How much do you gain from more power?

What use is an F-call? When you get an amateur radio license, you learn that different license classes have different power limits. The basic power limit in Australia, the foundation license, or f-call, has 10 Watts as the limit. The standard license has 100 Watts and the advanced license has a maximum legal limit of 400 Watts. It's natural to think that more power gives you more reach, but realistically, what does that look like, what is the difference between 10 Watts and 100 Watts? Can you really notice a difference? From my own experiments, I can confirm that it's possible to talk to the opposite side of the earth with 5 Watts, but was that a fluke, or is there more to it? What is the difference? All things being equal, that is, the same radio, the same conditions, the same antenna, the same location, etc. - the difference between 10 Watts and 100 Watts is a 10-fold increase, or, if you have 400 Watts at your finger-tips, that's 40 times more - right? Not quite. If you recall, a dBm is a decibel-milliwatt, or said differently, 0dBm is the equivalent of 1 milliwatt. If you double the power, 3dBm, you're looking at roughly 2 milliwatt. 10 Watts is the same as 40dBm. 100 Watts is the same as 50dBm. That means that between 10 Watts and 100 Watts, there is 10dB difference, that is, there is a 10dB gain if you go from 10 Watts to 100 Watts. On a HF radio, on your S-meter, an S-point is defined as 6dB. That means that the difference between a 10 Watt contact and a 100 Watt contact is less than 2 S-points. The difference between 100 Watts and 400 Watts is even smaller. 400 Watts is 56dBm. As I said, an S-point is 6dB, so, the difference between a contact made using 100 Watts and one made with 400 Watts is one S-point. An F-call using 10 Watts, is 3 S-points worse off than an Advanced call using 400 Watts, all else being equal. Of course, depending on the conditions and the deafness of the operator on the other end, that might well be the difference between making the contact or not. If you start at S-9 with 400 Watts and there's 30dB path loss because of band conditions, you end up at S-4, but if you start with 10 Watts at S-6, you end up at S-1. The path loss has a bigger impact on your readability than the amount of power you're putting out. The main take-home is that an F-call can make contacts with their 10 Watts and they're only 3 S-points behind the big guns with their fancy Advanced license. Before you start mouthing off about the 1500 Watts allowed in the United States, that's just under 62 dBm, so just one more S-point. That's not to say that there is no benefit in upgrading your license; access to bands and modes, home built transceivers and other perks, but power shouldn't be why you upgrade. One final observation. I've noticed that if you're confident on-air, other stations hear you better. That might mean that the 400 Watts that you have as an advanced licensee might make you more confident, thus making more contacts. Be brave, be confident, make your contacts with as little power as you can. I'm Onno VK6FLAB