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Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !

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JBooth:
Okay, here are some pictures.

I don't see anything obviously wrong.  The solder joints on some of the SMD capacitors could be better, though. 

Is the 10.000 MHz crystal (Y1) just a clock crystal for the Atmel Mega 328P microcontroller?  Why would they use a 10 MHz clock crystal for a microcontroller that is supposed to be controlling a precision 10 MHz oscillator just on the other side of the board???  Wouldn't it be better to use a crystal clock frequency significantly different enough to avoid inducing interference into the precision oscillator?
Maybe that is the cause of some of the jitters and noise that is being picked up.(?)


Edit:  That capacitor "scabbed on" between U1 and R2 sure is ugly looking! 
But it looks like they got that add-on capacitor soldered in straight on the unit that Hans_18T has.

Dimitris:
Here are some picture of mine. I just got it off ebay.
The pcb looks a bit revised (2018-11-24) compared with the previous ones.
The date on the back panel reads  2019-02-28

note: U5 is not populated...  who knows...


eb4fbz:

--- Quote from: jeffsf on January 13, 2019, 04:06:35 pm ---
--- Quote from: Electroalice on October 15, 2018, 02:01:17 am ---The 10 MHz is good but the 1 PPS has a constant jitter approx. 20ns. Every 1 second it shifts 3  ns then on the 6th second jumps back and repeats continuously.

--- End quote ---

Good to know about the behavior of the PPS output. I'm not sure I'd call it "jitter" as it sounds like it's deterministic in behavior.

Might be similar to, for example, the Trimble Resolution T timing GPS that uses a 12.504 MHz internal clock and the PPS output is always coincident with an edge of that clock. See page 34-35 (36-37 of the PDF) of Resolution T GPS Embedded Board.

Edit: Checking https://www.u-blox.com/sites/default/files/products/documents/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf shows a 21 ns granularity in the "timepulse" signal of that unit, used in several of the BG7TBL units, from what I've read in the "master thread" (linked above).

--- End quote ---

Almost all GPS receivers have this PPS error. It's called quantization or sawtooth error, and it's due to finite pulse time generation resolution. Some special timming receivers report this deviation so you can correct your calculations or compensate using delay lines.

Leo Bodnar:

--- Quote from: jeffsf on January 13, 2019, 04:06:35 pm ---Good to know about the behavior of the PPS output. I'm not sure I'd call it "jitter" as it sounds like it's deterministic in behavior.

--- End quote ---
There is nothing wrong with deterministic jitter.
Leo

Val:
Hi Leo,

Sorry to disturb you.
May be I have missed similar discussions.
My device worked fine for about a year, but now it does not lock anymore.
I have tried three antennas, all the same.
Which voltages, signal form/shape I should check to find a fault?
Yours advice will be very much appreciated.

Val.

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