Friday, June 20, 2014

Propagation Planning for IARU/WRTC 2014

If you are planning to participate in this year's IARU HF Championship contest or the WRTC 2014 contest, you might be interested to know that I have today expanded my VOACAP Propagation Planner site at

Besides running batch predictions from one TX site to all CQ Zones, it's now possible also to run batch predictions to ITU Zones (short path & long path) as well. There are one analysis tool (Win & Mac) and Excel Workbooks available to make the prediction data into more readable form.

Currently, more than 110 locations covering most of the ITU Zones are included.

The Propagation Planner gives you a good start for planning your operating strategy, especially if you run the predictions for two different sunspot numbers (SSN): 70 and 140. For low bands, use the W6ELProp software or use grayline maps for planning the best operating times.

For those who want to make predictions for WRTC 2014, use the following coordinates for the TX site: 42.29N, 71.57W.

Tuesday, June 3, 2014

New features at VOACAP Online

I have added a couple of new features (some of which are requested by users) at VOACAP Online, . The changes in the page can be seen in the screenshot below.

New sections at VOACAP Online: Propagation Params and Today's Sunrise/Sunset Times.
The Year/Month section has been moved below the Google Map.

Propagation Parameters

First, there is a new section labeled "Propagation Params", or parameters that may affect propagation. In this section you can have access to parameters which earlier were not user-adjustable.

1. Es, or setting the ionospheric sporadic E layer (Es) on and off. This may (or may not) prove useful during summer months when Es propagation conditions are quite common. Please note that the use of the Es layer is otherwise discouraged as the sporadic-E model was not fully tested during the development of VOACAP. Nevertheless, the effects of the sporadic-E layer are not totally excluded in VOACAP calculations although the layer is not set.

2. Model, or selecting the propagation model. Three choices are available here: Auto, Ducted, and Ray-hop.

  • The default "Auto" or automatic model refers to Method 30 in the VOACAP speak. It's a propagation model that chooses automatically either the ray-hop model or the ducted (forward scatter) model to predict the signal power. There is also a smoothing function for ranges of 7,000 km or greater.
  • The (forced) "Ducted" model refers to Method 21 in the VOACAP speak. Typically, this model is used for paths of 10,000 km or more. The Ducted model forces VOACAP to simulate the ducted or forward-scatter mechanisms that can prevail usually at distances having 3 or more hops. This model may produce unrealistic results at shorter distances where the ray-hops should occur.
  • The (forced) "Ray-hop" model refers to Method 22 in the VOACAP speak, typically used for all circuits less than 10,000 km. It's a model that contains multiple ionospheric reflections, and includes all of the ionospheric and earth bounce losses. This model may produce extremely pessimistic predictions at the distances beyond the third ionospheric hop where ducted/forward scatter mechanisms can occur.

3. SSN, or user-settable smoothed sunspot number. Here you can set a specific SSN (i.e. sunspot number) to be used for calculations. Note that VOACAP Online knows about the current smoothed sunspot numbers so it may be advisable not to set any value to the SSN field unless you wish to conduct propagation experiments. After you have entered a value in the SSN field, press the TAB key (instead of the ENTER key) to run a prediction.

4. Min. TOA, or setting the minimum takeoff or arrival angle for antennas at steps of 1 degree, starting from 0.1 degrees (the default), up to 5 degrees. My default value has always been 0.1 degrees due to practical reasons. However, in the VOACAP literature, a value of 3 degrees is commonly recommended, as it can be a common lowest angle for arriving skywave signals due to the roughness of the terrain. Also, 3 degrees may be a good choice if your antennas are not located in a flat, unobstructed area. And if you are using isotropic antennas, you should avoid huge amounts of antenna gain at angles below 3 degrees. You are encouraged to experiment between 0.1 and 3 degrees to see differences in predictions, using different antennas.

Sunrise and Sunset Times

The second new section is labeled as "Today's Sunrise/Sunset Times (UTC)". The label itself is pretty self-explanatory per se. In this section, the Sun's rise and set times are calculated at both the transmitter and the receiver coordinates. All times are UTC.

These calculations were originally inspired by Steve's (G0KYA) 12-year-old article about grayline propagation. In short, the best predictions for grayline propagation or trans-terminator enhancement on low bands can probably be achieved by a close examination of grayline maps. Some also swear by W6ELProp.

The abbreviation GND (for Ground) refers to sunrise and sunset at the sea level. The letter "D" refers to sunrise and sunset at the bottom of the ionospheric D region. Similarly, the letter "F" refers to sunrise and sunset in the ionospheric F region.

In the summer, if you place the TX or RX marker close to the Arctic Circle, you will see that "--:--" will appear in the D and F region fields. This simply means that sunrise and sunset times cannot be calculated for those regions (because the sun does not set/rise during the summer at high latitudes. Alternatively, in the winter, the sun may not rise/set.).