[PSDR] Rubidium Frequency Standard

[Bart Kus]

Hello,

I've finally become successful in my long quest to have a working 
frequency standard.  Here's the all-integrated unit I just finished 
putting together:

http://imgur.com/a/IzROb

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 
quite hot!

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!  :)

--Bart