What Use Is An F-call?

What use is an F-call? I've spent the past couple of weeks investigating Magnetic Loop Antennas and during that process got distracted by propagation. I've talked about propagation before, but in talking with an Amateur with many years of experience, so much so, that they have had their licence longer than I've been alive, it transpired that there were still things that I was able to share that were new. The Australian Government, that is, the Bureau of Meteorology has a Department called the Radio and Space Services, which is their space weather branch. The more common name of this section is the Ionospheric Prediction Service or IPS and their website can be found at www.ips.gov.au. When you get there, you'll find a vast treasure trove of information, both historic and current, even live. Of particular interest to us as Amateurs is the section which innocuously is titled "HF Systems". Within that you'll find hourly area prediction charts, the current and past T-index with future predictions, M