Friday, November 18, 2016

VOACAP Greyline User Manual

VOACAP Greyline is an online service that provides a number of sun-related data for any given location such as sunrise/sunset times, dawn, dusk, solar midnight, and, for circuits, the solar midnight time for the circuit's half-way point. The idea is to offer data which would help DXers/contesters leverage any "grayline" related low-band openings.

The URL:

What's in it for you?

The greyline service offers three types of solar calculations:

  1. Daily sunrise and sunset times for a wide selection of DXCC locations
  2. All-year sun calendar: sunrise and sunset times for a user-defined location for every day of the year selected
  3. A deep analysis of DXCC countries that are located along the grayline terminator or in darkness at sunrise and sunset in a user-defined location

1. Daily sunrise and sunset times for a wide selection of DXCC locations

This is the default calculation when you go to the site at The DXCC locations are the pre-defined locations used in VOACAP Online. In reality, VOACAP Greyline offers much more than simple sunrise or sunset times. Let's look into the times calculated; all times in all calculations are UTC.


There are actually seven different times which will be calculated: three related to sunrise, three related to sunset, and one related to solar midnight.

Sunrise-related times:

DAWN = a point in time when the sun is 6 degrees below the horizon before sunrise
RISE = the sunrise time at the horizon
POST = a point in time when the sun is 3 degrees above the horizon after sunrise

Sunset-related times:

PRE  = a point in time when the sun is degrees above the horizon before sunset
SET  = the sunset time at the horizon
DUSK = a point in time when the sun is 6 degrees below the horizon after sunset

Solar midnight

MNITE = This is the time opposite to solar noon when the sun is closest to the nadir (the direction pointing directly below a particular location), and the night is equidistant from dusk and dawn. The solar midnight rarely coincides with midnight on a clock. Solar midnight is dependent on longitude and time of the year rather than on a time zone. [Wikipedia:]

POST and PRE times

The POST and PRE times are based on an educated choice; there is no conscious theory behind "the 3 degrees above the horizon". We know from experience that the low-band propagation starts to deteriorate at some point after sunrise, and that the propagation starts to get enhanced before the actual sunset, and "3 degrees" was my personal choice for this purpose. So, in effect, I am using the time periods from DAWN to POST, and from PRE to DUSK as my internal limits in my calculations when filtering the results in the deep analysis (the calculation type 3).

The default date for daily calculations in the currect UTC day. If you wish to calculate times for all DXCC sites for a specific date, just select the date from the calendar, and press "Go".

To make this calculation again for the current date after setting the date (or after setting a location), just press first "Reset" and then "Go".

There can be cases where no time is calculated but "--:--" is shown instead. This means that the sun does not reach the degree position set for the calculation.

For example, let's take some Finland locations at midsummer (June 21):

CITY                          DAWN   RISE   POST   |  PRE    SET    DUSK   |  MNITE
OH6 Seinajoki                 --:--  00:25  01:26  |  19:34  20:35  --:--  |  22:30
OH6 Vaasa                     --:--  00:23  01:28  |  19:43  20:47  --:--  |  22:35
OH7 Joensuu                   --:--  00:00  01:01  |  19:04  20:05  --:--  |  22:02
OH7 Kuopio                    --:--  00:03  01:06  |  19:15  20:18  --:--  |  22:11
OH8 Kajaani                   --:--  23:34  00:50  |  19:31  20:47  --:--  |  22:10
OH8 Oulu                      --:--  23:19  00:49  |  19:50  21:20  --:--  |  22:19

As the times for DAWN and DUSK are labelled as "--:--", it means that the sun does not reach 6 degrees before sunrise nor does it go below 6 degrees after sunset. On the other hand, for instance, if all columns are labelled as "--:--", it can mean that it's either midnight sun (polar day) or polar night.

2. All-year sun calendar: sunrise and sunset times for a user-defined location for every day of the year selected

If you wish to run the solar data above for every day of the chosen year for your own location, just enter your Maidenhead grid locator in the "Locator" field, choose any date (click on a date) in the year you are interested in, and checkmark the "Calendar" option. Then press "Go".

The locator needs to be given in six characters. If you do not know your locator, please click on the "Locator" link to go to which shows you the coordinates and the corresponding grod locator with the precision required (6 characters).

Suppose we want a all-year sun calendar for Valletta (9H) for the year 2017. Then I would first check the grid locator (JM75gv) and select any date from the calendar in 2017. Then I would checkmark the "Calendar" box, and press "Go".

The result will be as follows:


3. A deep analysis of DXCC countries that are located along the grayline terminator or in darkness at sunrise and sunset in a user-defined location

This calculation type is the most elaborate. First of all, it requires that you set a location (as a 6-character Maidenhead grid locator), and set a date you are interested in. Do not checkmark the "Calendar" box! Then press "Go".

Two calculations will be done for all circuits from the location you set to the pre-defined locations in VOACAP Greyline's DXCC country list: sunrise and sunset calculations.

New columns

There will be a number of new columns on the result page as we are now dealing with point-to-point circuits. The columns are:

  • HALFW = This is the solar midnight at the half-way point along the circuit in question. This is the time ON4UN says can be one of the peak times along that circuit.
  • KM/SP and DEG = This is the distance from the Location to the DXCC location in kilometers via short-path (SP). DEG is the corresponding bearing from Locator to the DXCC location.
  • KM/LP and DEG = This is the distance from the Location to the DXCC location in kilometers via long-path (SP). DEG is the corresponding bearing from Locator to the DXCC location. If you want the distance in miles, divide kilometers by 1.609 ...

As said, the service calculates the sunrise and sunset times for the given Locator. Then it tries first to find the locations in DXCC countries that are along the grayline terminator. In those locations, the sun can either be rising or setting. The time frame for the terminator is determined by DAWN-POST and PRE-DUSK times. If the sun is rising, you will only see the sunrise-related times for that particular DXCC location, and consequently, if the sun is setting in that particular DXCC location, you will only see the sunset-related times.

Secondly, the service finds all locations in the DXCC country list where the location is in darkness. So, this is the situation when the sun rises or sets in the Location but it's still dark in the DXCC location. Think about the morning propagation of signals from the west when the sun start to rise in your location.

An example

Let me illustrate what's happening. In the image below, this is an excerpt of the result page for my locator KP03sd on November 15, 2016.


In Bullet 1, we can see that at my sunrise, the sun is rising also in 1A SMOM and in 3A Monaco. Bullet 2 reveals, on the other hand, that - at the same time - the sun is setting in 3D2/C Conway Reef and 3D2/R Rotuma. Note that in these two cases, only the sunrise or sunset times are shown, so that the user can more easily distinguish whether there is a sunset or sunrise in the DXCC location.

And finally, Bullet 3 shows that there are locations which are in darkness at my sunrise. When a DXCC location is in darkness, both the sunrise and sunset times are given for the location. The darkness period is calculated to be the time period from PRE to POST in that particular DXCC location. This actually means that the darkness period also includes the twilight period.

For instance, 8P Barbados is in "darkness" from 21:11 UTC (PRE) to 10:14 UTC (POST). And we can see that the twilight period for KP03sd is from 05:58 UTC (DAWN) to 07:47 UTC (POST). So, 8P is filtered to be part of the results as it's in darkness when the sun is rising in the given Location.

A similar kind of analysis is made for the sunset at Locator, too.


  1. I am sometimes asked for LF skeds and would like to be able to figure out the best time of year, when we have mutual greyline or darkness. For that, I'm looking for the computer to calculate (1) my greyline times throughout the year; (2) the DX stations greyline times throughout the year; and (3) the dates when both ends are in greyline or darkness. Please! 73, Gary ZL2iFB

  2. Hi Gary, my thoughts, too. The cases (1) and (2) are already available in the service, but (3) is where the real beef is. Let me see if there's an easy way to implement this...

  3. That would be fantastic. I am surprised nobody seems to be doing this already - at least I haven't found such a service despite occasionally searching over several years now! Actually I did find one but it was too complicated: they graphed out the greylines throughout the year, then superimposed both graphs ... which made it too hard to make out what was happening. Good luck!

  4. PS Happy Pi day (3.14 ...). Seems appropriate!

  5. Just to inform you that I have added "All-year solar analysis" option (button) on my VOACAP Online Point-to-Point service at It will provide comprehensive Sun-related info for the TX and RX sites, and hopefully presents them in a way which is easy to understand.

    1. Quick update: I changed the name of the button "All-year solar analysis" to "All-year grayline", just to make it shorter and perhaps more interesting :D

  6. That's useful ... and it would be even better if the periods of mutual darkness or greyline were emphasized e.g. in bold, to take the eye directly to the relevant part/s of the year when skeds might be worth arranging. :-)

  7. Hi Gary, and tnx for comments! Yes, I will think about a way to highlight the prospective times in the listings -- just need to do some "creative experimenting" :)

  8. Hi all, FINALLY: the "All-year grayline" on the VOACAP P2P site ( offers now the functionality requested: the green, red and blue colors show the periods when the grayline (understood in a broad sense) can be most favorable between the TX and RX. The more details docs will follow.

  9. Hi Jari. Many thanks for working on this.

    I wonder if it would be less confusing and easier to use with 52 weekly numbers instead of 365 daily? And/or possibly a graphical view showing how the greylines at both ends shift and intersect during the year?

    I know, I know, I'm asking a lot! To be clear, I'm very grateful for the work you have already done, in the true amateur spirit.

    73 Gary ZL2iFB

  10. Here's a typical use case that may help explain what I am looking for: 4J1XX emails me one day saying "Hi Gary. I *really need* ZL on 80m. Please can we set up a sked?". "OK", I say ... but then how do I figure out when we are most likely to make a QSO? I probably need to choose either dawn or dusk during the few days or weeks of the year that the greyline path is most likely to open between ZL and 4J.

    Using the new VOACAP report, I guess we should pick dates towards the middle of the next red or blue period for our sked?

    73 Gary ZL2iFB

    1. I think there are a plenty of options here. Running the grayline analysis between 4J (TX) to ZL2 (RX), I would first look for time periods where one end is in darkness, the other end is in sunset/sunrise, and the midpoint of the path is in midnight. So, I would first look that these three parameters are in place.

      In the grayline analysis, these periods can be found by looking for blue and red colors in the MIDPT MNITE column. These time periods happen in January, November, December (blue) & May, June, July (red). If you set the grayline dates and times accordingly (on, you will see how it will look like.

      This was the first look. The other options include looking for green time periods which mean that sunrise/sunset happens while the other end is in darkness. Red/blue in the DAWN-POST or in the PRE-DUSK columns indicate that these are time periods common for TX and RX.

    2. Hi, I added an option to view the grayline on a Google Map when you click on the date on the result page. Just click on a time button on the top row of the page. A pop-up over the time button will explain the time in question...

  11. It seems my last question did not make it onto this discussion. I will try again. I am writing software in C# using VOACAP as the prediction engine. As an extra, I would like to add a grayline map similar to the one in the Online VOACAP app. I have no idea, however, of how to implement this at all.

    So, the question is: can you release the algorithm which calculates and displays the gray line on a map, or is it sensitive and/or proprietary?

    Thanks very much.


    1. Hi Peter, it's all JavaScript. See

  12. Thanks very much, appreciate the help.