Battery Source

I can confirm that my Walter Dittel FSG71M functions flawlessly on
input voltages between 9 V and 14 V when powered from a variable
voltage bench supply. RF output looked pretty constant, except it
dropped a little when supply was under 10 V.

The first instrument to complain about low voltage was my SN-10 and
then my Volkslogger - they get unhappy under 10 V.

My four-year old nominally 12 V battery starts out at around 12.5 V at
the beginning of a flight and ends up at 11.8 or so after 5 hours. Bus
voltage drops about 0.4 V on radio transmit.

Current demand from my instruments, including radio on receive, is 0.28
A at 14 V and 0.39 amps at 10V and a pretty constant 0.31 amps on
battery. A five-hour flight consumes about 2 Ah, about a third of
the capacity of a fresh battery.

I have no need for a 14 V supply with my instruments.

Mike

Actually, it is an FAA requirement too. The VHF radio TSO-C37
references RTCA DO-160, DO-178A and DO-186. Part of the data submission
requirements by the manufacturer to the FAA include (this is from the
TSO):

"(viii) The results of the environmental qualification tests conducted
in accordance with RTCA/DO-160C."

Tom