of the light dims by a factor of four. If you need a certain level of brightness at the receiver (your eye, or the satellite antenna), then there has to be either a sufficiently bright light shining (power level), or it needs to be focused enough—and harvested enough by a sufficiently large receiver—to achieve that level of signal.

Inverse-square law in action; as the distance increases (e.g. from r to 2r), the area the energy is directed over increases as the square of the distance (e.g. from 1 to 4 units).  Image credit: Borb (CC-BY-SA).
Inverse-square law in action; as the distance increases (e.g. from r to 2r), the area the energy is directed over increases as the square of the distance (e.g. from 1 to 4 units). Image credit: Borb (CC-BY-SA).

With a difference in altitude of ~40x between low-Earth orbit and geostationary orbit, there is a difference of 1600x in the signal level, all else being equal. For that reason, satellite phones for low-Earth-orbit satellites can get away with less powerful radios and smaller antennas that are less sensitive to proper positioning. It’s handy to not need exact positioning for the low-Earth-orbit satellites, because their quick movement across the sky can be difficult to track without a motorized, computer-driven antenna. Mobile or ship-based satellite communication systems tend to rely more on the low-Earth-orbit satellites precisely because the aim of the antenna is much less important. Nobody wants to try to hold an antenna pointing in a certain direction while pitching about on a ship in 4 m seas in the wind and the cold.

As an amateur radio operator, one thing I enjoy doing is going outside when the International Space Station is flying over, and listening to the radio signals it sends down. During the morning or evening passes on clear days where the space station is visible, it is quite easy to point in the right direction. Spot the station, then point your hand-held antenna toward it. During the day, in the depths of night, or when it’s cloudy, tracking the station can be more difficult (at least without computer assistance). Still, it’s pretty neat to hear astronauts answering questions from the local middle school students, all the while knowing that the signal coming from the space station is coming directly to your radio, no internet or commercial broadcast station required.