Some time ago (about 1 year) I acquired a Trimble Thunderbolt GPS lockable 10MHz oscillator. As I was busy at the time, making transverters for 5.7 and 10GHz and associated antennas, the Trimble was stored away, for "future reference".
During completion of my last project, a USB digital interface, I was thinking ahead about the next project. The next important item in the portable kit seemed to be a GPS locked reference oscillator.
Out with the Trimble, and I studied all the technical info that I could find, including a very good article at LeapSecond.com regarding power for the Trimble. The first thing that I noticed about the Thunderbolt, was that it had large BNC's and an 'F' connector sticking out of one side, for timing signals and the GPS antenna! My idea was to put it in as small a box as possible, and try to use it portable. I disassembled the Trimble, and found that the connectors were soldered directly to the PCB, but they weren't really needed, as the timing signals are only 10MHz. The only connector which has 'real' importance is the 'F' female for the GPS antenna, which works at roughly 1600MHz, and supplies +5V to the active antenna.
With my temperature controlled soldering iron, and a lot of care, I removed the three RF connectors, and soldered three pieces of small Teflon coax to the PCB.
I used RG-174 for the two timing signals, and RG-316 for the GPS antenna. I had a plastic box, which had housed an old 300Bd telephone modem. This seemed like a useful size, so after some measurements, I made new front and rear panels, fitted BNC connectors for signals, and an RCA connector on the rear for power.
During all of this, the thought of powering the device was always present. How could I power the Trimble from a 12V battery, without all manner of inverters for the three DC rails. With a combination of Internet sources (Ebay and Google) I came up with a workable solution. There are many sellers on Ebay, who sell "Buck" converters, both up and down from 12V. I sourced on type of downconverter, with a heatsink, for a very low price, and another without heatsink... even cheaper! For the negative supply, I used an item which very common at dump shops, field days, etc. It is the humble mobile phone charger, which contains an excellent "Buck" converter chip, the MC34063. Googling data sheets for this chip produces many project sheets, with info on up/down and +/- converters. The basic converter supply voltage can be set by a trimpot, and the current supply can be set by one resistor. So by rearranging components on this small PCB, I had my negative voltage generator/regulator.
There I had the basis for a very cheap, and simple DC supply for my Trimble Thunderbolt.
Would it all work, AND how much current would it draw from a 12V (13.8V) source.
First I removed the DC socket from the Trimble (less connections to break/come loose). I soldered an old plug on a scrap of Veroboard, and the mating socket on a lead from the Trimble, for isolation and power supply testing purposes. I tested the three power supplies, as follows...
+12V 1A
+5V 1A
-12V 100mA ... which are adequate for the purpose.
Next I connected it all together, and powered it up with an ammeter in series. WOW! It works, approximately 820mA during the heating phase, and settles to 320-340mA when idling.
The last thing, off to Ebay for a cheap 'powered' GPS antenna... replaced its MCX plug with a BNC plug, and the 'Portable GPS Locked 10MHz Reference' is complete.
Last things... the power LED has 5.6k in series with it, so it only draws about 2mA. Does the box get hot? No hotter than the original modem which was in the box!
).
Heres a shot of the STM32-SDR/UHFSDR receiving the VK5VF beacon on 144.450 MHz on the shack vertical
, and they are hand wound on a 2.5mm former...
Running it at 40V only in some faint hope that the low voltage will afford some safety margin in the event of an antenna problem. No worry about over drive, it is only driven with a FT-817ND.
A kW beacon springs to mind.. 
