[PSDR] Rubidium Frequency Standard
me at bartk.us
Sat Dec 29 00:32:16 PST 2012
I've finally become successful in my long quest to have a working
frequency standard. Here's the all-integrated unit I just finished
Left LED = power
Mid LED = phase lock indicator
Right LED = unused. Was supposed to be PPS blinker, but this unit
doesn't seem to output PPS :/
It puts out 10MHz @ about 10dBm. Uses about 18W when running, and gets
Since I couldn't find a decent high current 15V regulator @ Fry's, I
just used a high gain (hfe min = 500) 80W/4A NPN and a 16V zener
reference with a 20mA quiescent current. The regulated ~15.5V feeds the
secondary 5V regulator, which is a normal 7805.
The lock LED was a little tricky. The lock output from the unit is
active-low (GND), but in the unlocked state it hovers around 2.5V
output. I had to use a 22k pull-up (to +5V) resistor to eliminate glow
from the indicator LED, while not taking too much current out of that
weak pin when it's active (low). You can do fancier things with a pair
of transistors, but given this is all rats nest wiring, that's too
complicated. A single resistor works just fine!
The mounting screws may seem overkill, but they serve the purpose of
heat-sinking the rubidium unit to the aluminum chassis.
The +15V supply output during the high-current warm-up period is not
pretty. Quite the ripple is visible, but it does not seem to affect the
unit at all. Once lock kicks in the +15V bus current draw drops off
quite a bit. 60Hz harmonics are not a problem in the output, measuring
about -73dBc. It's not the best, but it's good enough for my purposes!
Using this I can now calibrate all the signal sources and spectrum
analyzers for frequency accuracy! Yaaaaay! :)
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