[NLRS] FWD: re: low cost, rubidium oscilators available

[Doug Reed]

 From the reading I've been doing, my conclusion is that the Lpro is a 
good deal although it is probably near its design end-of-life. It is a 
crap shoot how long the unit will continue to run before the Rubidium 
lamp fails. But for the price, it can still be a good deal for its 
remaining service life.

My tendency is to change the way I think about the Rb oscillator. My use 
for a GPSDO like the Z3801A is that it runs all the time and provides a 
stable 10MHz reference signal to all my test equipment. And because of 
the way a GPSDO works, it needs to be run 100% of the time. For a fixed 
location operation, the GPSDO is excellent.

But the specs for the Lpro seem to indicate it will return to "full 
accuracy" (around 10E-11) within 30 minutes of power-on. Another spec 
sheet seemed to indicate it didn't matter how long since it was last 
turned on. So if I want a portable frequency source that is only used 
occasionally but still needs 10E-11 accuracy, the Lpro can probably do 
it. And if you only turn it on half an hour before you need it, you can 
extend whatever life remains in the Rb lamp almost indefinitely.

You would probably expend a greater part of the lamp life by leaving it 
powered on long enough to adjust the Rb oscillator to match the GPSDO. I 
would think you'd want to do that at least once, just to find out 
exactly how close the 10MHz signal is anyway. On the other hand, do I 
really care if the actual 10GHz signal is +157Hz high in frequency 
compared to an absolute standard? I think all I really care is that it 
is the same +157Hz every time I turn it on, and that is what the Rb 
oscillator is best at. As they said, if your transverter is that 
accurate, you need to install a TCXO in your IF rig before you'll 
notice.....

As mentioned before, there are a lot of Rubidium Oscillators on Ebay 
right now. Just a simple search for "rubidium" in the title and body 
will find plenty of ads to read. Many are for the Lpro type oscillators, 
nearly half seem to be for the older(?) FRS unit. And a few are for 
newer units. A few are even for 19" rack mount units removed from 
cell-site service. The price for Lpro units seems to cluster around the 
same area as from SBMS, and higher. The FRS units are frequently 
cheaper, or at least no bids yet. I think one ad was for qty 4 Lpro 
units with free shipping from China for $280. Then you have the issue of 
do you trust the vendor. At least with SBMS, the element of trust is there.

But if you already have a decent 10MHz OCXO, mount it in an insulated 
box with batteries and external power, and have a 10MHz GPSDO to adjust 
it against, maybe you have an alternative to the Rb oscillator. Even if 
you don't have a GPSDO, there are probably enough people in NLRS that it 
would be possible to get your oscillator adjusted once a year or every 6 
months, just to keep your home test equipment calibrated. Face it, that 
is all most test equipment has, an internal oscillator that gets 
adjusted once a year during "calibration." We're just a little nuts 
about what we consider adequate calibration accuracy.... The 
disadvantage is that even a good OCXO has greater long-term drift than a 
Rb oscillator so the Rb would stay within "accuracy limits" longer than 
the OCXO. .

73, Doug Reed, N0NAS.

Tosca005 at umn.edu wrote:
>  5) Long-life lamp, designed for 10 year life
> 6) Fairly fast turn-on to accurate output time:
>       -- 3-4 minutes to atomic lock, accuracy +/- 5e-8
>       -- 30 minutes to "full accuracy" (not defined in spec sheet!)
>  The not so good:
>   3) How "used" are they? If they have been operated already for 10 
> years,
>       there may not be much life left in them.
>