VK2FABS wrote:...
But still the question. What's the furthest contact people have achieved with 10W? How much further could 100W reach under the same condition?
A more relevant question might be not can you, but how often do you make 15,000km contacts with 10W SSB or CW (your permitted modes).
If the chance on average was one contact per thousand hours of trying, you might not find that an interesting prospect, though some will chase the rare contacts purely because they are rare.
For example, 40 years ago I worked a ZL station from Sydney simplex 2m with a 2W TR2400 FM handheld, standing on natural ground and using the rubber duckie antenna. That is an extremely unusual contact, but in answer to your question, it proves that ZL can be worked on such a setup. You could spend your life on your balcony calling on you 2m hand held and never make a contact of that distance and die an unsatisfied man.
It depends what your interest is / becomes, whether your are a train-spotter, whether you want to have a discussion with someone about something technical (though there isn't much of that these days), be driven by someone else's targets (eg awards and contests), 'login' to a net and tell them what you will have for dinner. Ham radio is a lot of different things to different people and there is room for all of it... doesn't mean you have to engage in all of it though.
Lots of stations running low power will tell you how adequate it is. I can tell you that it is a struggle most times working 40m stations running much lower power. I find that when I reduce power to 10W, most Foundation stations copy me worse than I copy them... and there are likely explanations.
It is a competetive environment when you respond to a CQ (Foundation calls rarely call CQ in my experience), stronger / clearer stations have a better chance of securing a contact. When most stations on 40 or 80m run 100W, with just 10W you are challenged and if you go chuck away a further 9W with an inefficient antenna system (easy to do), you are 20dB (or 3+ S points) behind an efficient 100W station, your are futher challenged. It is not that you cannot or will not make contacts, they are just fewer and further between. However, the other side of that coin is that you might be very satisfied with what you can do with a 1m diameter small transmitting loop and 10W on 40m.
You will not know until you try it, but see that once in a lifetime contacts might not sustain the hobby for most people.
Owen
PS: I have spent far more hours transmitting at less than 10W in the last year than at 400W... I am not QRO biased, nor anti QRP.