[hpsdr] GPS 1PPS board

[John Ackermann N8UR]

I'd put it a little differently:  the 10kHz signal does not make it 
possible to get *better* performance than a GPS with a 1 PPS signal, but 
it allows much simpler circuitry since filtering a 10 kHz signal is much 
easier than filtering 1 PPS, particularly if using analog components.

However it's important to realize that the GPS part of any GPSDO affects 
only the long term frequency stability.  When measuring over time 
periods shorter than around 1000 seconds, the performance of the XO is 
paramount.  One of the problems with building a cheap GPSDO is that good 
XOs are expensive, and therefore the short term stability is pretty much 
  tied to the builder's budget or scrounging skills.

The control loop should (a) optimize the "cross-over" point where the XO 
stability matches the GPS system stability; and (b) avoid messing up the 
short term stability through excess noise applied to the XO's tuning 
voltage.

John
----

Henry Vredegoor wrote:
> Hi John, All,
> 
> Thank you John for your quick answer!
> 
> So this unit is not particularly suited for high precision frequency
> control, even when used with the 10KHz output signal.
> 
> Thinking of getting into precise frequency control for HPSDR, are there
> other surplus GPS's currently available, better suited for frequency control
> in the opinion of this forum, besides the Motorola Oncore UT+ mentioned by
> Graham?
> 
> 73,
> 
> Henry.
> 
> 
> 
> 
>> -----Original Message-----
>> From: John Ackermann N8UR [mailto:jra at febo.com] 
>> Sent: maandag 6 april 2009 20:50
>> To: Henry Vredegoor
>> Cc: 'Graham / KE9H'; 'Chris Salinas'; 'HPSDR discussion list'
>> Subject: Re: [hpsdr] GPS 1PPS board
>>
>>
>> It's a bit of a mix.  The 10 kHz signal is derived from the 
>> GPS' onboard 
>> oscillator which free-runs.  Once per second, the 10 kHz is "jerked 
>> back" to alignment with the PPS signal (the receiver computes 
>> only one 
>> timing solution per second).  So, over time it gives the same 
>> performance as the PPS.
>>
>> John
>> ----
>>
>> Henry Vredegoor wrote:
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>>
>>> Hi Graham, All,
>>>
>>> Is the jitter spec specifically for the 1pps signal only or 
>> does this also
>>> apply to the 10KHz output?
>>> (I could imagine these being "coupled", the 1pps signal 
>> being derived from
>>> the 10 KHz, so it would apply for both)
>>>
>>>
>>> 73,
>>>
>>> Henry.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: hpsdr-bounces at lists.hpsdr.org 
>>>> [mailto:hpsdr-bounces at lists.hpsdr.org] On Behalf Of Graham / KE9H
>>>> Sent: maandag 6 april 2009 18:12
>>>> To: Chris Salinas
>>>> Cc: HPSDR discussion list
>>>> Subject: Re: [hpsdr] GPS 1PPS board
>>>>
>>>>
>>>> ***** High Performance Software Defined Radio Discussion List *****
>>>>
>>>> Chris:
>>>>
>>>> Although a cheap way to get started, this is a navigation 
>>>> receiver, not 
>>>> a timing receiver,
>>>> and it will not be a good choice for frequency control.  This 
>>>> one's spec 
>>>> is that the 1 pps
>>>> signal has a jitter spec of +/- 1 microsecond.  Timing 
>>>> receivers, such 
>>>> as the Motorola
>>>> Oncore UT+ have a timing mode, that provides jitter around +/- 50 
>>>> nanoseconds,
>>>> without sawtooth correction, and sub 10 nanoseconds with sawtooth 
>>>> correction.
>>>>
>>>> You want a timing receiver, or a receiver with a timing mode 
>>>> option for 
>>>> frequency
>>>> control.
>>>>
>>>> --- Graham / KE9H
>>>>
>>>> ==
>>>>
>>>> Chris Salinas wrote:
>>>>> Hi All,
>>>>>  
>>>>> With Excalibur being designed, a good 10Mhz time-base is needed.
>>>>>  
>>>>> I came across (on Ebay) a Rockwell Jupiter board that could 
>>>> be used in 
>>>>> an accurate 10MHZ source.
>>>>>  
>>>>>
>>>> http://cgi.ebay.com/Rockwell-Jupiter-12-channel-GPS-receiver-O
>>>> EM-module_W0QQitemZ290306684157QQcmdZViewItemQQptZGPS_Accessor
>>>> ies_Cables?hash=item290306684157
>>>>>  
>>>>> Here's a manual I came across:
>>>>>  
>>>>> http://www.gpskit.nl/documents/rockwell/jupiter-gps-board.pdf
>>>>>  
>>>>> Pin 19 on this board has the 1 PPS signal, so I wonder what 
>>>> it  would 
>>>>> take to integrate it into Gibraltar or come up with a 10 
>> Mhz source 
>>>>> for Excalibur using this board.
>>>>>  
>>>>> There are over 900 boards from the source.
>>>>>  
>>>>> Chris N0TTW
>>>>>
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