[time-nuts] New (refurbished) LPRO-101 GPSDO

David McClain dbm at refined-audiometrics.com
Sun Oct 17 16:32:00 UTC 2010


Hi Bob,

Well,... sort of... I live in a rather cramped housing development,  
where the neighbors wall is about 20 feet from my window, and his  
wall is about 12 feet high. So that seems rather marginal for a  
southern view from the windowpane of my lab.

As it happens, I moved the antenna about 4 feet lower, to a slightly  
more restricted view of the sky, and the LPRO pretty quickly locked  
to its best state. Then after fiddling some more with the antenna it  
must have lost the birds, but still remained in its second-best  
state. Now after more fiddling, the sats were reacquired and the LPRO  
is back to its best locked state. What a huge difference this makes.

Incidentally, the antenna was originally located about 1 foot from a  
Comcast coax line running around the house, just below the eaves. I  
have had no end of frustration with Comcast equipment, and so I  
wonder if that was the culprit. Right now the antenna is sitting  
slightly higher for a better view of the south, but careful to keep  
at least 3-4 feet from the Comcast coax line. Everything is working  
great at the moment.

Very happy camper. Thanks so much for all your input. I'll give the  
groundplane idea a try with one of my wife's cookie sheets...

Cheers,

Dr. David McClain
Chief Technical Officer
Refined Audiometrics Laboratory
4391 N. Camino Ferreo
Tucson, AZ  85750

email: dbm at refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com



On Oct 17, 2010, at 08:09, Bob Camp wrote:

> Hi
>
> The antenna should do fine just sitting on the roof. It will do  
> better sitting over a ground plane.
>
> Does the antenna have a clear view of the sky to the south?
>
> Bob
>
>
> On Oct 17, 2010, at 10:15 AM, David McClain wrote:
>
>> Well, not exactly an urban jungle here, but there could be  
>> multipath off the neighbor's home... Thanks for that suggestion. I  
>> will try moving the antenna about.
>>
>> When I first deployed it, the GPS would go solid reception for a  
>> while, and it actually claimed to lock, after only an hour or so.  
>> But it kept losing the birds and would go back into hunt mode  
>> after about 20 minutes of lock time. I wasn't sure that I could  
>> trust the lock indication after so short a time. And I didn't like  
>> the sporadic lock conditions.
>>
>> So I tried duct taping the antenna to the roof tiles that I could  
>> reach and got solid GPS reception, but no lock.
>>
>> The antenna is a little black hockey puck with a magnetic base. I  
>> wonder if it would do better affixed to a metal ground plane?
>>
>> First time user of a GPSDO and so I don't know what to expect. But  
>> I'm also beginning to understand better that a GSPDO probably is  
>> more than was warranted for the needs of a solid reference  
>> oscillator for radios. Now that I'm learning more about Rb and  
>> GPSDO's in general, I probably could have got by quite well with  
>> just a bare LPRO. And I am also beginning to understand that  
>> GPSDO's don't necessarily have internal Rb references -- looks  
>> like the T'Bird is just a really good OCXO with a GPS discipline.  
>> And everyone is raving about T'Birds... The LPRO has an internal  
>> Rb reference and an untamed VCXO.
>>
>> Thanks for all the advice!
>>
>> Dr. David McClain
>> Chief Technical Officer
>> Refined Audiometrics Laboratory
>> 4391 N. Camino Ferreo
>> Tucson, AZ  85750
>>
>> email: dbm at refined-audiometrics.com
>> phone: 1.520.390.3995
>> web: http://refined-audiometrics.com
>>
>>
>>
>> On Oct 17, 2010, at 06:07, mike cook wrote:
>>
>>>
>>>
>>> Le 17/10/2010 11:55, David McClain a écrit :
>>>>
>>>> I just received my LPRO-101 with a GPSDO control on it, from  
>>>> TenMhz.com. After fiddling with getting a good placement for the  
>>>> GPS antenna, so that it doesn't keep losing the satellites, I  
>>>> have been attempting to discipline the oscillator for more than  
>>>> 24 hours.
>>>>
>>>> At this point, the LED has been toggling red / green for the  
>>>> past 24 hours which indicates solid GPS acquisition and < 5e-8.  
>>>> But it isn't locked to NIST until it turns solid green which  
>>>> indicates < 5e-11.
>>>>
>>>> Since this is a first deployment at my location, is it  
>>>> reasonable behavior for it to take longer than 24 hours to lock  
>>>> to NIST through GPS? Or do you think something may be wrong with  
>>>> the device.
>>>>
>>> I don't have this box or an LPRO, but if the manafacturer says  
>>> 24hrs is OK, then I guess that should be enough.  You may need to  
>>> give them a call. However am wondering if you are getting  
>>> reflected path GPS signals. You said  that you had to fiddle with  
>>> the antenna placement. Are you in an urban jungle? I have a  
>>> situation where I can see satellites at all times, but once or  
>>> twice a day I am getting strong reflected signal which is  
>>> disturbing the GPS 1PPS. It is due to buidings opposite my north  
>>> facing office where the antenna sits. The issue is seen with my  
>>> TBOLT, Z3801A and  independent Oncore GPS engines all of which  
>>> are not the latest hardware.  That would cause the PLL to be  
>>> constantly chasing a moving target.
>>>> I already know by comparison to WWV that I'm within a few mHz of  
>>>> being aligned, but noise in the measurements, human impatience,  
>>>> and wander in the soundcard clock, prevents me knowing any  
>>>> better than this. So already I'm < 5e-10. But that's about all I  
>>>> know until I see it lock. (If it ever does...)
>>>>
>>>> eh?
>>>>
>>>> Dr. David McClain
>>>> Chief Technical Officer
>>>> Refined Audiometrics Laboratory
>>>> 4391 N. Camino Ferreo
>>>> Tucson, AZ  85750
>>>>
>>>> email: dbm at refined-audiometrics.com
>>>> phone: 1.520.390.3995
>>>> web: http://refined-audiometrics.com
>>>>
>>>>
>>>>
>>>> On Oct 15, 2010, at 16:00, Magnus Danielson wrote:
>>>>
>>>>> On 10/16/2010 12:08 AM, Bob Camp wrote:
>>>>>> Hi
>>>>>>
>>>>>> It's a crazy world when it comes to self signed certs.
>>>>>>
>>>>>> You have at least 5 OS's you need to consider (MS, Linux/FBSD,  
>>>>>> OS-X, I-OS, Android). You need to think about both browsers  
>>>>>> and mail clients. Each of those come from a half dozen sources  
>>>>>> on each platform. Then you have configuration options on each.  
>>>>>> That's a lot of combinations.
>>>>>>
>>>>>> Each combo seems to have a different idea of what not to do  
>>>>>> when they see a self signed cert. If you want to be able to  
>>>>>> handle all of them, even "real" certs may have issues. There  
>>>>>> are indeed several common combo's that are a major pain with a  
>>>>>> self signed cert.
>>>>>>
>>>>>> No, I didn't write any of the code with the problems in it. I  
>>>>>> also don't want to get into the details of what and where.  
>>>>>> This really isn't the forum for that sort of thing. I'm not  
>>>>>> out to bash any particular solution, only to point out that  
>>>>>> there are indeed issues.
>>>>>
>>>>> Do handle part of the mess, we have setup our local root cert  
>>>>> at the computer club, and then sign our server certs to that. I  
>>>>> did a major overhaul on the infrastructure for that. It is  
>>>>> still not "real" safety routines, but ah well. We provide a  
>>>>> cert download which quickly solves the cert issue with most  
>>>>> browser.
>>>>>
>>>>> Seems to work for our myriad of server and client OSes and  
>>>>> clients.
>>>>>
>>>>> There is various ways to get "real" root certs, but depending  
>>>>> on degree of uhm... safety... it may be argued of their  
>>>>> capabilities. There is efforts to build a chain of trust for a  
>>>>> stable free root cert, but it is so far nog included in any  
>>>>> major browsers.
>>>>>
>>>>> Essentially it's a mess. I'm only scratched the surface here.
>>>>>
>>>>> Cheers,
>>>>> Magnus
>>>>>
>>>>> _______________________________________________
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>>>>
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>>>
>>>
>>>
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