I run a QMX from a 13V, 30Ah LiFePo battery; my solution to the supply voltage issue is a linear regulator set for 10 V (an LM340T-5 with a resistor network to adjust the regulation point upward). I've made a 40m FT8 QSO from Boston to France with this rig and a backyard 1/4-wave dipole. Signal was logged by PSK Reporter as far as Poland. I think I'm happy with that! I'm glad to trade a little lower power output for a longer MTBF. If I really need more power, there's always the QRP Labs 50W PA.
?
For my QMX+, I plan to use a decent LDO regulator set for 10V, wired inside the unit.?
My LiFePo battery claims a nominal output of 12.8V, and I've never seen it go below that. For most of the discharge cycle, it's above 13 V.?
?
YMMV.
?
Steve N1XNX
Steve H