[hpsdr] 1 pps GPS

[Phil Harman]

Hi Joe,

No Joe, you did not miss an announcement - we have not done this as yet!

Your error on  10m and 6m seems consistent with what others are seeing. 
The 10MHz TXCO on Penelope is intended to reduce any drift of the 
122.88MHz clock rather than being the last word in accuracy. There are 
multiple footprints for the TCXO on Penelope so one option would be to 
replace it with one of a higher specification.

If you have an external 10MHz reference you can feed that into the 
Altas bus on C16. Just see my recent post on this since you need to be 
aware of levels and keeing the signal clean.

We, well mainly John N8UR,  are presently designing a simple Altas 
board that will take an external 2.5/5/10/20MHz reference and enable it 
to be interfaced to C16. It will also have an adjustable tuning voltage 
so you can set an OCXO/VCXO on frequency or use an external GPS based 
locking device etc. John gave a presentation at Dayton last week on 
this in the TAPR forum - not sure if it was videoed or not. The board 
will have an external power connection so the oscillator/oven can run 
all the time if desired.

There is plenty of space left in the FPGA on Penelope so totally 
feasible to add code to lock the 122.88MHz VCXO to a 1pps reference. I 
expect we will need to make some serious modifications to the PLL 
filter currently fitted to Penelope but apart from that all the 
components are there.

I'm not sure if this is really a good idea since you really want to 
leave the 122.88MHz clock running all the time since otherwise the lock 
time could be quite long. Better to lock an external reference, that 
runs all the time,  to the 1pps signal and feed that into the Atlas 
bus.  There are others on the forum who have much more experience with 
such systems than I do so perhaps they would care to comment.

BTW, Bill KD5TFD made the observation yesterday that there is really no 
need to use 10MHz as a reference. Assuming a common factor between 
122.88MHz and the reference then we can lock them together.

73's Phil...VK6APH







Quoting Joe Martin K5SO <k5so at valornet.com>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> Phil VK6APH,
>
> I now have my A/J/O/Penelope boards up and running.  What a great set 
>  of boards these are!!  Congratulations to you and the various other  
> HPSDR team members and TAPR members in producing such a high quality  
> combination of boards!  Thank you from all of us!  This is a very  
> exciting project.
>
> With regard to Penelope I notice that the output frequency on mine is 
>  about 800Hz low at 28.01 MHz and 1.1KHz low at 52.01 MHz.  I have  
> noticed several mentions in the HPSDR docs about using a 1 pps GPS  
> signal to discipline the various oscillators but I have not seen any  
> details in the HPSDR docs about where/how that should/can be 
> inserted/ implemented.  Did I simply miss it somewhere?
>
>  Is using a 1 pps GPS a capability that is currently implemented or  
> is that a capability that is planned for future implementation?  I  
> currently have a Garmin GPS-25 1 pps signal available and would like  
> to use it on my HPSDR combo, is that something that I do at this 
> stage  of the HPSDR development?
>
> 73, Joe K5SO
>
>
>
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