At 01:49 AM 9/1/2009, you wrote: >I have some experience with mobile HF - http://www.ke5c.net/mobile/
Me too, in the particular environment I'm talking about - rural and Outback Australia. >If you want reliable HF communications from say 50 to 500 miles, you >will need a frequency agile gateway because you are going to have to >use 160 to 20 meters depending on the time of day, and some days you >will not have a path on any HF band depending on your range. You >will also need a KW in your car as well, particularly if you need to >pay the 10 db s/n digital penalty. Typically, 80 and 40 metres are going to be the workhorses for this sort of operation. In practice, we would have to make do with these two bands for legal reasons (quirk of our regulations). As for the other bands - 160, not enough people here have mobile setups that are efficient to get much out of this band. 30m (yes we can use SSB or any other mode there) works very well at 400+ miles in the higher sunspot years. As for power, 100W has proven to be more than adequate, and QRP portable/mobile stations have managed to reach me from interstate on SSB while I was mobile (OK, rough copy, but quite useable), so the paths had somewhat more than 10dB S/N. The 25dB for digital HF applies only to the G4CUO mode. Other HF digital modes will have different S/N requirements, some more, some less. FDMDV seems to be the best performer at lower signal levels (hardly surprising, its bitrate is much less than G4CUO or DRM). My point. Don't write off digital HFvoice. It's still early days. I doubt D-STAR is going to have great performance on HF, but hey, if one can experiment, why not? Worst that can happen is it won't work. ;) 73 de VK3JED / VK3IRL http://vkradio.com