Propagation Predictions - getting the big picture
Ask most Hams about Radio Propagation and they will tell you...
- It's influenced by the Sun and its Solar Cycle
- Impacted by the earth's geomagnetic field
- When the Solar Flux Index is high and the geomagnetic indices are low, propagation will be better
- Propagation varies with the time of day
and that's probably it.
You might also get the advice "listen around and you'll get an idea of propagation conditions".
If you are planning a serious effort in a contest, trying to work a new DXCC country or putting a plan together for a DXpedition, you really need to know how propagation varies by band through the day and how this impacts the signal you will lay down in different geographies. I call this the Big Picture of Propagation - knowing for your station (antennas and output power), solar conditions and the time of year, how strong your signal will be - where and when!
Here's an example:
Fortunately there are software engines that incorporate many years of reasearch and observations into HF propagation and its influencing factors. The "gold standard" of these is the VOACAP prediction software that was developed for the Voice of America to plan its transmitter and antenna requirements. We can use the VOACAP engine to build out the big picture.
The big picture is only useful when it is representative of your station and the stations you expect to work. This means using antenna configurations and power levels that model what you have at your station and then selecting receive antennas you would expect at the receiving station.
Producing a prediction for a single band/hour combination isn't complicated once you have mastered the learning curve of VOACAP. But doing this for all bands and all hours by hand is a LOT of work! Trust me - I used to do this manually and it took the better part of half a day even once I got the hang of it.
The desire for the big picture on a regular basis drove me to design and implement my Propagation as a Service web site - K6TU.NET. Using the service, I can produce a full set of predications in a few minutes - typically 3-4 minutes or less. I use these predictions to plan my strategy for a contest weekend or for chasing specific DX stations - the big picture helps me understand what bands I should use when I want to work specific geographies. This is really helpful in contests like the CQ WPX events where inter-contintental QSO's on 40m and below are worth 6 points!
The image above shows you a single GIF generated from each of the band/hour images you can see in an online gallery. You can scroll through them quickly in a browser window to see the same effect. I thought aggregating these all into one image was a good demonstration of the big picture.
I recently gave a presentation at the 2013 International DX Convention at Visalia, California on this topic -Propagation Predictions and DX Strategy - a PDF of the presentation is available via the link. This presentation covers the use of the VOACAP Propagation Prediction software to generate the big picture and gives some do's and dont's for the process.
I got a lot requests to put the presentation on line so figured it would make a good post.