From my understanding (which may very well be off) more ohms is better for power handling (around 75 ohms is ideal) while fewer is better for reception (around 35 ohms is ideal) and 50 Ohms was right in the middle of those two, so that's why it's used. But for QRP we're not using high power, so why not chose a lower ohm coax for better reception?

Hey, I am studying for my ham licence and am joining my local emergency preparedness group. My question is around all these portable radios like the IC-705, the EX2/3,the new TX-500 (the current one I'm leaning towards) that are around 10W. I know others like the FT-817/8 are down around 5-6W and have a huge following. I live on one of the Gulf Islands between the mainland and Vancouver Island. Line of site is not very far in most directions, though there is a peak fairly close to me that I can get to the top of within an hour's walk. I'd like a portable setup for emcomm during a long term, grid-down scenario like after an earthquake. So a low power rig is what I'm looking for for using on solar power. I may also need to walk to the local school which is designated as our Emergency Operations Centre, or up to the top of said peak, so light weight and packable is important (I'd likely be carrying a lot of food, water, clothing and camping gear as well!). I'd be relying on a combi of ground waves and NVIS. The range I'm thinking I'll need for voice communications is only 100km or so to the local major cities and surrounding islands and communities. The government will supply a large VHF radio plus FRS radio they want me to use for acting as a hub and intermediary for neighbourhood contacts (on FRS) and then on VHF to police, fire, ambulance, emergency social services, coordinating boats for bringing supplies to, or people off the island, that sort of thing. But their solution doesn't let us talk with Victoria or Vancouver or other surrounding islands or communities that are not line-of-sight. Nor even other parts of our own Island. Hence working with them to set up NVIS. Those who have done a decent amount of QRP NVIS, is 10W good enough for *reliable* SSB using NVIS for 100km or so? And to the extent it's not reliable, would 20W or 100W make a significant difference if the propagation just isn't there? Eg. Does 10W work 95% of the time and 100W would work 96% of the time? If that were the case I would stick with 10W. Or would 10W work 70% or the time, 20W would work 95% of the time, and 100W work 99% of the time? That would make me get a 20W or potentially even a 100W capable tranceiver.

NOTE that I am planning on getting very good at building excellent antennas. Also, I know CW and data modes will work fine with 10W, thats not what I'm interested in - I want to know what power output is needed for voice communication capability, as CW and data will work at that power level too.  Thanks for your input!