[time-nuts] FRK-L Rubidium

Mon Feb 18 11:04:33 EST 2013

Bob,

Just wanted to let you know your advice to let the FRK run for a while was spot on.
The lock voltage is down to 9.2 volts.

I was able to get my thunderbolt with the bad oscillator oven working by heating the
oscillator with a power resistor. After it locked I could see on an oscilloscope that
it and the FRK were both exactly the same. I plan on putting the thunderbolt oscillator
in an oven I'm building that will have proportional control and see how that works.

Thanks for the help.
Garren

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Saturday, February 09, 2013 10:14 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] FRK-L Rubidium

Hi

Let it run for a couple of days. If it's still up at  > 11V, I'd tweak it down a bit.

Bob

On Feb 9, 2013, at 12:38 PM, Garren Davis <garren.davis at qlogic.com> wrote:

> Found my problem with the FRK. R31 on the Osc board was burned and open. This was caused by a shorted C16. Replaced and it is now locked. The lock voltage is 12.7v. Is this good or should it be lower?
>
> Garren
>
>
>
>
> On Feb 9, 2013, at 6:10 AM, "Bob Camp" <lists at rtty.us> wrote:
>
>> Hi
>>
>> How old is the FRK? Does it look like it's been run without a heat sink for very long? They tend to get flaky if run for a while (many months) without heat sinking. There's nothing mysterious about it. The MTBF of the parts gets noticeably worse as the unit heats up.
>>
>> Bob
>>
>> On Feb 9, 2013, at 1:09 AM, Garren Davis <garren.davis at qlogic.com> wrote:
>>
>>>
>>> Well for some reason the 10 Mhz stopped working on the FRK. Don't know why. Started up the thunderbolt. It acquired satellites but then the DAC voltage went to -5 volts. It's been there for an hour. Will this change after the unit stabilizes? Going to bed. Will check it tomorrow.
>>>
>>> Garren
>>>
>>>
>>>
>>>
>>> On Feb 8, 2013, at 8:25 PM, "Ed Palmer" <ed_palmer at sasktel.net> wrote:
>>>
>>>> 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

> a
>> n
>>> d
>>>> I'd lik
>>>> e to put them to use. Any help would be appreciated.
>>>>>
>>>>> Garren
>>>>
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