[time-nuts] FRK-L Rubidium

[Ed Palmer]

Hi Garren,

I suggest that you get the Thunderbolt working first.  Without a known 
10 MHz source to compare to, you're flying blind.  Once the Tbolt is 
running, you should be able to check the frequency of the FRK by feeding 
both into your scope.  Trigger on the Tbolt and watch what the FRK 
does.  You should see the trace scrolling in one direction, then slow 
down, then stop, then scroll the other direction.  The 'stop' point is 
at 10 MHz.  The frequency sweeps a total of 20-30 Hz so it's easy to 
see.  If you don't see the 'stop' point, the FRK isn't getting to 10 
MHz.  Now use the best frequency counter you've got to measure the 
Tbolt.  Regardless of the calibration of your counter, the number your 
counter gives you becomes your 'new' 10 MHz.  Now measure the FRK to see 
if it's running fast or slow.

You should check the temperature of the lamp.  It's easy to get at by 
removing the cover in the center of the heat sink.  Probably best to 
remove the cover and then power down before you go poking around 
inside!  The temperature of the cavity is also important, but getting to 
it is more of a hassle - don't go there if you don't have to.

Of course, check for the normal things like internal power supply 
voltages, ripple, current drain (both initial and steady-state), etc.

Regarding your second message, yes, the adjustment under the heat sink 
near the edge is the C-field.  That won't help you at this point.  The 
adjustment in the center of one side is the VCO.  You could try 
adjusting it, but like I said, you're flying blind at this point.  You 
won't know if you're adjusting closer to 10 MHz or further away.

Good luck,

Ed


On 2/8/2013 6:12 PM, Garren Davis wrote:
> Been lurking on the list for a while and finally started playing with a FRK-L  rubidium frequency standard. I've had this thing for a while and decided to power it up and see what it would do. I do not get a lock. What I see is the lamp voltage at 8.54 volts which I think is good but the xtal control voltage swings from 2 volts to 15 volts and back to 2 volts and keeps cycling like that. I don't have a good frequency counter but I have a 3 Ghz 40 G/sample scope and it shows that the 10 MHz signal is there. I just don't know how accurate it is. Has anyone seen a problem like this? Can anyone point me to a place to start debugging this? I have the schematics and test tools. I am a test engineer so I'm not afraid to poke around in the guts of this thing. Hopefully I can get this thing running. I also have a thunderbolt that I'll get running this weekend. I don't know how deep I'll get into this time-nuts thing but I have this nice scope and a Wavecrest sitting in my garage and I'd like to put them to use. Any help would be appreciated.
>
> Garren