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

Rob Kimberley rk at timing-consultants.com
Mon Oct 18 02:24:01 EDT 2010


FWIW,

I have my antennae in the house under the roof space. No problems with SVs.
As long as you have a clear view South (or North if you are south of the
equator) you should be OK. Usual things to check also  are cable length/type
and attenuation based on the gain of the antenna used.

Rob K

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Camp
Sent: 17 October 2010 16:09
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] New (refurbished) LPRO-101 GPSDO

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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