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

Double Your Range! A Counterpoise For Your Hand-held

A Communicator Reprise

September 2015

The counterpoise (sometimes referred to as a ‘Tiger-Tail’) is typically used in antenna systems for radio transmitters where a good earth ground connection cannot be constructed. In this application, it is simply a 19-inch length of common wire attached to the ground of your hand-held transceiver antenna terminal.

In the photo it is attached to a ring terminal with sufficient diameter to fit under the antenna. Alternatively, it can also be stripped of insulation and simply be wrapped around the antenna base, as long as it makes a good electrical contact.

It is very effective in extending the range of a portable transceiver in that it provides the 'missing' half of the dipole antenna for 2m or 70cm operation. In order to keep antennas short and manageable, radio manufacturers coil the antenna wire into a rubber covered spring—half the antenna. The transceiver body is the other half, but is not very effective from an RF perspective. Those little rubber antennas can have a very high SWR, power reflected back to your radio rather than radiating out. The counterpoise, left hanging straight down beside the radio on receive and transmit provides a much more efficient solution.

Try it with a weak station, you’ll surely notice the difference.

~ John VE7TI

The Power Gate: Keeping The Voltage On

A Communicator Reprise...

 November 2015

The commercial alternatives are good, but pricey. Here is an option for less than $10

In the September and October 2015 issues of the SARC Communicator [and on this blog], we featured circuits that will provide you with a reliable, robust power source. In September 2015 it was Hiu Yee VE7YXG’s simple Gel-Cell Battery Charger, and in October 2015 John Brodie VA7XB’s low cost Battery Monitor Project. This time we’ll round out this series with a device that will automatically switch your station to battery power if the AC fails, and switch it back when the power comes on. It is both inexpensive and simple, yet reliable, as there is only one part.

First, lets look at the commercial alternatives. There are a number of solutions on the market including one, quite expensive, at US$140, known as the West Mountain PwrGate. This device uses solid state devices to charge and automatically insert a backup battery if there is a power outage, and to switch back to the power supply if it is restored.

You will note that the PwrGate above is housed in a large heat sink. This device used Schottky diodes which can generate significant heat. Those fins are there to dissipate that heat. Heat is wasted energy, so we look at an alternative device that is more efficient.

The low-loss PWRGate is billed as being simple, safe, and reliable, and easily able to add backup battery power to your home station or go-kit. The Low Loss PWRgate uses MOSFET power transistors to switch the load between power sources with less than a 20 miliVolt drop, much smaller than systems that use Schottky diodes.  This keeps the power losses to a minimum and delivers full battery power to the load. The device is rated at 25 Amp total, with 3 power outlet ports, ARES standard Anderson Pole Connectors, 3 ozs, and US$49.95 plus shipping by USPS Priority mail. Note that there is no heat sink here, and it does not charge the battery. The distributor, Flint Hills Radio Inc. will also sell you a solar battery charge controller for US$ 39.95 plus shipping and a Smart Lead-Acid Battery Monitor and alarm for another US$ 29.95 plus shipping.

Makes our projects seem pretty reasonable doesn’t it?

So back to the low cost alternative. This device transfers up to 40 amperes at up to 14 volts DC continuously.  It is a safe way to connect both a 12 volt battery and a 13.8 volt power supply to a load, while electrically isolating both from each other.  Whenever your power supply is on, the supply feeds the load, and if you add Hiu’s charger, will also charge the battery, keeping it healthy and ready for use when the power supply is off, or loses AC power, all at a cost of about CA$ 10.00

I did some time in the seventies as a service technician while in my early twenties. One of the products I had some exposure to was alarm systems. In those days before PWRgate, a simple single pole double throw (SPDT) relay was used for the same purpose. The relay is the same as used in many automotive systems. In this application, if the magnetic relay coil is activated, when normal power is on, the contacts switch in the power supply. If the power supply loses voltage, as in a power failure, the magnetic coil is no longer activated and releases the contacts, which then switch in the battery backup. The coil, now deactivated does not rob the battery of any current. A very simple solution with no loss through excessive circuitry or heat. The coil uses a bit of current from the power supply to remain activated, but this is minimal.

These relays are commonly available at auto supply dealers but I ordered mine through eBay and received two, with sockets and mounting brackets, for US$ 3 shipped. They are rated for 12-14 Volts DC and 40 Amps, more than enough to handle the current that most transceivers would draw. Wiring is fairly straight forward and I used three sets of Anderson PowerPole connectors. One for the battery, one for the power supply and one set for the load, being my transceiver. A numbered connection diagram was stamped on the top of the relay I received. The relay coil is wired in parallel with the power supply. If the power supply is on, the relay keeps it feeding the supply circuit. If the power supply goes off current is diverted from the battery.

Once I figured out the contact layout, the actual construction took me only about half an hour, definitely something that can be tackled even by a beginner. Pair this with Hiu’s charger and John’s low voltage alarm and you’re good to go uninterrupted if the power goes out.

~  John VE7TI

HF Antennas In A Restricted Space

A Communicator Reprise

June 2016

I want to share my experience with those of you who have recently passed their test and are looking for that perfect HF antenna that will suit their “New Shack” at their home location. My thoughts were focused on an antenna that would cover as many of the Ham bands as possible, that could be hidden on my apartment patio deck. I did, as most of you will, a lot of reading on the subject and eventually chose a Current Loop Antenna that was the rave in the UK and it set me back about $350 with shipping and tax. I set it up on my patio and I started to tune through the Ham bands and hardly heard a thing, I mean that, apart from static and a couple of stations, one in Alaska talking to a fellow in California, I heard nothing. I was beginning to think that there was something wrong with my radio, a brand new Icom 7100 and John Brodie very kindly invited me to his home and we attached my radio to his antenna. The radio immediately jumped to life with more stations than I could count. I tried several CQ calls and was rewarded with a reply from South Carolina some 2600 miles away, on 70 watts. What a thrill that was. Now knowing that my radio was in perfect shape, I again started to search for the perfect antenna.

Having proved that my radio was fine, I took the current loop antenna apart and put it where the proverbial squirrel stores his winter supplies and started looking for another antenna. I found an antenna called “The Tarheel Antenna” this is a motorized multi band antenna with excellent ratings, it is a mobile Antenna that I could mount to my patio railing and also mount it on my vehicle for away from home outings. Well, although I could hear more stations compared to the Current loop, they were so far below the noise level that they were not useful at all. Having spent another $700 plus on the Tarheel I still did not have a working antenna. All of the successful Hams will tell you that your success is based on Antenna, Antenna, Antenna.

I have reached the conclusion that my location is in a null zone created by the apartment blocks in which I live. The HF Spectrum is a fickle thing sent to try us. Imagine, if you will, a letter L reversed, the bottom leg runs North South and the vertical leg runs East West, the vertical leg being south of the bottom leg. I live on the East side of the bottom leg on the second floor, rite in the corner created by the bottom leg and the vertical leg. My location is protected by both of the apartment blocks.

My mistake was trying to buy the antenna that would cover the most HAM bands as possible, right up front, before checking to see if there were any signals at all. My advise to you and the whole reason for this small article, is to choose an antenna that covers one band, lets say the 20 meter band. Try to buy the cheapest antenna you can find, within reason, try to stay away from the Chinese antennas, they are usually of very poor quality. 

Put up the antenna at night if you are like me and live in an apartment, if you live in a house you will have a lot more room to play with than apartment dwellers. If you can hear contacts that are well above the noise level, have fun and start to build your log book. If like me, you hear little or nothing, you have just saved yourself a ton of money. Buying antennas can be very expensive as I have found to my sorrow.

I have not, however given up. There are lots of opportunities as a mobile station with my Tarheel antenna and setting up, as in the Field Day event, in a park with a long wire antenna. In my opinion, the whole idea of being a HAM is to have as much fun as possible with what you have and I certainly intend to do so.

~ Robert VA7FMR


Since this article was published, Robert has solved his apartment antenna issues. Check out the November-December 2019 issue of 'The Communicator for his solution. It will be posted here November 1st. - Ed.

Two Battery Monitor Projects

A Communicator Reprise...

October 2015

John demonstrating his meter to the group

Last spring, SARC initiated a competition to see who could construct the most suitable and innovative 12 volt battery monitor for use at Field Day.  Here is what I came up with.

  

The following design criteria were used for my version of the monitor: a) it should provide an analog reading of voltage, accurate to 0.1 volt; b) it should have an alarm that would warn of critical low voltage at an adjustable level; c) the alarm should be prominent but not disruptive to other operators; and d) it should be cheap and easy to build.  Anderson power poles would be the connector of choice.
  
I prefer an analog display as it is easier to discern conditions at a glance without having to read a series of digits on a digital display which may be fluctuating rapidly.

The monitor was constructed around a low voltage FK915 alarm kit purchased on line for US$ 5.95 from www.Qkits.com.  

For the voltage indicator, I found an old analog meter in my junk box, but I needed to change it from a 1 mA full-scale ammeter to a 9-16 volts voltmeter.   

I purchased locally a large red LED to substitute for the buzzer and a cast aluminum box to put it in.  Anderson power poles plus mounting blocks were obtained from QuickSilver Radio Products.   As will be described later, a few other small components were also required.

In order to change the 1 mA meter scale to read 9-16 volts, I calculated that a 16k resistor was needed in series with the meter (R=E/I = 16 volts/.001 amp = 16,000 ohms).  The resistance of the meter itself is not significant in this case.  To provide this resistance and allow calibration of the meter, a 10k ohm potentiometer was put in series with an 10k ohm fixed resistor.  I also added a 9 volt Zener diode so the scale would read 9-16 volts rather than 0-16 volts.
  
The meter, series resistor, potentiometer and Zener diode (all in series) were connected across the input of TR5 transistor and PZ buzzer (or LED in my case).  A potentiometer on the circuit board allows setting of the desired trigger voltage for the alarm.

A free scale drawing program called “Meter Basic” by Jim Tonne W4ENE (figure right) is available on the Internet.  A more sophisticated program simply called “Meter” is also available at a modest cost.  I found the former was adequate for my needs, and allowed me to change the appearance of the meter scale as shown in the figure.

It’s simple but it works.

~ John Brodie VA7XB


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And another monitor...

Keenan VE7XEN also showed off his design for the voltage monitor at the September meeting and promptly walked away with first prize. It was a very impressive professionally produced board with surface mount components.

It reports both under and over voltage and provides both a visual and audible alarm when voltage deviates from the set parameters. Other features:

•   Multiple Alarm Methods
•   Voltage to better than ±0.1V; range 5-20V
•   Parts cost $30 per unit - single supplier
•   Safe, “field serviceable” input connection
•   Small size
•   Programmable Thresholds & Alarms
•   “Mute” button
•   Temperature Readout

See a video demo at URL: https://youtu.be/2tfH_2MmHvI and Keenan’s slides at https://goo.gl/is40MR

Nice work Keenan!

Radio station WWV to celebrate 100 years

Station north of Fort Collins broadcasts the national time standard and sets radio frequency standards 

Special Event Station activated

The world’s oldest licensed radio station, which operates from a location just north of Fort Collins, will turn 100 years old on Oct. 1.

That may sound like a long time for a radio station, but WWV specializes in time.

The radio station is best known for the broadcast of the national time standard — the atomic clock — which is closely synchronized with Coordinated Universal Time, the measure by which clocks are synchronized throughout the world.

The Northern Colorado Amateur Radio Club and the WWV Amateur Radio Club will sponsor a special event amateur radio station, call sign WW0WWV (W-W-zero-W-W-V).

The station will make as many amateur radio contacts as possible over a five-day, 120-hour operating period, starting at 6 p.m. Friday and going through 6 p.m. Wednesday, Oct. 2, operating from the WWV site.

More information: https://www.reporterherald.com/2019/09/22/radio-station-wwv-to-celebrate-100-years/