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bg7tbl gpsdo master reference

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Electro Fan:
Hi Ringmodulator,

Thanks for your comments, I appreciate it.  I read a number of your earlier posts and they have always been helpful - Thx!

Your comments motivated me to run a few quick tests as shown in the attachments.

If you or anyone else would like to see some other tests let me know.

Part 2: with attachments

Electro Fan:
Ok Ringmodulator, you have made me move around from what was a comfy spot in the rabbit hole and now I am rethinking and retesting lots of stuff.

I happened to have in inventory a second BG7TBL GPSDO with the same date:  2018-06-05.

So I connected both with almost exactly the same cabling (except the BNC to SMA adapter for one channel) to the BG7TBL counter inputs - using just the counter's internal ref.

I ran GPSDO 2 over night so it accumulated more reads than GPSDO 1 (but GPSDO 1 was on over night and warmed up).

Results show pretty similar average readings to within ~0.17 Hz of 10 MHz (and to within ~0.003 Hz of each other on 10 MHz).

So, given the new rigor that your post prompted, I think all we can say is that these two BG7TBL GPSDO's are performing pretty similarly.  They both use the same model antenna with the same antenna cabling.  The antennas are next to each other (about 3cm apart) facing the sky (somewhat obscured by tree branches).  The signal strengths are not real strong - both GPSDO LCD indicators generally show only 1-2 bars due to the tree branches.  I attached the Sky View and SNR table below.

I also dug up an Oscilloquartz Star 4+ GPSDO that I will test as soon as I get a cable that will duplicate the cabling of the BG7TBL antennas but some preliminary testing shows the Star 4+ ref output is not so similar to the two BGTBL GPSDOs - but it might not have been fully warmed up.

I'd like to figure out what is the most accurate clock source but I'm not sure yet how to determine that - I'm open to any test configs you or others might suggest.

My current thinking is that while it's hard to know exactly how long a Hz should be, I might have to accept that close enough will have to be good enough; but even more so, I think I'd like that whatever the best Hz is, I'd like it to be the same across all my devices.  Kind of like maybe my ruler isn't perfect but at least I'll have a consistent unit of measurement when measuring, building, and testing things.

Electro Fan:
https://www.livescience.com/space/the-sun/the-2024-summer-solstice-will-be-the-earliest-for-228-years-heres-why

wouldn’t want to be late for anything :)

Electro Fan:
fwiw, I have the Oscilloquartz Star 4+ GPSDO running - providing both the input signal and the Ref in to the counter.

When compared to the BG7TBL doing the same thing, the Star 4+ holds it's own with pretty similar results. 

I've tried various combinations of tests (some posted here and above, and others not posted) and I can't quite figure out how to isolate what's what.  Seems like it should be simple but so far it hasn't become clear to me.   |O

I'm now of the opinion (just guess) that the Agilent generator by itself might possibly be accurate to within about 1-2 Hz on 10 MHz (even though the spec says approx +/- 1 ppm).

I think the BG7TBL counter is more accurate than the Agilent generator but that's also a guess.

I'm pretty sure that the 3 GPSDO's are the most reliable reference clocks, but again it's just a guess.

Comments, questions, and especially suggestions welcome.  Thx

---

https://en.wikipedia.org/wiki/Segal%27s_law

"From Wikipedia, the free encyclopedia

Segal's law is an adage that states:
A man with a watch knows what time it is. A man with two watches is never sure.[1]

At surface level, the adage emphasizes the consistency that arises when information comes from a single source and points out the potential pitfalls of having too much conflicting information. However, the underlying message is to question the apparent certainty of anyone who only has one source of information. The man with one watch has no way to identify error or uncertainty."

History
The saying was coined by the San Diego Union on September 20, 1930: "Confusion.—Retail jewelers assert that every man should carry two watches. But a man with one watch knows what time it is, and a man with two watches could never be sure." Later this was — mistakenly — attributed to Lee Segall of KIXL, then to be misquoted again by Arthur Bloch as "Segal's Law".[2]"

Electro Fan:
Next...

Here is the Agilent generator using it's internal oscillator providing a 10 MHz signal to the counter with the counter taking Ref from the Star 4+ GPSDO. 

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