[time-nuts] Phase noise from Allan Deviation ?

[Mark Spencer]

Yes.   I was not overly pleased with the performance of my 2700's.   I ended up pulling the PRS10 out of one of them and purchased the breakout connector board from SRS and used the resulting 10 MHz and 1 PPS outputs.    From time to time I would sync the unit to one of my GPSDO's using the 1 PPS input.

I haven't powered up my 2700's in several years.


Your mileage may vary.


> On Dec 14, 2015, at 1:10 PM, Bob Camp <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> One of the reasons the TS2700’s went out of favor is the “quality” of the CDMA signals 
> available. The design assumption was that the CDMA carriers provided timing as good 
> as GPS on their over the air systems. After the units had been in the field for a while it
> became apparent that the 2700’s were not performing up to expectations. Further investigation
> turned up a range of issues that degraded the CDMA timing relative to GPS. A lot of it 
> boiled down to “we are a phone service not a time service”.  System wise, CDMA gets 
> into trouble at the 10us level. GPS is in trouble at the 100 ns level….
> 
> Yes there are all sorts of rules and regulations. In the end it’s “this works fine” that trumps
> a lot of them. 
> 
> Bob
> 
>> On Dec 14, 2015, at 1:15 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
>> 
>> Tom wrote:
>> 
>>> The 'unknown' is a Rubidium oscillator locked to CDMA pilot (TS2700)
>> 
>> There is very little information publicly available on the Symmetricom "BesTime" engine ("BTE"), but after playing with a few TS2700s for quite some time, including monitoring a number of internal signals, several things became apparent.  First, the 2700 does not seem to discipline the PRS10.  The rubidium runs open loop and the BTE keeps track of the offset and the drift rate from "BTE time" (which is synthesized from all available sources -- however many CDMA signals it is receiving, plus any wireline telco timing signals and the PRS10 -- using a proprietary algorithm to estimate the reliability of each source and outputting BTE time and frequency using DDS).  Hobby users won't be feeding the unit any telco timing signals, so the BTE has only the CDMA signals to work from.  During holdover (and assuming no telco timing signals), the Rb is the sole input to the BTE, which uses the stored offset and drift to calculate BTE time.
>> 
>> I found that the TS-2700 is more than an order of magnitude less stable than a Trimble Thunderbolt, even with a full complement of rock-solid CDMA sources.  This may vary somewhat, depending on the CDMA equipment in use at any particular location and the diligence of the CDMA operator.
>> 
>> Best regards,
>> 
>> Charles
>> 
>> 
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