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


-----------------------------------------------------------------

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/

Gel Cel Battery Charger 12 Volt—7.3 Amp

A Communicator Reprise...

September 2015

Two of my hobbies are hiking and camping.  Usually I take my QRP gear with me, including a low capacity 12V gel cell battery, which must be properly maintained or its life is short.  Some time ago, I bought two gel cell batteries at the same time. I used one of them frequently, and put the other one aside as a backup. When the time came that I wanted to use the backup battery, I found it was no longer useful as the battery voltage had dropped to a few volts and couldn't be charged.   A brand new battery went dead simply from disuse.

There is a simple and effective way to maintain the gel cell battery properly, and that is by charging the battery under a constant voltage. If a fresh battery is not being charged from time to time, it will eventually die due to the internal leakage. I use the constant voltage charger that is shown in Fig.1 to maintain my gel cell batteries.

The operating principle of this charger is quite simple. The heart of the charger is a 3-terminal LM317 adjustable regulator. The output voltage is set at 13.5V for a gel cell, but other batteries may require a slightly different voltage.

Diodes D1, D2, D3 and D4 form a full-wave bridge rectifier. The rectified current is smoothed by capacitor C1 and applied to the input of LM317. The output voltage of the LM317 is set by the resistor R1 and potentiometer Pot1. There is an internal voltage 1.25V between the output and adjust terminals of the regulator. As shown in the circuit, R1 is placed in between these terminals. Therefore, the current flow through R1 is 1.25 volts/270 ohms = 0.00463 amp or 4.63 mA. This current also flows through Pot1 and establishes a voltage drop across it. What voltage drop is needed?  As mentioned above, the output voltage of the charger is set at 13.5 V, and we get this output voltage after diode D5.   Since D5 has a voltage drop of 0.6 V in the forward direction, the output voltage of the regulator must be 13.5V + 0.6V = 14.1V. Hence the voltage drop across Pot1 should be 14.1V – 1.25V = 12.85V. Because there is 4.63mA on Pot1, the resistance of the pot should be 12.85V/4.63mA = 2775 ohms. Since there is no standard value resistor of 2775 ohms, instead a 5K potentiometer is used.

Transistor Q1, resistors R2 and R3 form a current limiter. To complete the circuit, the charging current must go through  R2 and R3. When this happen, a voltage is developed between the emitter and base of Q1. If this voltage is higher than 0.6V, Q1 turns on and it's collector draws down the voltage across Pot1.  Hence the output voltage of the charger is reduced and so is the charging current. What should the charging current be to charge a low capacity 12V gel battery? As the rule of thumb, the charging current is one twentieth of the capacity of  that battery. For example, if you have a 12V, 7.3A gel cell battery, 1/20 of 7.3A is 365mA. When 365mA goes through R2 and R3, it establishes 0.73V to the base of Q1. This voltage turns on Q1, therefore the charging current is always limited to 365mA.

Measurement of the voltage between the test points T1 and T2 will tell you the charging current. If the reading is 0.27 V, the charging current is 270 mA; if 76 mV, the current is 76 mA, and so on; 1mV corresponds 1mA.

In the circuit, D5 serves two purposes: first, it prevents damage to the charger and the battery if the output polarity is incorrect; second, it prevents the battery discharging itself through the charger while there is low or no power to the charger.

Under normal operation, there is a 3V voltage drop between the input and output terminals of the LM317, as we have calculated, the output voltage of the LM317 is 14.1V, therefore, the input voltage to the LM317 should be  14.1V + 3V =  17.1V or higher.

If you use DC only to power the charger, you can omit D1, D2, D3, D4 and C1 to simplify the circuit. You can simplify the circuit even more by removing Q1, R2, and R3 if you don't need the current limiter.  Fig.2 shows the much simplified circuit.

When a solar panel is used to power the charger, apply the output of the panel directly to the input of the LM317 rather than through the bridge rectifier, because the bridge rectifier will cause a 1.2V drop.  Even a loss of 1.2V represents a significant power loss under a cloudy sky.

Since the bridge rectifier takes away 1.2V from the power source, then why use it? Well, the reason is that with it, either an AC or DC power source can be used. When only DC power is used, it helps to prevent incorrect polarity hook up. With the rectifier being used, the input voltage of the charger should be 17.1V + 1.2V = 18.3V or higher. 18V is acceptable.

After the charger is built, a simple adjustment is needed. Adjust Pot1 to the mid-range before power is applied to the charger, then use a voltmeter to monitor the output voltage. Adjust Pot1 until the voltmeter reads 13.5V. This is it, all done. Since this charger provides a low charging current, a heat-sink is not needed for the regulator LM317, but no harm in using one.  Fig.3 and Fig.4 show the construction and physical size of this charger.

Because this is a constant voltage charger, there is no over-voltage to the battery to harm it. Also, because the charging current is limited to 365 mA, not much heat will be generated inside the battery. The charger can be connected to the battery for a long period of time and will keep the battery fully charged all the time even there is internal leakage of the battery itself. This charger may be suitable if you want to have emergency power handy to operate your QRP rigs. All the parts used to build this charger are from my junk box. Happy home brewing!

~ Hiu VE7YXG