Just what is bentonite?

 and why do I need it?

The ‘OTC Report’ (in the September-October Communicator at https://bit.ly/SARC21SepOct) mentions bentonite as an aid to achieve better RF grounding… but what exactly is this stuff?

In geology, the term bentonite is applied to a type of claystone composed mostly of montmorillonite. It forms by devitrification of volcanic ash or tuff, typically in a marine environment. This results in a very soft, porous rock that may contain residual crystals of more resistant minerals, and which feels soapy or greasy to the touch. However, in commerce, the term bentonite is used more generally to refer to any swelling clay composed mostly of smectite clay minerals.

Sodium bentonite expands when wet, absorbing as much as several times its dry mass in water. Because of its excellent colloidal properties, it is often used in drilling mud for oil and gas wells and boreholes for geotechnical and environmental investigations. The property of swelling also makes sodium bentonite useful as a sealant, since it provides a self-sealing, low permeability barrier. It is used to line the base of landfills, for example. bentonite is part of the backfill material used for waste isolation. Various surface modifications to sodium bentonite improve sealing performance in geo-environmental applications, for example, the addition of polymers.

Here in BC, bentonite was installed in slurry walls in North Vancouver, Quesnel and Williams Lake to stop the migration of railway diesel contamination to adjoining properties.  It was also used it to seal up abandoned environmental monitoring wells, and is  used as pond liner to stop the water from seeping away.

Sodium bentonite can be combined with sulfur as fertilizer prills. These permit slow oxidation of the sulfur to sulfate, an important plant nutrient, and maintain sulfate levels in rainfall-leached soil longer than either pure powdered sulfur or gypsum. Sulfur/bentonite pads with added organic fertilizers have been used for organic farming.

The main uses of bentonite are in drilling mud and as a binder, purifier, absorbent, and carrier for fertilizers or pesticides. As of around 1990, almost half of the US production of bentonite was used as drilling mud. Minor uses include filler, sealant, and catalyst in petroleum refining. Calcium bentonite is sometimes marketed as fuller's earth, whose uses overlap with those of other forms of bentonite.

Bentonite is used in a variety of pet care items such as cat litter to absorb pet waste. It is also used to absorb oils and grease.

What you should know when using ground enhancement material

Under almost all soil conditions, the use of a ground enhancement material will improve grounding effectiveness. Some are permanent and require no maintenance. You can use them in areas of poor conductivity, such as rocky ground, mountaintops and sandy soil, where you can't drive ground rods or where limited space makes adequate grounding difficult with conventional methods.

Bentonite is used to lower the resistance to earth by providing ground enhancement effectively reducing the resistance between the soil and earth electrode (such as copper earth rod or earth mats) by retaining moisture. This inherent ability to absorb and retain rainwater increases the electrical conductivity of the earthing compound in positive correlation to local climatic conditions, specifically average rainfall levels. Typically, the compound has a 3 ohms.m resistivity level – Bentonite compound is a cost-efficient material for backfill of earth electrodes and improving performance when it is physically impossible to drive the earth rods deeper and where challenging ground conditions exist such as rock, granite, etc.

Chemical treatment or backfilling of the soil in close proximity to the location of an underground earthing electrode is an established and traditional method of lowering ground resistance for substation earthing on high resistivity ground – such soil backfilling for electrical grounding improvements is commonly used.

There are several kinds of ground enhancement material available. But use care when choosing the material. It should be compatible with the ground rod, conductor, and connection material. Some options include bentonite clay, coke powder, and specially engineered substances.

Conduction in bentonite clay only takes place via the movement of ions. Ionic conduction can only occur in a solution, which means the bentonite clay must be moist to provide the required resistance levels. When bentonite clay loses moisture, its resistivity increases and volume decreases. This shrinkage results in a discontinuity in the contact between the bentonite clay and surrounding soil, which further increases system resistance.

A noncorrosive low-resistance enhancement substance is a conductive cement that you can install wet or dry. Depending on the substance, it will not leach into the soil and meets EPA requirements for landfill. The railroad and utility industries have successfully used this material. When installed dry, it absorbs moisture from surrounding soil and hardens, retaining moisture within its structure. When used dry, no mixing is required, and you achieve maximum efficiency in a matter of days. This is because it absorbs enough water from the surrounding soil. You can also premix it with water to a heavy slurry. You can add this to the trench containing the grounding conductor or use it around a ground rod in an augered hole. The material binds the water into a cement making a permanent, highly conductive mass.

Some products offer a test-proven resistivity of 0.12 ohm-m or lower, compared with 2.5 ohm-m for bentonite clay. Unlike bentonite clay, the cement-like material does not depend on the continuous presence of water; nor does it require periodic charging treatments or replacement.

An ideal ground enhancement material should not require maintenance. When designing or installing a buried grounding system, look for materials that do not dissolve or decompose over time, require periodic charging treatments or replacements, or depend on the continuous presence of water to maintain conductivity.

~ Internet sources including:

https://www.powerandcables.com/product/earth-tapes-rods-bars-copper/bentonite/ and https://youtu.be/hHtIYboE8NE

 

Why is a 5/8-wavelength vertical antenna better than a 1/4-wavelength

Back to Basics

This 'Back to Basics' may be of particular interests to you off-roaders...

The Canadian Basic Question Banks asks:

B-006-10-4  Why is a 5/8-wavelength vertical antenna better than a 1/4-wavelength vertical antenna for VHF or UHF mobile operations?

A. A 5/8-wavelength antenna has less corona loss
B. A 5/8-wavelength antenna has more gain
C. 5/8-wavelength antenna is easier to install on a car
D. A 5/8-wavelength antenna can handle more power

An ordinary 1/4 λ (wavelength) vertical is smaller and resonant without any loading coil or matching network. What's the advantage to a 5/8 wavelength vertical? Why 5/8 in particular, and not something longer or shorter?

Indeed, why? A 5/8λ isn't resonant where a 1/4λ or 1/2λ would be.

The reason is the radiation pattern. The pattern for a 1/4λ monopole is essentially a doughnut, a pretty good pattern especially for a VHF antenna used primarily for local work. Extending the antenna changes the current distribution. This flattens out the pattern, removing power from the useless (for VHF purposes) vertical dimension and giving more horizontal gain and at a lower angle. See the illustration lower left from the late L. Cebik. The 5/8λ antenna focuses energy somewhat better towards the horizon (lower radiation angle) than a regular quarter-wave antenna.

Depending on the source, they will quote anywhere from 1 dB to 3 dB gain over the 1/2λ design [3dB is a doubling!]. There has also been some discussion that in some areas (urban and mountainous terrain) the lower angle of radiation is a detriment and a standard 1/4λ or 1/2λ antenna is to be favoured. 

So, why 5/8λ? Why not long longer? After all more gain is better right? Well, inspecting the figure below, you will notice the appearance of high angle lobes. As you lengthen the antenna past 5/8λ these lobes become more pronounced and break up the pattern in undesirable ways. Making it shorter maintains a good pattern, but the gain is less. So, 5/8λ is about optimal for this style of antenna.

You may have noticed a pattern developing here. A quarter wave ground plane antenna has a radiation pattern that produces maximum gain at about 25 degrees and a half wave antenna drops that angle to 20 degrees, and the 5/8 wave antenna further drops that angle to 16 degrees. So why not just keep extending the antenna out to one full wave? Well it would be nice if it worked but unfortunately the wave pattern begins to create very high angles of radiation beyond 5/8λ. 

So we've reached the maximum gain at this point and extending the antenna any further just reduces the gain where we want it (low angles). Of course if you are interested in very short skip, extending the antenna will produce nice gains over a dipole. 
All antenna lengths depend on various factors. Some of these factors are: 

• the height above ground;
• the diameter of the wire;
• nearby structures;
• the effects of other antennas in the area; and
• even the conductivity of the soil. 

If we calculate the length of a 5/8λ antenna for our SARC repeater (147.360 MHz) the formula is 178.308/147.36 which equals 1.21m (3.97 feet).

The answer to our question therefore is 2. A 5/8-wavelength antenna has more gain.

Our next Basic Course starts September 15th.

~ John VE7TI
   08-03

Near Vertical Incident Skywave (NVIS) Antennas

HF emergency communications or otherwise, contact stations within the skip zone.

A previous post details Robert VA7FMR’s experiences with a dipole using Hamsticks and a dual bracket. Here is additional information on them and Near Incident Vertical Skywave (NVIS) antennas using Hamsticks. 

SEPAR and many like organizations may be called upon in an emergency to provide ancillary communications for emergency services or primary communications for those emergency service partners who do not have RF communications systems of their own, ESS, The Red Cross and Salvation Army, to name just a few. It is a given that the first stations will be on the higher bands above 50 MHz. Anyone with a Basic License may operate within that spectrum. This should provide reliable communications with modest antennas within the Lower Mainland—no, not just with a handheld and a rubber duckie. Even if many of the local repeaters fail, we should manage to set up a decent network within a few minutes to hours. But what if reliable communications are required for longer distances, for example  to Kamloops or to Seattle, or beyond? VHF and above may not be able to span that distance without gain antennas, placed high with at least 50 Watts of power. HF will be the ‘goto’ bands. We may not need a 60 foot or higher tower to communicate effectively either—this is where NVIS becomes an important emergency communications antenna, especially in the field.

If you recall the antenna theory that you should have picked up in your Basic course, you know that the orientation (horizontal, vertical or somewhere in between) of an antenna will affect its radiation pattern. Much like bouncing a ball off a wall. The greater the angle, the greater the distance the ball bounces away from you. Throw it straight at the wall and it should come pretty close to you on its way back. The same general idea applies to the NVIS antenna. If we cause the RF wave to travel nearly straight up or at a slight angle, it will reflect off the ionospheric layers and come back close to our point of origin. So, if we want to communicate on HF with stations within about 1,500 Kms, we use an antenna that radiates primarily straight up. A DXer on the other hand prefers to talk to stations far away, with a few hops, the farther the better, so DX antennas radiate at angles primarily horizontally to bounce and skip back off the ionosphere for the greatest distance. 

So, the NVIS antenna is one that provides the majority of its radiation at an extremely high angle. That is to say the major lobe is between 75 and 90 degrees to the earth's surface. This will provide excellent omni-directional communication out to a distance of up to about 1,500 Kms with no skip. The maximum frequencies involved will be as low as 1.8 MHz under very poor conditions to as high as 14 MHz under excellent conditions, with the most usable being between 3.5 MHz (80M) and 7.3 MHz (40M).

To summarize, NVIS works for frequencies lower than the vertical incident critical frequency—the highest frequency for which signals transmitted vertically are reflected back down by the ionosphere.  At or below the critical frequency the ionosphere will reflect an incident signal arriving from any angle, including straight up. Because the critical frequency is low, you must usually operate 40, 80 or 160 meters or possibly 30 meters to use NVIS propagation.

Under most conditions you can easily obtain coverage on one of these bands from zero to 350 miles or more with no skip zones. On 75 meters with 100 W and an antenna 15 feet high, contacts with stations over 1000 miles away with excellent signal reports are not uncommon. 

These are the characteristics we look for in an emergency-ready HF antenna for distances up to about 1,000 miles… No skip, easy set-up and take down and reasonably reliable communications.

When I first started looking at the NVIS antenna for "local", primarily emergency communications, the consensus seemed to be that it was a dipole-type antenna, near 1/8th wave at the operating frequency, above the ground. I purchased a set of HamSticks, mounted as a dipole, for this purpose as I was operating from a vacation area surrounded by high mountains.  NVIS antennas are commonly used by the military, as their needs fit these characteristics. There is an excellent, though technical article at https://region6armymars.org/downloads/NVIS-Antenna-Theory-and-Design.pdf

Every horizontal antenna has an NVIS component in its radiation. Similarly, every horizontal antenna has a component that is most useful for DX. Your decision then is to pick the configuration that either favours or optimizes the properties you want.  Reliable local communication on HF dictates NVIS. How then do we determine what NVIS antenna will best suit our needs?  Let’s examine the parameters that have a significant effect in antenna performance. This is information on how to make it work reasonably well, NOT a graduate degree treatise on the theory of NVIS.

Height above ground

The antenna height above ground seems to be the single most controversial subject in discussion of NVIS antennas. Some say anything below 1/4 wave works. Others say anything below 1/8th wave and yet others say ten to fifteen feet works very well. You will note that there is negligible difference in antenna gain between 1/8 wave and 1/4 wave height. There is however a significant difference in the logistics of placing an antenna at 70 some feet in the air versus 35 feet in the air.

Antenna guru L.B. Cebik (W4RNL), writing about NVIS antenna elevation, explains that the height, in the 1/8 to 1/4 wave length above ground, has very little difference in gain. In fact, if you roll in the next parameter, ground (detailed below), height can easily have much less effect than ground.

The Near Vertical Incident Skywave (NVIS) antenna is a half-wave dipole antenna, configured straight or as an inverted vee, mounted not over 1/8th wave above ground (at the highest operating frequency). While 1/8th wave works reasonably well, better coverage is obtained if the antenna is mounted at about 1/20th wavelength above ground. A second advantage of lowering the antenna to near 1/20th wavelength is a lowering of the background noise level. At a recent ARRL Section Emergency Test, communication on 75 Meters was started with a dipole at approximately 30 feet. They found communication with some of the other participants to be difficult. A second 1/2 wave dipole was built and mounted at 8 feet off of the ground. The background noise level went from S7 to S3 and communications with stations in the twenty-five and over mile range were greatly enhanced. Simply stated, you want as much of your signal going up as possible and ten to fifteen foot height has shown to function very well. It was also found that a network of stations, all using NVIS antennas experienced much stronger local signals.

Ground

Yet another consideration is the "quality" of the ground below your antenna. By this we mean the conductivity of the ground you are operating above. For any given height (1/4th wave length or less) poor conductivity will attenuate up to 3db more of your signal than high conductivity soil. A documented example is the ARES installation in Longmont, CO at the Emergency Operations Center. That antenna is mounted ten feet above a flat roof. The base for the roof is a grounded steel plate. This antenna consistently performs as well or better than any other in the state. The reason is simple; A full sized resonant dipole antenna mounted ten feet above an excellent ground.

A specific example of how well the Longmont EOC antenna works is one Sunday when testing the antenna, a local ham tried his Yaesu FT-817 running on the internal battery pack. As most know, that configuration produces 2.5 watts PEP maximum output. At that power level he received a signal report from NCS in Colorado Springs (90 miles South) of S9+10db, on 75M just before the net started.

Another example of how the conductivity affects your signals comes from Colorado where they regularly use NVIS antennas on 60M to communicate across the Continental Divide. Doing this on a twice weekly basis for several years now they have established a base-line for comparison. The week of 23 September 2004 they had a slow moving rain storm that put down more than one inch of rain, spread almost evenly over about 36 hours. For those that have thirty to fifty inches of rain per year, that would not be much. In Colorado that is one-fifteenth of their total annual precipitation. After the rain, under less than optimal band conditions, signals were UP 6 to 10db!

The chart by L.B. Cebik's (W4RNL) shows that any NVIS, above excellent ground, out performs an antenna above good ground at optimal height! Hmmm, does that imply that we have found the single most important parameter in NVIS?

Ground wire

Yet another approach is to run a "ground" wire at the surface where the antenna is mounted. A good discussion on this is found at an Australian site by Ralph Holland. He did some research on 160M and found that a ground wire at .02 to .06 wave lengths below the driven element produced the best gain. That translates to about 5 to 15 feet at 75M which would be consistent with the heights seen that have  produced the best NVIS performance. Others claim at least a 6db improvement with this same approach.

Experimenters  also notice an improvement if  you "water" the ground just prior to operation. Pour about one gallon of water on the ground around the ground rod or wire. If it seeps in very quickly, go get another gallon. This has made a noticeable improvement in both transmit and receive signals. 

Counterpoises

The high angle radiation of a dipole (or inverted vee) can be enhanced by adding a counterpoise wire below it, about 5% longer than the main radiating element, to act as a reflector. The optimum height for such a counterpoise is about .15 wavelengths below the main radiating element, but when the antenna is too low to allow for that, a counterpoise laid on the ground below the antenna is still effective.

A knife switch at the center point of the counterpoise can be used to effectively eliminate the counterpoise from the antenna system. This technique is useful for using a dipole for NVIS and longer distances, too. A counterpoise is installed at ground level, or as high as the switch can easily be reached, and a dipole is mounted .15 wavelengths above the counterpoise. When the switch is closed, the vertical gain will increase, and the noise levels will drop. When the switch is open, lower angle gain will increase, improving the antenna's performance for non-NVIS use.

Dual Ham-Stick

This is a portable antenna on a 5-foot mast that does well under ARES/RACES operating conditions. One person can put this up and have it operational in under five minutes! A side advantage of this antenna is its comparatively small size. It is only sixteen feet in length, which makes it much more reasonable for temporary installations.

‘HamStick’ antennas may be paired to make a very usable dipole antenna.
Mounting height will affect  the radiation pattern and therefore propagation.

Above, a typical HamStick and adjustable whip and the dual mount that makes it a dipole with directivity

. 

Inverted Vee

A dipole's close cousin, the inverted vee, is another good NVIS antenna which can be even simpler to support. An inverted vee will work almost as well as a dipole suspended from a slightly lower height than the apex of the inverted vee, so long as the apex angle is kept gentle—about 120 degrees or greater. An inverted vee is often easier to erect than a dipole, since it requires only one support above ground level, in the center.

This design has been successful for the author. It was developed by Dr. Jelinek and is in commercial use by the Armed Forces.

How do I select a frequency for NVIS operation?

The selection of a optimum frequency for NVIS operation depends upon many variables. Among the many variables are time of day, time of year, sunspot activity, type of antenna used, atmospheric noise, and atmospheric absorption. To select a frequency to try, one may use recent experience on the air, trial and error (with some sort of coordination scheme agreed upon in advance), propagation prediction software like VOACAP, near real-time propagation charts (available on the Internet) showing current critical frequency, or even just a good educated guess. Whatever the strategy used for frequency selection, it would probably be best to be prepared with some sort of "Plan B" involving communicating through alternate channels, or following some pre-arranged scheme for trying all available frequency choices in a scheduled pattern of some sort.

http://webclass.org/k5ijb/antennas/NVIS-low-antenna-regional-communications.pdf

A NVIS antenna on a wartime military vehicle.

Finally, this is also an antenna that should be in the ‘kit’ for Field Day or contests. We usually concentrate on working any and all stations however, skip actually works against us when it eliminates many potential contacts up to 1,000 miles or so. The ability to switch to an NVIS antenna will bring in those stations within the skip zone and enhance the score. This strategy has helped us place first in Canada in our 3A Field Day category for several years.

~17/10

Back To Basics: F2 Region 'Hops'

What is the maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?

B007-003-002

A. 2000 km (1250 miles) 
B. 300 km (190 miles) 
C. 4000 km (2500 miles)
D. None, the F2 region does not support radio-wave propagation

There are at least a dozen questions in the Canadian Basic Question Bank that touch on propagation, this is just one of them. The science of RF propagation can take volumes to explain, let’s see if we can summarize the basics.

Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering.
Radio propagation is affected by the daily changes of water vapor in the troposp
here and ionization in the upper atmosphere influenced by the Sun. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for Amateur Radio contacts, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.

Several different types of propagation are used in practical radio transmission systems. Line-of-sight propagation means radio waves which travel in a straight line from the transmitting antenna to the receiving antenna. It does not necessarily require a cleared sight path; at lower frequencies radio waves can pass through building walls and foliage. Line of sight transmission is used in short to medium range radio transmission such as garage door openers, cell phones, cordless phones, walkie-talkies, wireless networks, FM radio and television broadcasting and radar, and satellite communication, such as satellite television. Line-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, about 40 miles. It is the only propagation method possible at microwave frequencies and above. At microwave frequencies moisture in the atmosphere (rain fade) can degrade transmission.

At lower frequencies in the MF, LF, and VLF bands, due to diffraction radio waves, can bend over obstacles like hills, and travel beyond the horizon as surface waves which follow the contour of the Earth. These are called ground waves. AM broadcasting stations use ground waves to cover their listening areas. As the frequency gets lower the attenuation with distance decreases, so very low frequency (VLF) and extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.
At medium wave and shortwave frequencies (MF and HF bands) radio waves can reflect or refract from a layer of charged particles (ions) high in the atmosphere, called the ionosphere. So radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances. This is called skywave or "skip" propagation. It is used by amateur radio operators to talk to other countries, for diplomatic communications, and by international shortwave broadcasting stations. Skywave communication is variable, dependent on conditions in the upper atmosphere, and can be disrupted by events like solar flares, it is most reliable at night and in the winter. Due to its changing nature, since the advent of communication satellites in the 1960s many long range communication needs that previously used skywaves now use satellites.

Solar activity has a cycle of approximately 11 years. During this period, sunspot activity rises to a peak and gradually falls again to a low level. 

An international panel of scientists co-chaired by NOAA and NASA release reports every few months on the state of the sunspot cycle. This is probably the most accurate source in terms of what is likely to happen.

Current Sunspot Cycle 24 gave a smoothed sunspot number maximum of about 69 in the late Summer of 2013. The smoothed sunspot number reached 68.9 in August 2013, the official maximum. Now, at the start of 2020 we should be at or near the bottom and it is hoped things will start to improve. We are currently seven years into Cycle 24. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906.

Back in April of 2019, the previous report predicted that the  solar minimum would likely happen between July 2019 and September 2020. In the most recent report dated December 2019, they are predicting that the minimum has been pushed back. They predict that it will now occur sometime between November 2019 and October 2020.

As for the upcoming Solar Cycle 25, they are still predicting that it will be similar in intensity to the last solar cycle with a smoothed sunspot number (SSN) of 115. The peak is predicted to occur between November 2024 and March 2026.

When sunspot activity increases, the reflecting capabilities of the F1 layer surrounding earth enable high frequency short-wave communications. The highest-reflecting layer, the F2 layer, which is approximately 200 miles (320 km) above earth, receives ultraviolet radiation from the sun, causing ionization of the gases within this layer. During the daytime when sunspot activity is at a maximum, the F2 layer can become intensely ionized due to radiation from the sun. When solar activity is sufficiently high, the MUF (Maximum Usable Frequency) rises, hence the ionization density is sufficient to reflect signals well into the 30 – 50 MHz VHF spectrum. Since the MUF progressively increases, F2 reception on lower frequencies can support potential low band amateur radio paths. A rising MUF will initially affect the 27 MHz CB band, and the amateur 28 MHz 10 meter band before reaching 45-55 MHz TV and the 6 Meter amateur band. The F2 MUF generally increases at a slower rate compared to the Es MUF.

Since the height of the F2 layer is some 200 miles (320 km), it follows that single-hop F2 signals will be received at thousands rather than hundreds of miles. A single-hop F2 signal will usually be around 2,000 miles (3,200 km) minimum. A maximum F2 single-hop can reach up to approximately 2,500 miles (4,000 km). Multi-hop F2 propagation has enabled low-band VHF reception to over 11,000 miles (17,700 km).

The correct answer to our question "What is the maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?" therefore is (C) 4,000 Km (2,500 miles) 

~ John VE7TI

Earth At Night!

A Free NASA eBook 

Earth at Night, NASA’s free new 200-page eBook in three formats, is now available online showing our planet in darkness as captured from space by Earth-observing satellites and astronauts on the International Space Station over the past 25 years.

Aside from the fascinating photos, there are explanations of Earth's weather as well as the Aurora and other phenomena of interest to the Amateur Radio Community

https://www.nasa.gov/connect/ebooks/earthatnight_detail.html

More On Propagation...

Back to Basics

From the Canadian Basic Question Bank

Back To Basics is a regular column in the SARC Communicator Newsletter, available on this blogsite.

B-007-003-002
What is the maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?

A. 2000 km (1250 miles) 
B. 300 km (190 miles) 
C. 4000 km (2500 miles)
D. None, the F2 region does not support radio-wave propagation

There are at least a dozen questions in the Canadian Basic Question Bank that touch on propagation, this is just one of them. The science of RF propagation can take volumes to explain, let’s see if we can summarize the basics.

Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering.

Radio propagation is affected by the daily changes of water vapor in the troposphere and ionization in the upper atmosphere influenced by the Sun. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for Amateur Radio contacts, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.

Several different types of propagation are used in practical radio transmission systems. Line-of-sight propagation means radio waves which travel in a straight line from the transmitting antenna to the receiving antenna. It does not necessarily require a cleared sight path; at lower frequencies radio waves can pass through building walls and foliage. Line of sight transmission is used in short to medium range radio transmission such as garage door openers, cell phones, cordless phones, handheld transceivers, wireless networks, FM radio and television broadcasting and radar, and satellite communication, such as satellite television. Line-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, about 40 miles. It is the only propagation method possible at microwave frequencies and above. At microwave frequencies moisture in the atmosphere (rain fade) can degrade transmission.

At lower frequencies in the MF, LF, and VLF bands, due to diffraction radio waves, can bend over obstacles like hills, and travel beyond the horizon as surface waves which follow the contour of the Earth. These are called ground waves. AM broadcasting stations use ground waves to cover their listening areas. As the frequency gets lower the attenuation with distance decreases, so very low frequency (VLF) and extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.

At medium wave and shortwave frequencies (MF and HF bands) radio waves can reflect or refract from a layer of charged particles (ions) high in the atmosphere, called the ionosphere. So radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances. This is called skywave or "skip" propagation. It is used by amateur radio operators to talk to other countries, for diplomatic communications, and by international shortwave broadcasting stations. Skywave communication is variable, dependent on conditions in the upper atmosphere, and can be disrupted by events like solar flares, it is most reliable at night and in the winter. Due to its changing nature, since the advent of communication satellites in the 1960s many long range communication needs that previously used skywaves now use satellites.

Solar activity has a cycle of approximately 11 years. During this period, sunspot activity rises to a peak and gradually falls again to a low level. 

The current prediction for Sunspot Cycle 24 gave a smoothed sunspot number maximum of about 69 in the late Summer of 2013. The smoothed sunspot number reached 68.9 in August 2013, the official maximum. 

We are currently over 7.5 years into Cycle 24. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906.

When sunspot activity increases, the reflecting capabilities of the F1 layer surrounding earth enable high frequency short-wave communications. The highest-reflecting layer, the F2 layer, which is approximately 200 miles (320 km) above earth, receives ultraviolet radiation from the sun, causing ionization of the gases within this layer. During the daytime when sunspot activity is at a maximum, the F2 layer can become intensely ionized due to radiation from the sun. When solar activity is sufficiently high, the MUF (Maximum Usable Frequency) rises, hence the ionization density is sufficient to reflect signals well into the 30 – 50 MHz VHF spectrum. Since the MUF progressively increases, F2 reception on lower frequencies can support potential low band amateur radio paths. A rising MUF will initially affect the 27 MHz CB band, and the amateur 28 MHz 10 meter band before reaching 45-55 MHz TV and the 6 Meter amateur band. The F2 MUF generally increases at a slower rate compared to the Es MUF.

Since the height of the F2 layer is some 200 miles (320 km), it follows that single-hop F2 signals will be received at thousands rather than hundreds of miles. A single-hop F2 signal will usually be around 2,000 miles (3,200 km) minimum. A maximum F2 single-hop can reach up to approximately 2,500 miles (4,000 km). Multi-hop F2 propagation has enabled low-band VHF reception to over 11,000 miles (17,700 km).

The correct answer to our question therefore is (C) 4,000 Km (2,500 miles) 

~ John VE7TI

Propagation Prediction

It’s All In The Layers

Someone told me they considered the “magic” of ham radio was the radio signal, but in my opinion the magic is really the radio wave skip propagation that allows world-wide communication without satellites.

You have probably heard another amateur operator mention at one time or another something about propagation being “terrible” or just the opposite, it was “excellent”.  What does this all really mean? I want to take a few minutes to revisit radio propagation outside of what can be found in the usual study guides and perhaps pique your interest in researching further on your own.

Depending on the band your using you may not even use any form of “skip” or atmospheric benefits. An example of this would be line of sight or ground waves used by VHF. Typical repeater use will all but bypass what we often think of as radio propagation. It is true that the signals are “propagating” through the air but not necessarily skipping along the atmosphere to the benefit of either sender/receiver. Actual VHF propagation can still occur to our benefit and allow for distant radio communication in the form of tropospheric propagation and ducting.  This is when under just the right weather conditions a sandwich of moist hot air is trapped between two layers of cold dry air.

But how can we visualize VHF/UHF propagation or know when it’s happening? There is a tropospheric forecast available online http://www.dxinfocentre.com/tropo_wam.html  that visually shows predictions like weather charts show us hot and cold fronts and storms. 

A prediction is only as good as the data the science model shows. How can it really be used by a radio operator? By noticing a storm pattern or simply that the conditions are favourable could mean it’s time to experiment.

However to really visualize real time propagation reports on VHF we turn to APRS. Automatic Packet Reporting System is used by a variety of amateur radio operators to report their location and for messaging via packet radio. APRS equipped VHF radios send out beacon packets on a National frequency of 144.39 MHz and these packets include the sender’s GPS location. All APRS receivers are able to read the beacon packets can record the information. Some of the receivers are Internet enabled and catalogue all the beacons to popular websites like https://aprs.fi.  This information can then be used to show real time VHF propagation reports because we know both the sender and receiver’s precise location and can calculate exactly the distance between each station.

An example of this is the website http://aprs.mountainlake.k12.mn.us/ which adds visual aides to show the direction and distances between sites that have recently been heard.

Digital modes are far better at being received at long distances but the theory is that if packet radio is working, then voice will see a benefit as well. The contacts displayed that are yellow or red are a great distance for VHF and not necessarily line of site.  Without much elevation gain 2-way VHF is limited by the curvature of the earth. Only 6 feet above sea level antennas the distance about 3 miles. Most of the time for VHF use, one or more of the transmitters is well above 6 feet and aides in the transmission beyond the curvature of the earth.

The National VHF calling frequency of 146.520 Mhz FM or 144.200 Mhz SSB can be used during times with good VHF propagation and, if conditions are right,  make some very long distant contacts on 2m. The ARRL confirmed in 2015 that the VHF calling frequency could also be used for contests. http://www.arrl.org/news/use-of-146-52-mhz-fm-simplex-frequency-cleared-for-arrl-contests. This means that with the right conditions a contest on VHF could be great fun.

Larry Shaunce WD0AKX in Minnesota produced a video of VHF ducting https://www.youtube.com/watch?v=gBJQ0Ha9ORM

One of the first methods to help measure HF propagation is to listen on WWV. https://www.nist.gov/time-and-frequency-services/nist-radio-stations/wwv. This is a time and frequency checking station located near Fort Collins Colorado. It broadcasts the local time 24/7 up to 10,000 watts of power on 5, 10, 15 Mhz and 2500 watts on 2.5 and 20Mhz. One way of looking at it might be if you can’t hear this station clearly it could indicate issues running QRP or 100 watts on the nearest band. It can also be used simply to test your antenna and rig since it’s a strong signal running 24 hours a day.  http://tf.nist.gov/stations/iform.html

Unrelated to propagation, ARRL has a contest each year that contestants try to measure an exact frequency. FMT (Frequency Measuring Test) can also be used to determine propagation shifts.   WWV can be used as warm up for those wanting to begin entering the FMT contest world.

http://www.arrl.org/frequency-measuring-test

http://www.k5cm.com/

Beyond the use of WWV and FMT  there are the International Beacon Project . This consists of several key locations around the world each in perfect time synchronization. They rotate their signals and every few seconds a different location can be heard. All you must do is park your radio on the nearest band you wish to operate and listen.

The callsign of the station is sent by CW at 100watts, then long dashes after consisting of gradually less power, 10watts, 1watt, 100milliwatts.   You could somewhat predict how well propagation is on the band by listening for key stations in your region. Find it at URL: http://www.ncdxf.org/beacon/

Long term predictors of radio propagation is the use of tracking space weather specifically the sunspot activity. This is an entire subject in of itself that I personally would like to learn more about. 

We are at the bottom after an 11 year cycle of “good” solar activity.

http://www.swpc.noaa.gov/products/solar-cycle-progression 

Recently I came across an article about the idea of the US Air Force wanting to spread plasma bombs in the sky to improve radio communication. Multiple research teams have been contracted to study this and the current thinking is that some form of small targeted plasma bombs in space could be used to improve radio communication. Perhaps some day we will all be looking at the targeted plasma propagation website? 

http://www.dailymail.co.uk/sciencetech/article-3753417/The-Air-Force-reveals-radical-plan-bomb-sky-improve-radio-reception.html

~ Jeremy VE7TMY

Still Puzzled About HF Propagation?

Deciphering a Propagation Report

Richard VE2XIP has an informative blog on a variety of Amateur Radio subjects. Among the areas he covers is a very good primer on HF Propagation. I know this subject can be a difficult one to grasp, especially for beginners—even the more experienced have challenges in this area.

Richard writes: 

“The very first thing I noticed when I got interested in propagation was a vast number of websites displaying charts and grids related to HF propagation conditions, but I didn’t really understand them at first. There are more types of measurements about the Sun’s activities than most care to understand, but there are a few ones that are very important to learn if you want to be able to understand a propagation reports.”

Have a look at the document. It’s at URL: https://www.qsl.net/co8tw/Understanding%20HF%20propagation.pdf

Can Shortwave Radios Detect Earthquakes?

A New Tool To Assist Earthquake Prediction?

The RF Seismograph: Another Exciting Amateur Radio First

Alex Schwarz VE7DXW, presented his findings at the SARC April 2019 monthly general meeting. Alex is exploring the possibility that “RF signatures” detected by the RF Seismograph propagation tool could also be indicating earthquakes, and may even be able to predict them shortly before they occur; one or two hours appear likely. A real-time HF propagation-monitoring tool developed by Schwarz and the MDSR team, the RF Seismograph shows both band noise and activity or band activity alone on six HF bands. It’s a project of the North Shore Amateur Radio Club (NSARC).

It has been documented for some time that major geological movements create magnetic waves. These magnetic waves interact with RF and manifest themselves as disturbances that are received on HF. Alex had been monitoring propagation intending to study the effects of the last solar eclipse. His finding showed a correlation with earthquake activity and the RF Seismograph was born. Basically, this is a broadband HF receiver monitoring a large range of frequencies. 

The RF-Seismograph’s recent discovery that Earthquakes can be detected using a RF-receiver are intriguing and it validates a lot of new research that claims that earthquakes also create a magnetic field that extends into the Ionosphere and causes changes that can be measured with a cluster of GPS receivers.

The RF-Seismograph team has been collaborating with Earthquakes Canada to find a correlation between HF propagation and earthquakes. There was a distinct event that occurred on Nov 1st  (M5.0 off the coast of Vancouver Island) which was detected by the RF-Seismograph an hour before. Of course an hour warning before a major earthquake is significant.  There is process underway to correlate earthquakes that are bigger than M6.0 with the 4 years of data accumulated so far. 

“We had been doing the solar eclipse experiment, and we developed the RF Seismograph software to look for changes in propagation during the eclipse,” Schwarz explained. “After the eclipse, we decided to leave the RF Seismograph running, and we have now collected 4 years of data.”

The system uses an omnidirectional multiband antenna to monitor JT-65 frequencies (±10 kHz) on 80, 40, 30, 20, 15, and 10 meters. Recorders monitor the background noise and display the result in six color-coded, long-duration graphs displaying 6 hours of scans. When signals are present on a band, its graph trace starts to resemble a series of vertical bars.

Most recently, the RF Seismograph recorded the magnitude 7.5 earthquake in Ecuador on February 22. Schwarz recounted that noise on 15 meters began to be visible about 1 hour before the quake; then, 2 hours after the quake released, 15 meters started to recover. The US Geological Survey said the quake was about 82 miles below ground. It did not affect 80 meters. Schwarz speculated that the quake was easy to see on the RF Seismograph because 15 meters typically is not open during hours of darkness — especially when the solar flux is only 70

Following a magnitude 5.0 earthquake off the coast of Vancouver Island, his RF Seismograph picked up changes. Canada’s government-run Earthquakes Canada was able to provide Schwarz with a list of magnitude 6.0 or greater events since the RF Seismograph went into operation, and the two teams have been collaborating to find a correlation between HF propagation anomalies and earthquakes. With the measurements, Schwarz has been attempting find a correlation between the list of past geological events and what his RF Seismograph may have sensed on those occasions.

“The earthquakes show up as RF noise because of the electric field lines, now scientifically confirmed to change the way the ionosphere reflects RF,” Schwarz said. He cited an article in the October 2018 edition of Scientific American, which, he says, “explains it really well.” (See Erik Vance’s “Earthquakes in the sky,” Scientific American, October 2018, p. 44).

The Scientific American article explores measurements in Japan looking into how earthquakes can create electric field lines that extend into the atmosphere. “Could they be used to detect earthquakes before they cause damage on the planet?” Schwarz asks.

Schwarz said 171 earthquakes — all magnitude 6.0 events or greater — were studied, and only 15 of them had no RF noise associated with them. In 26 cases, the time of the disturbance detected by the RF Seismograph failed to match the USGS-reported time of the quake. The latter likely because of the current low solar cycle and poor propagation.

Schwarz said that in 72% of the earthquake studies, the RF Seismograph was able to detect an increase in noise on 80 meters, typically before and after the event.

“More analysis is needed,” Schwarz has concluded. “The study is still continuing and we need your help to set up more monitoring stations.”

RF Seismograph is now a project on Scistarter.com, facilitated through Arizona State University. Schwarz said Scistarter hosts “interesting projects for all ages and backgrounds” and “provides a vehicle for young people that are interested in science to get real live experience in this field.”


Contact Schwarz for additional information.  

A video of Alex's presentation is available at: https://youtu.be/Wz0ZkWXkIow

The presentation slides are at: http://nsarc.ca/wp-content/uploads/2019/04/RF-Seismograph-detects-Earthquakes-Markup.pdf

Alex’s site: http://users.skynet.be/myspace/mdsr/index.html

Partial post content courtesy of http://www.arrl.org/news/ve7dxw-s-rf-seismograph-may-be-real-seismograph