I always seem to find the coolest stuff when I’m looking for something else! While researching for a future Off Grid Ham article I happened across two on line propagation calculators that can determine what HF bands are best for any time or operating condition. There are many other similar calculators, but these are especially well done and highly recommended.
The Voice of America Coverage Analysis Program (VOACAP) was developed by the VOA to predict propagation paths and frequencies for VOA broadcasts. This algorithm would be useful to hams too, if only someone would put together a civilian version and offer it on line for anyone to use.
Well, that “someone” has come forward. All you need to do is enter data for the transmitter and receiver on the main entry page. They offer numerous choices for the TX and RX QTH in a drop down window, or you can drag-and-drop points on the world map. From there it will produce a graph with a curve for each ham band and how well it will work between the two entered points. VOACAP is capable of numerous different calculations, but the one that means the most to hams is “circuit reliability”. This factor tells you how likely it is you will be able to make a contact, expressed as a percentage. The x axis (horizontal) is the UTC time. The y axis (vertical) is the percentage.
The example below is for a path between Florida, USA and eastern Africa. It tells me that on 15 meters (the pink line) I have a 77% chance of making a contact at 1900 UTC.
The VOACAP propagation calculator will also take into account the type of TX and RX antenna, TX power, and noise levels. All these variables are easily entered:
You can produce charts predicting propagation out into the future. I’m not sure how accurate the predictions are, but if the government uses them, they are probably good. This is ideal for preppers and survivalists who have concerns about not having internet access in a SHTF scenario. All you need to do is prepare a chart going out a week, a month, or however long you feel you’ll need the data, then print hard copies and save them. You’ll have to run updates periodically to keep the charts fresh.
There is a well written user guide linked from the main page. You will need it to use all the other built in features. VOACAP is complex and has a learning curve but the amount of data one can get is breathtaking. There is more in VOCAP than you’ll probably ever need. This is a very powerful tool.
Proppy HF Circuit Prediction.
In another moment of serendipity I came across the Proppy calculator. This little gem is not as complex and will not go into as much detail as VOACAP, nor does it have nearly the depth of features, but it’s super-simple to use and will produce the most common data hams want.
As with VOACAP, you can either drag and drop your desired QTHs anywhere on the world map or enter coordinates manually. Then, enter the appropriate operating parameters in the System field. From there Proppy does it a little differently than VOACAP. The x axis is UTC time and the y axis is frequency. The color coded fields on the graph indicate the likelihood (as a percentage) of contact.
In the example below, I ran a chart for a coast-to-coast transmission across the USA. It’s a little hard to see on the screenshot, but my best odds for a successful contact are between 0200 and 1200 UTC on the lower HF bands (40, 80, 160 meters):
Proppy also has a very handy feature that will generate prediction charts a month out and present them in a downloadable .pdf file. This is one aspect where Proppy is better than VOACAP. Survivalists/Preppers can simply create a new chart every thirty days and save it on a flash drive, or print them directly. Proppy also has a well written manual but the features are so intuitive you may not need it. You can even prepare a chart to up to 12 other locations at the same time, which is great if you’re organizing a net.
What you need to know.
Having real data is always better than guessing. These calculators will help you determine a communications path to any point in the world, any time of the day. And if conditions are not good enough to make contact, you’ll know that too so you won’t be wasting your time and electrical power. For preppers/survivalists, this is invaluable data for contacting distant stations on a preplanned schedule. DXers, & contesters can see how a band’s effectiveness goes up and down over time. Both of these websites are worth a bookmark.