[time-nuts] Request for infos for a quick start available time and frequency reference

Mon Feb 4 00:28:47 UTC 2019

Hi

There are a number of GPSDO’s on the market. For less than the price of a working 5071, you 
can probably buy a couple dozen of them. In terms of long term accuracy, a GPSDO will beat
a Cs. Most of them (but not all of them) will do as well as a “standard tube” based Cs at short(er)
tau’s. Compared to a system locked to an LF signal, a modern GPSDO is *way* better. 

Downsides include the need to mount an antenna with a good sky view. Keeping them on power 
all the time may or may not be a downside. 

You can indeed build one up and do it that way. When a “pre built / tested / working” device is as 
cheap as they are, there is not a big need to do that. 

Bob

> On Feb 3, 2019, at 7:04 PM, Christoph Kopetzky <ck at cksd.de> wrote:
> 
> Hi Bob and time-nuts,
> 
> thank you for your infos. It seems not to be an easy job to get a used cesium clock in a good shape
> with some reserve for a good few years of lamp live and an adaquate price.
> The ones on the market are either for parts or like the both examples at ...bay fakes which costs
> a lot of money and the not so experienced users are getting into a bigger lot of problems...
> 
> The other crux with this clocks is oviously that they need to let them running all the time for reaching
> the better stability and exactness what the should have as as a reference in the lab.
> 
> Bob your pricing info for an exchange of the cesium tube seems to be not the right direction for the hobby
> electronics user like me. I think it is a good idea not to buy such a clock at the moment.
> 
> But the problem of mine and my be a lot of electronic developer and scientists is that they cannot have their
> reference systems running all the time. It must be possible to build a reference which does not need weeks
> to reach its best exactness and stability within hours...
> 
> Is there a known solution available which allows good short time stability and also exactness which will be reached
> within a maximum of one hour after power on?
> 
> My thoughts are going into the world of the well known GPSDOs with a good OCXO inside and a precise Timing GPS receiver
> module like UBlox NEO-M8P or a Furuno GT-87xx, a high precision roof antenna with a good view of the sky, and one of
> the best rubidium oscillators such a SRS PRS10...
> This combination must do the trick. It should be not to hard to feed the pps signal from the GPS receiver into the PRS10.
> I read that the developer from SRS implemented the regulation software loop for that into the firmware of the Rubidium
> oscillator. With saving the states of the gps and the rubidium in two separate real time clocks (battery buffered) and a
> few lines of software for the microcontroller to arrange all with a display must be enough.
> 
> I would be lucky if you guys could give me some tips about that or alternatives to get such a stable reference with a short
> avalability timeframe for locking and stabilisating.
> 
> Are there may be ready useable open hardware sources available?
> 
> Thank you guys in advance for all your help...
> 
> --
> with best Regards
> 
> Chris
> 
> Am 03.02.2019 um 23:34 schrieb Bob kb8tq:
>> Hi
>> 
>> The gotcha with a Cs is the tubes wear out. Last time I put a tube in a 5071 it cost just
>> about $40,000 including custom shipping of the “hazardous” Cs. From the description
>> on that uint it does not *appear* that things are working correctly.
>> 
>> Even if you do get a working Cs standard, the question is - how much longer will the
>> tube last? It might be good for another 10 years. It might die tomorrow. That tends to be
>> a bit of a concern as far as running them all the time in a basement lab.
>> 
>> With the high performance tubes in the 5071, my experience was that 6 to 7 years of
>> continuous use was about it. The “standard” tubes in the 5071 should be good for > 2X that
>> time period.
>> 
>> None of this is to say that the *only* reason one fails is the tube. It is not at all uncommon
>> to have other stuff fail. Usually the small stuff gets fixed and they go back into service.
>> When the tubes go (or the problem is complicated) the go on the market…..
>> 
>> Indeed none of this is to say you *can’t* get a working Cs. You most certainly can. This
>> list is one pretty good place to find a working one from somebody who *knows* that it is
>> running properly. I’m not selling any of mine, but you may see emails from people who are.
>> 
>> Of course it there *was* a really good deal on a 5071 … hmmm …. maybe I need another Cs …. :)
>> 
>> Bob
>> 
>>> On Feb 3, 2019, at 5:16 PM, Christoph Kopetzky <ck at cksd.de> wrote:
>>> 
>>> Hi Bob,
>>> thank you.
>>> Wow I did not realize that. Very interesting :)
>>> B.t.w. there is a HP 5071A on ...bay item nr 263497171568. Is this cesium clock ok for buying?
>>> 
>>> --
>>> with best Regards
>>> 
>>> Chris
>>> 
>>> Am 03.02.2019 um 21:29 schrieb Bob kb8tq:
>>>> Hi
>>>> 
>>>> The key is the top view of the 5065a. You can see through the holes in the top of the unit.
>>>> There’s a big empty space to the right in the picture where the optical unit / physics package
>>>> should be. There also are a few other tidbits missing but the physics package is the biggie.
>>>> 
>>>> Bob
>>>> 
>>>>> On Feb 3, 2019, at 2:30 PM, Christoph Kopetzky <ck at cksd.de> wrote:
>>>>> 
>>>>> Hello Corby,
>>>>> in the case that this is a stupid question... I am sorry but can you tell me how I can see that the optical unit is missing?
>>>>> There are no pics of an open 5061A device...
>>>>> I am also wondering why this seller is shipping these units for this extraordinary price.
>>>>> He is telling in the description that the shipping costs will be calculated at the real destination but I will bet that the click
>>>>> on the buy it now button bounds you to pay the whole sum ...
>>>>> -- 
>>>>> 
>>>>> with best Regards
>>>>> 
>>>>> Chris
>>>>> 
>>>>> Am 03.02.2019 um 18:21 schrieb cdelect at juno.com:
>>>>>> Hi,
>>>>>> 
>>>>>> Wanted to warn about the 5065A that has now sold twice on eBay. (Jan 18
>>>>>> and Feb 2) When it first listed I contacted the seller and told him the
>>>>>> optical unit was missing (A12) and he should not call it "fully
>>>>>> functional" Anyway he sold it for his asking price and now it looks like
>>>>>> he just sold it again. If he has it returned and lists it again just be
>>>>>> aware its not all there! Not really worth the price with no A12!
>>>>>> 
>>>>>> Cheers,
>>>>>> 
>>>>>> Corby
>>>>>> 
>>>>>> 
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> 