Another option is a Very Low Drop Out regulator like G4COL described in the latest SPRAT (issue 201) page 12. More efficient than a buck regulator, all analog, and capable of huge currents.
I built mine for a 12 volt output and when it's running off of a "12.8" volt 4S LiFePO4 battery anything above 12.0 volts coming into the regulator from the battery (including its 14.6 volt initial charge) results in a 12.0 volts available to the transceiver. When the battery discharges below 12 volts then the output is just millivolts below the input. . . essentially the same coming out as going in! All the way down to 8 volts (which is below the level where you begin ruining the battery). My adaptation uses less than 1 mA for itself.
I used what I had in my junque box: Substituted an IRF4905 (74 amp when sufficiently heat-sinked!) MOSFET, a couple of plastic 2N2222 generic switches, and an LP2950-5 LDO regulator for the reference. I also chose a 100K resistor for the gate bias for better operation at high current when below the regulator output voltage, and a higher emitter-to-ground resistor value as well as my own fixed values for the divider network. It's all very non-critical and could be built for less than $5 USD for new parts.
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73, Don
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Don, ND6T