Customizing, Using and Understanding W6ELProp

Submitted by Larry, K4WLS
Copyright 2004 Magnolia DX Association. All rights reserved.

General

W6ELProp is a very basic, easy to use, but reliable propagation program. You will, however, need to customize the Options Menu for your particular station and better understand what the propagation prediction numbers actually mean in order to make your predictions more reliable. W6EL is programmed to assume that both you and the DX station are using 100W output to a half-wave dipole at a height of one-half wavelength. If you are using yagis, which have power gain relative to a dipole, the Additive Signal Level Constants in the Options Menu require modification. Also, if the DXpedition or DX station that you are looking for is using a yagi and amplifier, the Additive Signal Level Constants in the Options Menu should be changed to reflect the power gain of these devices. Modification of the Additive Signal Level Constants for the preceding will make your predictions much more accurate and help get you that DX QSO. This article is based on W6ELProp Version 2.70. Where "W6EL" is used in this article, it is reference to W6ELProp. W6ELProp is made available as "freeware" by its author, Sheldon C. Shallon, W6EL at http://www.qsl.net/w6elprop/.

W6EL only uses the great circle path for the Short Path and Long Path in calculating its predictions. It does not take into account any skewed paths due to propagation anomalies. Also, W6EL only uses the Maximum Usable Frequency (MUF) at the two end points (Terminals A and B) in making the predictions. It does not take into account the MUF along the great circle path. This can cause some prediction errors for paths over the North and South Polar Regions since the MUFs in these regions can often be considerably less than the MUFs at the two end points.

Customizing W6EL for Your Station:

Select the Options Menu

Frequencies and Constants Tab:

Additive Signal Level Constants (db): For the frequency bands that you are using antennas (such as yagis) that have power gain relative to a dipole, enter the Power Gain in db (decibels) for the particular antenna. This will be a positive number, for example + 6 db. Only enter the number, i.e. 6, and not the sign or db using Modify Constant. You can find the Power Gain in db for your yagi in the manual that came with the antenna. Usually for multi-band yagis, the Power Gain in db will be slightly different for each band. If you cannot find the gain of your yagi, 6 db is a good ballpark figure for a three element tri-bander, and 7 to 9 db is a good ballpark figure for multi-element mono-banders, and multi-element 20 thru 10M interlaced element arrays.

For the frequency bands that you are using a vertical, dipole, inverted vee, or short inverted L, these antennas have 0 db Power Gain. If you are using a long wire or inverted L that is longer than 5 wavelengths at the operating frequency, 3 db is a good ballpark figure, since these antennas do have power gain in the direction in which they are run.

Prediction Parameters Tab:

Minimum Radiation Angle (not the Angle of Maximum Radiation): Set to 5.0 Degrees. An antenna actually has to be at a height of 3 wavelengths to achieve significant radiation at this angle; however, much lower antennas will have some radiation at this angle. Here is the reason we want to use this angle. During the periods of sunrise and sunset, there is a gradual change in the refractive index of the ionosphere from a smaller number to a larger number in the direction of the more sunlit portion of the earth. This makes the ionosphere appear to be tilted toward the earth in the direction of the darker portion of the earth. This phenomenon is often referred to as Ionospheric Tilting. Ionospheric Tilting is what allows us to gain access to the Gray-Line. Also, by using a low angle such as 5.0 Degrees, the probability of LP propagation will fall out of the woodwork of W6EL.

Noise Bandwidth: Set to 250 Hz or 500 Hz for the filter you use if you operate mostly CW. Set to 2700 Hz for a normal SSB filter or 2300 Hz for a narrow SSB filter if you mostly operate SSB. If you operate about 50/50 CW and SSB, a setting of 1100 Hz is a good compromise.

Man-Made Noise Environment: Use the setting that best fits your QTH. I live in a residential neighborhood in an older part of town, and I am surrounded by miles with some the oldest power lines in town. Since my QTH is rather noisy, I use the Industrial setting.

Signal Level Suppression Threshold: If propagation conditions are good, which usually means that K < 3, and A < 12, set to -10 db. If propagation conditions are not good, which usually means that K >=3, or A >= 12, set to -20 db.

User Preferences Tab:

Primary Solar Index: Set to Solar Flux

Primary Signal Display: Set to Signal Levels. When a propagation prediction is run, the signal levels will be in decibels (db), referenced to 0.5 uVolts (microVolts).

Time Display: Set to UTC

Make sure you "Save and Exit" on the Options Menu!!!!

What Do Those Numbers Beside the Letters Really Mean for a Prop Prediction?

The numbers, some of which are negative, that you see by the letters are the predicted signal levels in db (decibels) referenced to 0.5 uV (microVolts). The problem here is that the RX section of almost all XCVRS in use today have a sensitivity much less than 0.5 uV. The sensitivity of a receiver is defined as the amount of antenna input signal voltage that will result in a 10 db *Signal to Noise (S/N) ratio at the output (speaker or headphones). For example:

Ten-Tec Corsair (1985): .25 uV for 10 db S/N ratio
Icom IC-765 (1992): .10 uV for 10 db S/N ratio (Hard to beat this one !!)
Kenwood TS-870 (1997): .20 uV for 10 db S/N ratio
Kenwood TS-570D (2000): .15 uV for 10 db S/N ratio Back to these later !

* This is actually (Signal + Noise)/Noise Ratio now. The change was made back in the mid 70.s. From an engineering standpoint, this is a fudge factor, and I don't agree.

Depending on your display, the S Meter in your rig may appear to be linear, but it is not as it is based on a logarithmic scale. This is because it takes increasingly more signal to get one more S Unit. In order to understand what the numbers beside the letters really mean and to make them much more accurate than using 0.5 uV as a baseline, we need to do a little math. We need to use the formula to compare two voltages and get the result in db. That is:

db (Voltage Gain) = 20 log (V2/V1) This is a base 10 logarithm

The *standard for S Meter calibration is a 25 uV signal at the antenna terminal for an S9 reading. Assuming < 5 % of the Input Signal (say 3 %) is composed of Noise, and that the Noise Figure for the RCVR is < 1.5 % of the Input Signal (say 1.4 %), then, 3 % + 1.4 % = 4.4 %, and 4.4 % of 25 uV = 1.10 uV.

So, we connect a signal generator to the XCVR antenna connector, set the output of the signal generator to 25 uV at 14.1 MHz (mid-band) and set the S Meter for an S9 reading, while considering the noise content of the input signal and the Noise Figure of the RX.

Mathematically: db = 20 log (25 uV/1.10 uV) = 27.1 db

*Ten-Tec uses the IEEE standard of 50uV for S9 S Meter calibration. If you do the math and use the same proportionate amount of noise, you still get 27.1 db.

So, 9 S Units = 27.1 db of Signal Voltage (compared to noise)

And, 27.1 db/9 S Units = 3.0 db of Signal Voltage for 1 S Unit *** 1 S Unit = 3 db ***

About done with the math, but now we need to average the sensitivity of the transceivers listed in the preceding and compare this average with the W6EL reference of 0.5 uV:

(.25 uV + .10 uV + .20 uV + .15 uV)/4 = 0.175 uV (our Average XCVR Sensitivity)

Comparing this to the W6EL reference level of 0.5 uV:

db = 20 log (0.5 uV/.175 uV) = 9.1 db And, since 1 S Unit = 3 db

9.1 db/3 db = 3.0 S Units

If you got lost with the math, don't worry about it. What we have done is change the W6EL Reference Level for prop predictions from 0.5 uV to .175 uV to conform to the sensitivity of the average XCVR. In doing so, we have gained an additional 9.1 db or 3.0 S Units of received signal. To show the additional gain, let's just use 9.0 db and put both numbers in brackets to keep track of them:

*** So, we now have [9 db] = [3 S Units] of additive signal for each prediction ***

Some Sample Prop Prediction Numbers - What They Now Mean:

0 = 0 db: 0 db + [9 db] = [3 S Units]. The predicted signal strength is 3 S Units. This seems like a good place to start for a prediction period (especially if there is an "A" beside the 0). It is also a good place to stop a prediction period. If you do not see a 0 to start or stop a prediction period, use the time for the next highest positive number listed.
5 = 5 db: 5 db + [9 db] = 14 db. 14 db/3 db = 4.7 S Units predicted signal level Remember: 1 S unit = 3 db.
15 = 15 db: 15 db + [9 db] = 24 db. 24 db/3 db = 8 S Units predicted signal level.
25 = 25 db: 25 db + [9 db] = 34 db = 27 db + 7 db = S9 + 7 db predicted signal level.
-3 = -3 db: -3 db + [9 db] = 6 db = 3 db + 3 db = 2 S Units predicted signal level.

Instead of adding + [9db] = [3 S Units] to each predicted signal level to compensate for the sensitivity of the average XCVR, you can go to Additive Signal Level Constants (db) on the Frequencies and Constants Tab of the Options Menu and add 9 db to each band using Modify Constant. What was originally 0 db will now become 9 db. If you do this, you will need to start and end your prediction period using 9 db or the next highest positive number listed. 9 db = 3 S Units of received signal strength.

Customizing W6EL for a Particular DXpedition or DX Station

Once you have customized W6EL for your station, it is very easy to modify the Options Menu to include the power gain in db of antennas and amplifiers that a DXpedition or DX station will be using. The antennas and amplifiers that a DXpedition will be using are almost always published in the major DX bulletins such as the Weekly DX or QRZ DX. Including the power gain of antennas and amplifiers in the Additive Signal Level Constants (db) will greatly improve the accuracy of your predictions, provide a wider band opening window, and greatly improve your chances of working a new one. The best way to illustrate how this is done is by using an example:

Suppose you know the following about an upcoming DXpedition to Europa Island (FR/E): The team will be using a tri-band 3 element yagi for 10/15/20M, a ground plane (vertical) for the WARC bands, an inverted vee for 80M, and a sloper for 160M. They will also be running a linear amplifier on all bands capable of 700W output maximum.

You do not know the power gain in db for the yagi. Since it is a tri-band 3 element, use our ballpark figure of 6 db for the power gain of this antenna. The ground plane for the WARC bands, the 80M inverted vee, and the 160M sloper do not have any power gain. It is highly doubtful that they will running the linear at maximum output power all the time, so assume a lower output power such as 600W. Using the Power Gain (db) formula:

db (Power Gain) = 10 log (P2/P1) This is a base 10 logarithm.

Using 100W as the reference: db (Power Gain) = 10 log (600W/100W) = 7.8 db for the amplifier.

In the Options Menu, Frequencies and Constants Tab, increase the numbers in the Additive Signal Level Constants (db), using Modify Constant:

7.8 for all bands for the linear amplifier
6 for 10, 15, and 20M for the tri-band yagi

Before making these changes, it might be a good idea to make a note of the settings for your station, so that you can later restore the settings to the proper values.

Make sure you "Save and Exit" on the Options Menu

Here are some Power Gains in db for an amplifier referenced to 100W
200W Output: 3 db500W Output: 7 db800W Output: 9 db
300W Output: 4.8 db600W Output: 7.8 db900W Output: 9.5 db
400W Output: 6 db700W Output: 8.5 db

How Does My Output Power and Antenna Affect My Signal at the Receive End?

This section does not really directly relate to W6ELProp, but I think you will find the contents informative, enlightening, and probably surprising.

It can be shown, using Ohm's Law, that if the Source Power is doubled, the voltage across a resistive load will increase by a factor of 1.414. Yes, Ohm's Law applies to electromagnetic theory.

So, if we double the transmitter power, using the db (Voltage Gain) formula:

db (Voltage Gain) = 20 log 1.414 = 3.0 db = 1 S Unit of increased signal level at the receive end (under ideal conditions of course).

We can also prove the same point using the db (Power Gain) formula. Suppose you increase your XMTR output power from 100W to 200W (double output power):

db (Power Gain) = 10 log (200W/100W) = 3db = 1 S Unit of increased signal level at the receive end.

Suppose you replace your 20M dipole with a muli-element 20M Mono-Bander with a Power Gain of 12db: 12 db = 3 db + 3 db + 3db + 3 db = 1 S unit + 1 S Unit + 1 S Unit + 1 S unit = 4 S Units of increased signal level at the receive end. Hmmm.... 4 S Units doesn't seem like much for the effort and expense of putting up a tower and yagi does it. Well, you also have to consider that a yagi has front to back and side signal rejection. Also of most importance, you can point the yagi, but you can't point a dipole. Also with the dipole, your signal might be S2 in a big pile-up, but with the yagi it would be S2 + S4 = S6. This would probably make the difference in being heard or not !!

Suppose you buy a hefty linear and decide to run 600W output on CW with the 20M Mono-Band yagi described above (12 db Power Gain):

For the linear (100W as reference): db (Power Gain) = 10 log (600W/100W = 7.8 db.

12 db (for yagi) + 7.8 db (for linear) = 19.8 db. Since 1 S Unit = 3 db, 19.8 db/3 db = 6.6 S Units of increased signal level at the receive end.

If you do not want the expense and trouble of putting up a tower and yagi, a rotary dipole such as the KLM (which covers 40 thru 6 M) mounted on a 30 ft steel or thick-gauge aluminum pipe mast combined with a good linear will make a big difference in your signal. The KLM rotary dipole can be easily turned with a light-duty Ham or heavy-duty TV rotator.

Also, if you want to work some good DX on 40M, try a full size homebrew quarter-wave vertical (33 ft) with 36 radials each 33 ft long, and a linear running about 600W output.

Some Handy Tables and other Good Stuff

W6EL Reference Signal Level

Instead of using the average XCVR Sensitivity of 0.175 uV to compensate for the W6EL reference signal level of 0.5 uV, you can use the actual sensitivity of the RX in your XCVR. In the Operator's Manual for your XCVR, go to Specifications - Receiver, and find the sensitivity in uV. Use the table below and find the sensitivity that most closely matches your XCVR. Use the corresponding figure in the Additive Signal Level Constant (db) Column, and insert this figure in the Additive Signal level Constants (db), using Modify Constant, on the Frequencies and Constants Tab of the Options Menu.

SensitivityAdditive Signal Level Constant (db)
.10 uV14 db
.12 uV12.4 db
.15 uV10.5 db
.18 uV8.9 db
.20 uV8 db
.22 uV7.1 db
.25 uV6 db

No matter what Additive Signal Level Constant you use, you still start and end your predictions using a Predicted Signal Level of 9 db, or the closest higher Signal Level. Remember 9 db = 3 S Units.

Output Power and Received Signal

Here is a handy table if you are using a linear amplifier. The Power Gain (db) is referenced to 100W.

Output PowerPower Gain (db)Increase in Received Signal (ideal)
200W31 S Unit
300W4.81.6 S Units
400W62 S Units
500W72.3 S Units
600W7.82.6 S Units
700W8.52.8 S Units
800W93 S Units
900W9.53.2 S Units

Long Path Predictions

Anytime you run a prop prediction, you should always check for the possibility of Long Path (LP) propagation. In many cases, the predicted signal levels that show up will be negative numbers. This would normally mean that the signals would be below the Minimum Discernable Signal (MDS) of the RX in your XCVR if only the Normal Skywave Skip mode of propagation were considered, and W6EL only considers this mode of propagation in calculating the predicted signal levels for Long Path.

The Normal Skywave Skip mode of propagation occurs when the radio wave is refracted (or bent) by the ionosphere and returned to earth. If Multiple Hop Skip occurs, when the radio wave is returned to earth, it is reflected by the earth's surface in the direction of the ionosphere, refracted again and returned to earth, possibly for another reflection and refraction. This results in multiple hops and long distance communications. One of the biggest problems with this mode of propagation is that the earth is not a perfect reflector, and scattering of the signal occurs during the reflection process. Scattering results in losses to the signal and signal level attenuation. If the reflection of the radio wave occurs at a location on the earth where the terrain is mountainous or rugged, extreme scattering of the radio wave will occur resulting in serious degradation of the signal. This is why you see a lot of negative signal levels many times for LP predictions. The signals are there, but W6EL is saying they are very weak when considering only the Normal Skywave Skip mode for LP propagation.

When you run a W6ELProp prediction for LP, make sure that block Suppress Zero-Availability Predictions is NOT checked on the Predictions Parameter tab of the Options Menu. The will ensure that all LP signals will show up, no matter how weak W6EL Prop considers them to be. Make of the note of the times and bands for the least negative numbers (strongest signals). Many times the LP signals will be much stronger than what W6EL predicts, since W6EL does not take into account a frequent propagation phenomenon known as Chordal Hops.

Chordal Hops

LP propagation via Chordal Hops most frequently occurs during the early morning and late afternoon hours for the transmitting and receiving terminals (and vice versa). The Chordal Hop path typically follows the curvature of the Gray-Line, but the path itself is in the daylight portion of the Gray-Line. The Chordal Hop path can be anywhere from 50 to 500 KM inside the daylight portion of the Gray-Line where the Fl and F2 layers of the ionosphere are prominent.

To enter the Chordal Hop mode, a radio wave at the transmitting and receiving terminal most usually enters and exits the ionosphere during a region of Ionospheric Tilting. In this region, the F1 and F2 layers have combined to form the F layer and the D layer is not present. The radio wave may travel one or two hops in the Normal Skywave Skip mode (F layer refraction, and earth reflection), until along the path it reaches a region of high ionospheric ionization. In this region, the F layer becomes separated to form the F1 and F2 layers, and the F2 layer is at large height from the F1 layer. This is the Chordal Hop region. In the Chordal Hop region, the radio wave is refracted downward by the F2 layer and upward by the F1 layer. Depending on ionospheric conditions, the radio wave may travel distances upwards of 12,000 KM in the Chordal Hop mode being refracted downward by the F2 layer and upward by the F1 layer. This phenomena is very similar to Tropospheric Ducting of VHF radio waves.

In the Chordal Hop mode of propagation, since the radio wave is not reflected by the earth, the path loss is very small. Eventually, the radio wave reaches a region where the ionization of the ionosphere is less intense, the Fl and F2 layers combine to form the F layer, and the radio wave reverts back to the Normal Sywave Skip mode of F layer refraction and earth reflection. Since the LP signal has traveled the majority of it's journey in the Chordal Hop mode, received signals are tremendously strong, and very much stronger than what W6EL Prop would predict for the LP.

Well Known Chordal Hop LP Routes

Here are some well known Chordal Hop LP routes from the East Coast and Mid-West:

Late Afternoon, Mid-February to Mid-March - Western Australia and beyond, and Southern Malaysia: Predominately 20M.

0700-1000 Local, Early to Late Summer - Eastern and Southern Africa, and Indian Ocean: 20, 15, 17, 12, and 10M (17 through 10M depending on Solar Flux).

0800-1000 Local, Early Fall - Western Australia and S.E. Indian Ocean: 20M

0500-0700 Local, * December - Malaysia, Indonesia, and S.E. Asia: 40M

Sunset to 1 Hour Before, Fall to Mid-December - Middle and Eastern Asia: 40M

0700-0800 Local, Mid-December - Middle East: Predominately 20M

Sunset to 1 Hour Before, Mid-December - Northern Middle and Eastern Asia: 20 and 40M (20M depending on Solar Flux).

* Sporadically as late as early March

After All is Said and Done

After you have customized the Additive Signal Level Constants (db) in the Options Menu for the power gain of your antennas and the sensitivity of your receiver, when you run a prop prediction, remember:

A W6EL Signal Level of 3 = 3 db = 1 S Unit
A W6EL Signal Level of 6 = 6 db = 2 S Units
A W6EL Signal Level of 9 = 9 db = 3 S Units
A W6EL Signal Level of 27 = 27 db = 9 S Units = S9

A W6EL Signal Level of 30 = 30 db = 27 db + 3 db = S9 + 3 db

*** 3 db = 1 S Unit ***

*** Please do not add the power gain of YOUR linear to the Additive Signal Level Constants (db). The power gain of your linear will not help your received signal at all.

W6ELProp is a two-way street. Once you have modified the Additive Signal Level Constants (db) for the power gain of your yagis and to compensate for the sensitivity of your RX, the predicted signal levels not only tell you what the signals levels are predicted to be on your end, but also what they are predicted to be on the DX end !! The sensitivity of the RX section on the DX end will usually be very close to yours. Of course, if you are a running a linear amp and the DX is running 100W, your signal on the DX end will be stronger than what W6EL predicts. Also, if the DX is running more than 100W and/or an antenna with power gain, the signal levels will be stronger than what W6EL predicts.

The exact longitude/latitude of your QTH, in both decimal and minute/second formats, can be found at http://www.topozone.com


"Customizing, Using, and Understanding W6ELProp" is the property of the Magnolia DX Association. As such, it is protected by the federal statutes governing copyright material. Please feel free to take notes on this article if needed for your own personal use, however, reproduction of this article in whole or part for republication is prohibited by law except with the express consent of Floyd Gerald, N5FG or the MDXA Webmaster, John Bergman, KC5LK at webmaster@mdxa.org .
W6ELProp (W6EL Propagation Prediction) is copyrighted to Sheldon C. Shallon, W6EL, all rights reserved.


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