Excellent 43 mb Propagation, 10/11 mb Operators Put On Suicide Watch

Old Sol has been quiet lately. Far too quiet for the 10 and 11 meter band guys. As I’m typing this, the solar flux is back into double digits, at 95. The Sun Spot Number (SSN) is officially 24, but you need to squint real hard to actually see any sunspots:

Sunspot SunSpeck group 1452 has pretty much rotated out of view, taking the meager solar activity we’ve had with it.

The NOAA/NASA/Space Weather prediction boys promise that we’re still a year away from the peak of cycle 24, and activity will increase.

Go up. Yes, it will go up any time now, just you wait. Hey! Look over there! Global Warming!

Meanwhile, back in the real universe, the background x-ray flux is at B1 levels.

So what does all this mean for us DXers? The lower solar activity has several major effects. First, the highest frequencies that can be propagated are lower, in many cases much lower. During a solar cycle maximum with high activity, the higher bands are often open 24 hours a day. With the lower activity we’ve been having, this is not this case. Yes, 10 meters is still open at times, but not nearly as much, or with the good conditions that have been experienced in the past. So operators and listeners need to move down to lower frequencies.

The foF2 frequencies are correspondingly lower, which means that a given band (including 43 meters) will go long earlier in the evening. Operators may want to adjust their schedules accordingly, and consider transmitting a little earlier to reach a semi-local audience. OTOH, they’ll end up reaching more distant listeners earlier in the evening as well.

Second, D-layer absorption is lower, due to decreased x-ray flux from the Sun. This means that lower frequencies are not attenuated as much, which is a good thing, since in many cases that’s all that is propagating. The last few days, I’ve been hearing 48 mb (6 MHz) Europirates fade in as early as 2 hours before local sunset. And once the Sun does set, their signal levels increase to really strong levels. Likewise, US pirates such as Wolverine Radio have been reported across the US and into Europe with incredible signal levels.

Third, the lack of major solar flares and coronal streams affecting the Earth means that geomagnetic conditions have been very stable. No geomagnetic storms means stronger signals, and less fading.

The net result is that reception conditions for 43 meter band pirates has been extremely good lately. Lots of operators and listeners have been taking advantage of the excellent conditions, loggings are way up.

There is a coronal stream expected to start impacting the Earth around the 13th or 14th of April, so we’ll have to see what effect, if any, that has on conditions. Until then, enjoy the great propagation!

Solar Storms (plus Solar Hurricanes, Typhoons, and other ways the Sun will vaporize us or even worse, possibly cause your iPhone to not work)

Over the past few years, there has been dramatically increased media coverage of solar flares, and the effects they can have on the Earth, primarily on our electrical distribution and communications systems. The emphasis has been on the ability of the flares to cause geomagnetic storms on the Earth, which then can induce currents in our electrical power grids, causing them to go offline from damage. There has been a tremendous amount of fear instilled in the public by the hundreds, if not thousands, of news articles that appear every time there is a solar flare.

Those of us who are shortwave listeners or amateur (ham) radio operators are typically familiar with solar flares, and some of the effects they can cause. To summarize:

A solar flare is a sudden brightening of a portion of the Sun’s surface. A solar flare releases a large amount of energy in the form of ultraviolet light, x-rays and various charged particles, which blast away from the solar surface. The x-rays can have an almost immediate effect on the Earth’s ionosphere, the layer of charged particles above the atmosphere, which allows for distant reception of shortwave radio signals. I discuss the effects of x-rays on the ionosphere this earlier article. Energetic solar flares can cause what are known as radio blackouts, where all of the shortwave spectrum appears to be dead, with few or no stations audible. Other communications bands, such as AM / medium wave (MW between 526-1705 kHz), FM, TV, and cellular phones are not affected. Just shortwave. Also, the portion of the Sun producing the flare must be roughly facing the Earth to have an effect, and only the sunlit portion of the Earth is affected.

The solar flare can also cause a Coronal Mass Ejection (CME), which is a burst of energy, plasma, particles, and magnetic fields. The CME typically takes one to three days to reach the Earth. When it does, it can cause a geomagnetic storm, which is a disruption of the Earth’s magnetosphere. The magnetosphere is a region of space surrounding the Earth, where the magnetic field of the earth interacts with charged particles from the sun and interplanetary space.

The CME can produce very high radiation levels, but only in outer space. If you’re an astronaut on the International Space Station, this could be a concern. If not, you don’t really have much to worry about. High altitude airline flights can result in somewhat higher than usual radiation doses, but high airline flights always result in higher than usual radiation doses, due to less atmosphere protecting you from cosmic radiation. You might just get a little more especially if you fly over the North Pole. Or over the South Pole, but I don’t think there are too many of us who do that.

The effects of a geomagnetic storm:

The Earth’s magnetic fields are disturbed. This can cause compass needles to deviate from their correct direction towards the poles, and has been frequently mentioned in medieval texts.

Communications systems can be impacted. As with solar flares, shortwave radio is most affected. AM can also be affected to some degree. FM TV, and cell phones are not affected.

Back in 1859, there was a large geomagnetic storm, often called the Carrington Event because the solar flare that caused it was seen by British astronomer Richard Carrington. The effects were dramatic. Aurora were seen as far south as the Caribbean. Telegraph lines failed, and some threw sparks that shocked operators. Storms of this magnitude are estimated to occur about every 500 years. Other very large geomagnetic storms occurred in 1921 and 1960, although neither was the magnitude of the 1859 storm. The term “Carrington Event” has now come to mean an extremely large geomagnetic storm that could cause devastating damage to the communications and electrical systems around the world. But these forecasts are often based on the notion that, with more communications and electrical systems in place, we are much more reliant on these systems and vulnerable to disruption, meanwhile ignoring the fact that we better understand how geomagnetic storms cause damage, and what can be done to prevent it. Remember, this was 1859, and very little was even known about how electricity worked, let alone the effects of geomagnetic storms. This was in fact the first time that the relationship between solar flares and geomagnetic storms was established.

Communications satellites can be affected due to the higher radiation levels and unequal currents induced in various parts of the satellites. This could cause the satellites to temporarily malfunction, or even be damaged (which could affect FM, TV, and cell phone calls, which would otherwise be unaffected). As satellites are always in a high radiation environment, they are protected, and it would take very severe conditions to cause extensive damage.

Between 19 October and 5 November 2003 there were 17 solar flares, including the most intense flare ever measured on the GOES x-ray sensor, a huge X28 flare that occurred on November 4. These flares produced what is referred to as the Halloween Storm, causing the loss of one satellite, the Japanese ADEOS-2. Bear in mind that there are almost a thousand active satellites in orbit.

GPS navigation can also be affected, due to variations in the density of different layers of the ionosphere. This can cause navigation errors.

But the effect that, thanks to media hype, everyone is most concerned about is the possibility of a solar flare causing a geomagnetic storm that destroys the entire power grid, leaving virtually the entire United States without power for weeks or even months. The good news is that this is highly unlikely to happen.

Here’s the scenario: The geomagnetic storm causes currents to be induced in the wires that make up the long distance transmission lines that connect the various electrical power plants and users across the United States, aka the power grid. If these currents become large, they can damage equipment such as transformers, leading to widespread power outages.

And indeed this happened, on a much smaller scale, on March 13, 1989. A geomagnetic storm caused ground induced currents that severely damaged seven static compensators (devices that are used to regulate the grid voltage) on the La Grande network in the Hydro-Quebec, Canada power grid, causing them to trip or shut down automatically. The loss of the compensators allowed fluctuations in the grid voltage, causing damaging to other devices. The net result was that over 6 million people in Quebec and the Northeastern United States were without power for about 9 hours. Another million were without power after the 9 hours. Parts of Sweden also had electrical power disruptions.

While being without power for 9 hours, or even several days, sounds dreadful, especially in this age of constant communications, it does happen routinely. Hurricanes and tropical storms often cause millions to lose power outage each year, as do snowstorms, ice storms, and thunderstorms. Even heat waves have caused massive blackouts. I was without power for a week after Hurricane Isabel in 2003. The concern with an extreme geomagnetic storm, such as a repeat of the Carrington Event, is that critical components such as large transformers could be damaged, which can take time to repair or replace. And there’s the fear that widespread damage to the electrical grid could result in more components being damaged than spare parts exist, causing even longer delays until they can be replaced.

In the two decades since the 1989 event, more protective devices have been installed, and electrical transmission line operators are more aware of the damage caused by induced currents from geomagnetic storms. Preventative measures, such as temporary blackouts for several hours until conditions stabilize, can prevent much of the damage from a large geomagnetic storm. The advanced warning of geomagnetic storms now possible due to the satellites that are continuously monitoring the Sun and the Earth’s geomagnetic field can give electrical transmission line operators the advanced warning they need to take preventative measures.

Also, the 1989 event occurred in Quebec, which is at a very northern latitude. Geomagnetic storms tend to be stronger near the poles, and less severe as you move towards the equator (much like how the aurora is commonly seen near the poles, but not elsewhere).

It’s also worth noting that there are actually three electrical grids in the United States: an Easter, Western, and Texas grid. They are not currently connected to each other, although there are discussions to do so.

Finally, while a repeat of the Carrington Event is possible, it is extremely unlikely (remember, they are thought to occur about once every 500 years). There are far more important things to plan for, such as blizzards, hurricanes, tornadoes, and even severe thunderstorms, which routinely do occur. It is certainly more prudent to prepare for events like these, by keeping batteries, portable radios, canned food, and jugs of water on hand, than to worry about an event that probably won’t happen again for several hundred years.

So, why all the media frenzy and public concern over solar storms?

First, the Sun operates on a roughly 11 year solar cycle. Solar activity, including the appearance of sunspots and solar flares, peaks about every 11 years, and then fades until the next solar peak. There’s a solar peak occurring right about now. The last one was in 2001. This was before Facebook, Twitter, and everyone spending several hours a day on the internet, obsessing about the crisis du jour. Or crisis of the year in this case. Back in 2001, very few people even knew there was such a thing as a solar flare, other than space scientists and ham radio operators.

Those of us who have been involved with radio related hobbies for some time are used to the 11 year cycle. As an SWL since 1978, I’ve witnessed several solar cycles. During a solar peak we get many more flares which disrupt reception, although the overall higher level of solar activity is actually beneficial to shortwave propagation. Plus, it’s more likely that we’ll get to see the aurora. Then things calm down for many years, until the next solar peak.

There’s also been a substantial increase in advocacy by scientists and other public officials for increased spending on solar flare / geomagnetic storm research and related programs. Obviously this is justified to some extent, as we are much more reliant upon technology, and even just electricity, than we were decades ago. Still, I wonder if things are being exaggerated just a wee bit. Government officials and those involved in research have a vested interest in increasing their budgets and staffs – it’s job security for them. I’m not suggesting any malice, pretty much everyone thinks their job is important, especially those in the scientific field. It’s human nature.

This increased advocacy has resulted in increased media coverage as well. I’m far less sympathetic here. The motto of many news organizations seems to be “If it bleeds, it leads”. Pretty much every time there’s a solar flare, there’s a flurry of news articles announcing impending doom. The titles are amusing, not only are there SOLAR STORMS, but also SOLAR HURRICANES, SOLAR TYPHOONS, and SOLAR TSUNAMIS. I haven’t heard of any SOLAR TORNADOES, but maybe next month. Invariably the articles describe how a solar flare can wipe out the entire power grid, sending us all back to the stone age. And this might be the one that does it! Of course, a day or two later, when the CME arrives and little happens other than poor shortwave radio listening and some enhanced Northern Lights, there’s no followup article. Although if there was, I’m sure it would state that while we dodged the bullet this time, the next flare will surely fry us all. And our iPhones.

Some examples:

Nasa scientists braced for ‘solar tsunami’ to hit earth

The Daily Telegraph disclosed in June that senior space agency scientists believed the Earth will be hit with unprecedented levels of magnetic energy from solar flares after the Sun wakes “from a deep slumber” sometime around 2013.

Cities blacked out for up to a year, $2 TRILLION of damage – with a 1 in 8 chance of solar ‘megastorm’ by 2014

Imagine large cities without power for a week, a month, or a year. The losses could be $1 to $2 trillion, and the effects could be felt for years.

‘A longer-term outage would likely include, for example, disruption of the transportation, communication, banking, and finance systems, and government services,’ the NRC report said, it was reported on Gizmodo.

‘It could also cause the breakdown of the distribution of water owing to pump failure; and the loss of perishable foods and medications because of lack of refrigeration.’

Solar Flare: What If Biggest Known Sun Storm Hit Today?

Repeat of 1859 space-weather event could paralyze modern life, experts say.

A powerful sun storm—associated with the second biggest solar flare of the current 11-year sun cycle—is now hitting Earth, so far with few consequences. But the potentially “severe geomagnetic storm,” in NASA’s words, could disrupt power grids, radio communications, and GPS as well as spark dazzling auroras.

The storm expected Thursday, though, won’t hold a candle to an 1859 space-weather event, scientists say—and it’s a good thing too.

If a similar sun storm were to occur in the current day—as it well could—modern life could come to a standstill, they add.

The news articles are bad enough, but I suspect the fact that 11 years ago no one saw articles like this, or even knew solar flares existed, has convinced a lot of the public that solar flares (of this magnitude and frequency of occurrence) are a new phenomena. It probably doesn’t help that this is the year 2012, and we’ve had the Mayan 2012 END OF THE WORLD nonsense to deal with for the last decade or so. I wonder if anyone has retconned Mayan history into them having a solar observatory and been aware of the 11 year solar cycle, and how it would peak in 2012, destroying the Earth. Maybe they even had an x-ray satellite in orbit. I bet the aliens that helped them build their pyramids left them one. The grays are helpful, like that.

Perhaps the most ironic part of this entire saga is that the 2012 solar cycle peak is forecast to be extremely low. Here’s the latest forecast and current progress through the cycle, click to enlarge it:

The peak smoothed sunspot number (SSN) is forecast to be about 60, vs the 120 for the previous cycle. The lower peak SSN means lower overall solar activity. That means fewer flares, and they should (overall) be less severe. The peak is also forecast to be in 2013, so I’m not sure how that works out for all the 2012 Doomsayers.

To put this further into context, here’s a graph showing all the previous solar cycles:

The red arrow points to the cycle peaking in 1928, the forecast at the time (2009) was that the cycle we’re in now would be similar to that one, it’s since turned out that activity is even lower.

The largest peak is Cycle 19, from the 1950s. Many older ham radio operators have fond memories of Cycle 19, when radio propagation conditions were excellent. They were hoping for a repeat with Cycle 24, but that is clearly not the case. And Cycle 25 is currently being forecast by some to be even lower than Cycle 24, although it’s not worth putting much, if any, stock into long range solar cycle predictions. Predictions for our current cycle (24) from just a few years ago had it being as strong as, or even stronger than, the previous cycle, which is clearly not the case.

The period marked as the Maunder Minimum on the above graph was a period of extremely low solar activity around the late 17th century. Very few sunspots were noted during this time period.

While we are indeed entering the peak of a solar cycle, which means more solar flares (and more powerful flare), which can have impacts on the Earth, I believe the historical evidence shows that the doomsday scenarios proposed by many alarmists are not warranted. I would suggest checking with various websites such as http://www.spaceweather.com/ to keep track of when a solar flare has occurred. Not to panic that the end is near, but to know when to go outside and look at the Northern Lights. They can be quite beautiful.

The Effects of an M8 Solar Flare

We had an M8.4 solar today, commencing at 1715 UTC, and ending at, well, it still seems to be going on, the x-ray flux level is still C3 at 2300 UTC.

The effects were rather dramatic, for those of us on the sunlit side of the Earth. First, here’s a graph of the x-ray intensities of the flare itself, as measured by the GOES-15 weather satellite (in geosynchronous orbit around the Earth):

The effects were dramatic, virtually all of HF was completely silent here, just static. The intense x-rays from the flare caused strong ionization of the D layer of the ionosphere. The D layer absorbs radio waves, it does not reflect them like the E and F layers that we rely on for shortwave propagation.

Here’s a graph showing the absorption at HF radio frequencies caused by the flare, as displayed by DX ToolBox:

You can view the signal strengths for various frequencies as recorded by my dedicated SDR setup here: http://www.hfunderground.com/propagation Take a look at various stations such as CFRX 6070 kHz and CHU 7850 kHz, and see how they completely faded out during the flare. They also are not present at night, which is normal.

What’s the Best Time of the Day to Hear a Pirate Station on 43 Meters?

That question could also be phrased “What’s the Best Time of the Day for a Pirate to go On the Air on 43 Meters?”

The answer to both of those questions depends on solar condition, how far apart the operator and the listener are, and their relative locations.

The above graph (click for a larger image) shows the signal level of CFRX, which transmits from Toronto, Ontario on 6070 kHz with 1 kW of power. It is located about 300 miles to the north-north-west of my location. 6070 kHz is close to the 6800-7000 kHz 43 meter pirate band, and the distance is comprable to that of many pirate stations, so I believe it is a good analog for the daily variation of signal strengths that most North American pirate radio stations will experience when operating under NVIS propagation.

The data starts at 0700 UTC on January 31, 2012 and runs until 1200 UTC on February 3, 2012. The data was captured with an SDR-14 connected to a 132 ft T2FD antenna. Custom software gathers signal strength data for several specified frequencies.

Several things are quite apparent:

You can see that at about 0130 UTC every day, the signal strength suddenly drops. This is when the station goes long, and short distance propagation is no longer possible via NVIS. This is due to the ionization level of the F2 layer decreasing to the point where steep angle radio waves are no longer reflected back to Earth, but pass through the ionosphere into space. Generally there appears to be a two-step process:

    The signal suddenly drops to a lower level. It stays at that lower level for a while, with a slight decrease in signal over that time.
    The signal then starts dropping more quickly over the rest of the night, reaching a minimum just before sunrise.

Likewise, at about 1200 UTC each day, the signal strength suddenly increases again. This is when the F2 layer ionization has increased to the point where NVIS propagation is again possible. Sometimes there is an increase in signal level earlier than this. The morning of February 1, for example, the signal came up during the middle of the night for several hours, then went back down again. That was a fairly unusual night, propagation-wise, compared to the other nights.

There are four primary factors that affect these two times of the day (0130 and 1200 UTC in this case):

    First, the distance between the listener and the station (and their relative locations, of course). The closer together, the steeper the angle of incidence radio waves to the ionosphere, and the earlier in the evening (and later in the morning) the station will go long. Stations further away will go long later and return earlier, because the radio waves hit the ionosphere at a more shallow angle. The time of day is also dependent on the longitudes of the two stations, the further west they are, the later in the UTC day it will be, due to the location of the Sun over the Earth.
    Second, the frequency used. The higher the frequency, the earlier the ionosphere will stop supporting NVIS, and the longer it will take in the morning for the ionization levels to return to a sufficient level to support it again.
    Third, the day of the year. We’re in winter now, with relatively short days and long nights. As we get closer to spring and summer, the days get longer, and the band will be open for NVIS longer.
    Fourth, the solar activity, which affects how strongly ionized the F2 layer gets. This also affects the D layer, which can attenuate signals, which we’ll get to in a moment. Changes in solar activity produce some of the day to day variations in CFRX signal strength patterns in the graph. Geomagnetic variations probably account for variations as well. These of course are due in large part to previous solar events, such as flares.

Next, note that while the signal level does suddenly increase in the morning, it then starts to decrease again, bottoming out around 1700 UTC, which is local noon. This is due to the attenuating effect of the D layer of the ionosphere. The D layer absorbs radio waves, rather than reflecting them back to Earth. The stronger the D layer, the more absorption there is. Lower frequencies are also more strongly absorbed. This attenuation peaks at local noon, when the Sun is highest in the sky. The drop in signal level at noon is around 12 dB, or 2 S units.

So while the Sun strengthens the F layer which supports propagation, it also strengthens the D layer, which attenuates it. These are competing factors. X-Rays from the Sun increase the D layer absorption. The background X-Ray flux is a good indicator of how strong (relatively) the D layer is. Solar flares can cause dramatic increases in D layer ionization, leading to severe fading and even shortwave blackouts.

Another thing to note is that the signal level in the morning is not as strong for as long as it is in the evening. After noon, the D layer starts to weaken when the ions begin to recombine. The F layer also weakens, but this takes longer to occur. So in late afternoon and early evening, we have an extremely weak D layer, yet still have a fairly good F layer, giving us strong signal levels. Then, finally, the F layer weakens to the point where NVIS operation is no longer possible, and the band goes long, sometimes dramatically.

We can use CFRX’s known 1 kW transmitter power and estimate the received signal levels if they were using a lower power level, typical with pirates. A 100 watt transmitter will be produce signal levels 10 dB weaker than CFRX’s 1 kW. Likewise, a 10 watt transmitter will be 20 dB weaker. For these measurements I used an SDR-14 receiver and a 132 ft T2FD antenna. Listeners with more modest setups are going to have a weaker signal.

Using the February 1st data, CFRX had a signal of about -60 dBm at 1300 UTC. This is S9+13 dB. A 100 watt transmitter would produce a signal of about -70 dBm, or just over S9. A 10 watt transmitter would produce a -80 dBm signal, about S8.

At high noon, CFRX was about -70 dBm, or very close to S9. A 100 watt transmitter would be -80 dBm, about S8, while a 10 watt transmitter would be -90 dBm, or about S6.

At around 0000 UTC, CFRX was about -56 dBm. A 100 watt transmitter would be -66 dBm, or S9+7 dB. A 10 watt transmitter would produce a signal of -76 dBm, about halfway between an S8 and S9 signal.

After the band went long, but while CFRX was still audible, the signal was about -80 dBm. A 100 watt transmitter would be -90 dBm, or about S6. A 10 watt transmitter would be about -100 dBm, or midway between S4 and S5. Noise levels on this band are about -105 dBm, so the signal to noise ratio (SNR) of the 100 watt station would be only about 10 dB, not very good. For the 10 watt station, it would be 0 dB, meaning that you would not be likely to hear much of anything.

There are several points to take away from this:

    NVIS propagation, which most pirates are using on 43 meters, is presently most effective in the late afternoon and early evening. As we move into summer this will probably shift somewhat later, I’ll have to run some more measurements in several months to see what actually happens.
    NVIS is also fairly good in the morning, but signal levels will likely be weaker than in the day. I’ve often noticed this myself: Radio Ga Ga is usually very weak here in the morning, but comes in much better in the early evening.
    Signal levels from NVIS will likely be weaker around noon, due to the stronger D layer. Propagation is still quite possible, of course, and signal levels may be good, especially for shorter distances and higher power levels. You’re going to have a difficult time reaching the east coast of the US from Montana with a 10 watt grenade at high noon on 43 meters, however.
    Signal levels at night for stations trying to use NVIS propagation will be extremely weak, if the station is even audible at all. Note that this is only the case for stations that are close to the listener. The further away the station is, the more shallow the incidence angle of the radio waves and the ionosphere. This means that the station will go long later in the evening, or not at all. Likewise, an operator trying to get out further, or a listener trying to hear more distant stations, will want to try later in the evening after the band has gone long (which of course is why we call it going long in the first place).
    Operators can use the time of the day their transmit to (roughly) control where they will be heard. An operator from Guise Faux’s “southwest corner of Pennsylvania” will reach an audience in a several hundred mile radius during the middle of the day, perhaps slightly further in the morning (after sunrise) or early evening. After the band goes long, say after 0100 UTC right now, he’ll start to reach listeners further away, while local listeners will be in the skip zone. As the evening goes on, the skip zone will continue to grow in radius, but he’ll be reaching listeners further west, and possibly eventually to the west coast.

    Conditions will change with the seasons and the solar activity level. What is true now will not be true six months from now, when we’re in summer. A change in solar activity levels will also affect propagation conditions on 43 meters.

The NVIS Near Vertical Incident Sky Wave article has the necessary information for estimating when propagation will go long, based on the distance between the stations and the current ionosphere conditions. Operators and listeners may want to take a look at the current conditions to gauge how propagation will be. While not a guaranteed way of computing of exact conditions, it is a good way to get a feel for how the band will perform. Likewise, take a look what solar conditions were like that day, whether there were any major flares, for example.

Graphs of Realtime HF Signal Levels

While it’s useful to forecast propagation conditions, it’s even more useful to know what the actual propagation conditions are. Propagation forecasting is somewhat like weather forecasting, although slightly less accurate.

I wanted to measure (and store for future reference) the signal levels from several shortwave stations from various parts of the world, transmitting on a range of frequencies. These stations can act as references for determining what propagation conditions are like to that part of the world, on a certain frequency or band, anyway.

One way to do this would be to step a radio through a list of frequencies, measuring the signal level and recording it. The problem is that you need to sit on a given frequency for at least some short period of time, to measure the signal level. And, if you’re only on the frequency for a second or two, that recorded signal level may not be characteristic of the actual signal level. You could have been monitoring while there was a burst of interference, causing a false high signal level reading. Or during a sudden deep fade, causing a weaker signal. And the longer you sit on one frequency, the less time you’re spending on other frequencies. You’re not continuously monitoring, but taking short snapshots.

But there is a solution. Once again, SDR (Software Defined Radio) to the rescue!

In this setup, an RF Space SDR-14 Software Defined Radio is connected to a 132 ft T2FD (Tilted Terminated Folded Dipole) antenna.

Custom software is continuously reading A/D (Analog to Digital Converter) values from the SDR-14 (in real, not complex, mode). The A/D sample rate is approximately 66.67 MHz. Blocks of 262,144 readings are taken, and an FFT is performed. The result is an array of signal strength readings for the entire HF spectrum, 0 to 30 MHz, in 254 Hz steps.


For frequencies of interest, the software then computes the signal strength in dBm over a +/-3 kHz bandwidth around a center frequency. This is computed approximately twice per second, and these readings are averaged over one minute. They are then uploaded to the web server, where they are stored, and graphs are made on demand when a user loads the page. These graphs show the last three days worth of readings. (Possibly less if I just started taking readings for that frequency)

The URL for accessing the graphs is http://www.hfunderground.com/propagation/

You will get a list of frequencies, with a brief description of the station on that frequency. Click on a frequency to get a graph of about three days worth of signal readings.

Several things can be readily observed:

For the lower HF frequencies, signal levels are very weak during the daytime, due to absorption by the D layer. They then slowly rise as the Sun sets, stay high overnight, and then go back down again as the Sun rises.

For higher frequencies, say 6 and 7 MHz stations operating in NVIS mode such as NAA on 6726 kHz, you can see a sudden decrease in the signal level as the station goes long in the evening, and then an increase again when the Sun rises, and the F layer increases in strength. The signal does not always completely go away during the night, but it is significantly weaker. There are also periods at night when the signal level goes up and down. This could be the actual signal from the intended station, or possibly another station located elsewhere in the world.

The effect is much more pronounced for even higher frequencies, such as WWV on 20 MHz.

The recording for 10 MHz often shows WWV cutting out around local midnight, then the signal level goes back up again in the early morning, but before sunrise. I believe in this case we’re actually getting a signal from WWVH in Hawaii.

I’m also recording 25,555 kHz, which is a mostly open channel. My goal is to observe radio noise from Jupiter on this frequency.

The aviation weather frequencies (6604 kHz for example) do not have continuous transmissions, there are gaps. This is readily observable by seeing the steps in signal level.

You will often see spikes in the graphs. This is mostly likely due to local noise, it could also be to brief transmissions on the frequency. There are ionospheric sounders that sweep across HF, as these pass by the frequencies being observed, they will cause a brief increase in the measured signal level.

You may also notice occasional gaps in data, the ancient computer the SDR-14 is running on (under Windows 2000) seems to develop USB issues every dozen or so hours. I need to try to set it up on another computer and see if that helps. Worst case I may try to rig up some sort of a Watchdog Timer.

Update: I’ve replaced the Win2k machine with a slightly less ancient machine running XP. We’ll see if that improves reliability. I know, reliability and Windows are rarely used in the same sentence. If only I knew someone with realtime OS experience like QNX…

As mentioned during the introduction, these graphs can be very useful in determining what time of the day propagation is open to various parts of the world on certain bands. It is important to remember that much like the weather, propagation changes from day to day, and with the seasons. The levels of solar activity, as well as the effects of solar flares, have a dramatic effect on propagation. Changes in the season affect the number of hours per day of sunlight on the ionosphere over the different parts of the Earth, and cause seasonal changes to propagation patterns.

Do you have a suggestion for a frequency to monitor? Ideally, the frequency should have a station that is on 24 hours a day. If so, please pass it along!

The Effects of a Solar Flare on CHU Reception

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Here’s a graph of the signal strength of CHU 7850 kHz (the Canadian time station) recorded from 2200 UTC on January 18, 2012 to 0100 UTC on January 20, 2012, the signal strength is the pink line, and is in dBm. Also shown on the graph is the solar x-ray flux level, as measured by the GOES 15 weather satellite (click on the graph for a larger image):
CHU 7850 Signal Graph

The recording was made with an SDR-14 set to record a 5 kHz bandwidth (8137 Hz sampling rate) centered on 7850 kHz. This was AM demodulated with the IF filter set to cover 7849.7 to 7852.5 kHz, covering the carrier as well as much of the modulated signal. CHU transmits a carrier and upper side band, with 10 kW of power. The displayed dBm readings are too high by 24 dB, due to the IF gain setting on the SDR-14. I’ll need to correct for that with future recordings. But the relative changes are valid.

We can observe a few things here. First, there are three sudden changes in signal strength:

At 0114 UTC, the signal suddenly dropped by about 25 dB, this is when the band went long. It then further dropped another 6 dB or so.

At 1312 UTC, the signal suddenly came back up, this is when F layer ionization was strong enough again for reception of CHU via NVIS.

At 0038 UTC, the signal dropped again when the band went long. Note that this occurred at a different time than the night before.

For reference, CHU is about 550 km from my location.

The big event on the 19th was the solar flare. It peaked at a level of M3.2, and was a very long duration flare, it stayed at M levels from about 1500 to 1930 UTC. You can see the effects on CHU, the signal dropped about 2 S units (12 dB). The effects on CHU’s 90 meter frequency of 3330 kHz were even more dramatic, I tried tuning in, and it was completely gone. Normally it is S9 or better during the daytime in the winter.

The attenuation was due to the x-rays from the flare increasing the ionization of the D layer of the ionosphere. The D layer does not contribute to propagation, rather it attenuates radio waves. So a stronger D layer means weaker signals, and the effect is more pronounced at lower frequencies.

You’ll notice a dip in the signal around 2300 UTC on the first day, and a small solar flare about the same time. I believe this is a coincidence, not due to the flare. The decrease in signal is too sudden, and the flare was not that large. I quickly put up a special dipole for this test, and it may have some issues. We had some wind that day, perhaps there was an intermittent contact.

While we didn’t have any flares overnight, if we had, there would not have been an affect on the signal, as they only affect the part of the Earth in sunlight, and this path was entirely in the dark side of the Earth.

Propagation Tools – Monitoring Background X-Ray Flux Levels

The GOES 15 weather satellite (the one that is in geostationary orbit and provides the animated views of the weather over the US that you often see on the TV news) also has a set of sensors that monitor the Sun. One of these measures the x-ray output.

These x-rays are produced by sunspots, as well as by solar flares. The x-ray flux we’re interested in is measured in the 1 to 8 Angstrom range (that is the wavelength) and is the red line on the graph below (the blue line is the 0.5 to 4 Angstrom range, x-rays of a shorter wavelength):
x-ray flux

The URL for this graph is http://www.swpc.noaa.gov/rt_plots/Xray.gif

In addition, there is a graph that updates at a 1 minute rate, located at http://www.swpc.noaa.gov/rt_plots/Xray_1m.gif

x-ray flux 1 minute

X-ray level measurements consist of a letter and number, such as B6.7, representing the x-ray flux in watts/square meter. It is a log scale, much like what is used for earthquakes. A value of C1.0 is ten times as large as B1.0 (and would be equivalent to B10). Values in the A range are low background levels, such as at solar minimum. B values are a moderate background, and C values are either a high background or solar flare conditions. Flares usually result in short bursts of large x-ray levels, in the C, M, or even X range. Remember that this is a log scale, so an M1 flare is 10 times as energetic as a C1 flare, and an X1 flare is 100 times. There is a new Y classification as well, so a flare that would have been say X28 in the past would now be Y2.8.

These x-rays ionize the D layer of the ionosphere, which attenuates radio waves. So high x-ray flux levels increase attenuation of radio waves, especially at lower frequencies. Below is a map of D layer absorption:

The x-rays also increase the ionization of the F layer (which is the layer that gives us shortwave propagation), although the effect is less than for the D layer.

The net result is that increased x-ray levels cause more attenuation at lower frequencies, but can also lead to better propagation at higher frequencies. Long periods of high x-ray flux levels (well into the C range) may be a sign of good 10 and 6 meter band conditions. I’ve also found that high (C range) levels seem to “stir the pot” for MW DX, bringing in different stations than usual.

Very high flux levels, such as during a major flare (in the high M or X range) however cause radio blackouts. These occur first as lower frequencies, and as the D layer begins to get more ionized higher frequencies are also affected. Extremely energetic flares (X range) can wipe out all of HF. Note that this is only true for propagation paths on the sunlight side of the Earth. The dark side is not affected. This means that flares can be useful at times, in that they can cause the fadeout of an interfering dominant station on a particular frequency, allowing another station to be heard, providing the geometry of the Earth and Sun are correct such that the path of the interfering station is in the sunlit part of the Earth, while the other station is not.

Solar flares are usually of a short duration, minutes to an hour, although there are “long duration events” that can last for several hours. If you notice suddenly poor conditions, you may want to check the current x-ray flux levels, to see if a flare is the cause. If so, try higher frequencies, as they are less affected.

As we are finally nearing the maximum of Solar Cycle 24 (although it appears it will be a fairly weak maximum) we can expect to see more flares. It can be very handy to continuously monitor the x-ray flux and D layer absorption levels, to see what the current conditions are, and to take advantage of them. One handy way to do this is with DX Toolbox. With DX Toolbox, you can monitor the current conditions, and even get an alert when the x-ray flux exceeds a predetermined alarm value. Some screenshots are below, click on them for a larger image:

DX Toolbox is available for Windows and the Macintosh, you can download a copy at this URL: http://www.blackcatsystems.com/download/dxtoolbox.html

There is also an iOS version available for the iPhone, iPad, and iPod:

Visit this URL for more information:http://www.blackcatsystems.com/iphone/dx_toolbox.html or go directly to the iTunes Store

DX Toolbox also has several propagation prediction windows, to help estimate signal levels for any path you enter, based on solar conditions.

A Day In The Life of 1470 kHz

This waterfall was recorded from 1840 UTC January 3, 2011 to 1840 UTC January 4, 2011. The beginning of the recording is at the top of the image. It shows the carriers of MW radio stations on 1470 kHz. The width is 100 Hz, so frequencies +/-50 Hz from 1470 kHz are shown.

Click on it to open it full sized.

1470 kHz Waterfall

The red line you see in the center is the carrier of semi-local station WTTR. During the daytime it is the only audible station on 1470, although you can see that carriers for about 8 other stations are always present.

I’ve annotated several events with UTC times.

At about 2213 UTC you can see a sudden reduction in received signal strength, and the start of a drift in frequency. This is most likely due to a station switching to nighttime power levels. The change in transmitter power causes a change in temperature inside the transmitter, causing drift in the frequency. My suspicion is that it is WLOA from Farrel, PA, since they are supposed to switch at 2215 UTC.

At about 2252 UTC a carrier suddenly disappears. It is possible that this is KMAL from Malden, MO. They are supposed to shut down at 2300 UTC.

Note that these are hunches of mine, I am not 100% certain that these are the identified stations. These events do suggest that it may be possible to identify and DX stations based on carrier transients, if the actual times that the stations make the changes are known.

At 0400 UTC a carrier suddenly disappears. I am not sure who this could be. This would be 11 PM EST. The station started to fade in around 2300 UTC (6 PM EST). That suggests to me a station in the central US. I’m not sure why they would be shutting down at this late time of the evening, vs around sunset. Perhaps some more experienced MW DXers have some theories / candidates?

There’s also some transients in the morning.

First at around 1200 UTC (7 AM local time) you can see the received signal strengths of the distant carriers decrease. The Sun is rising, and the D Layer is forming again, attenuating MW skywave signals.

At 1230 UTC one of the carriers suddenly disappears. At 1251 a carrier appears.

At 1326, it looks like a a transmitter is changing power levels.

At 1406 UTC there is another transient on another carrier.

There’s also noticeable differences in the frequency regulation of transmitter carriers. Several of the carriers have a periodic cycling to the frequency. I thought is this is due to some temperature cycling in the transmitter.

The 1610 Zoo

Below is a waterfall centered around 1610 kHz in the extended MW (AM) Band, 100 Hz Wide (click on it to see an enlarged image): 1610 waterfall

1610 kHz is used by only two broadcast stations, both in Canada: CJWI in Montreal, and CHHA in Toronto. It is also, however, used by many TIS (Travelers Information Stations) stations, which broadcast traffic reports, weather, etc. These are low power stations, typically in the 10 watt range.

Locally, the dominant station on 1610 kHz is a TIS that relays NOAA weather transmissions, and is located somewhere in south central PA. I’ve never heard an ID.

This recording was made between about 2100 and 1700 UTC, you can see the increase in signal (and background) levels overnight, and then the weakening of the signals as the Sun rises and the D Layer reforms, attenuating distant stations. Looking at the waterfall, you can see dozens of carriers, each a different radio station. It’s interesting to note how many radio station signals are present, even during the daytime.

The horizontal lines are due to static bursts, and there’s some changes in the signal level due to the wind blowing around the antenna.

Some of the wandering of carriers you see that is in unison is due to drift of the A/D clock in the SDR. Other drift you see is due to the carriers themselves. Note that each major division at the top of the waterfall is only 10 Hz (and the entire width is 100 Hz) so there’s really only a few Hz total drift. Eventually I’ll get a more stable reference clock for the SDR, and receiver drift should go away.

Let’s have a contest. How many carriers can you count?