[time-nuts] Two types of GPDSO / Rubidium

[Taka Kamiya]

Tom,
I know you are absolutely right.  When I buy from eBay, I have no idea where they came from.  Reject pile, junk yard, or pristine clean room.  Unfortunately, I can afford up to certain amount.  I have lots of PRS10 but their origin is unknown.  Even if I buy 5065A, origin will be unknown and so as condition.  Recently, I called around local cal-lab to see who can help me validate these devices.  No one could.  I'm very tempted to buy T-bolt or PRS10 new but at $1500, it's quite hefty.  I may just have to.
I'm at learn as much as I can stage.  I have a Cesium but it's old.  4040/A  I have no idea how it was used or stored.  It would be nice to have one known good standard.  The best I can do for now is my array of GPSDOs.  (from unknown sources)

--------------------------------------- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

    On Thursday, September 26, 2019, 3:05:19 AM EDT, Tom Van Baak <tvb at LeapSecond.com> wrote:  
 
 It might be a bit of an over-simplification to split oscillators in 
those two camps, "fixed" and "agile". There are often many trade-offs in 
performance that you have to deal with. Moreover if you are getting your 
oscillators from eBay, or especially parts from China, you may also have 
to assume that original factory specs are no longer valid.

This is one reason why the time nuts list is so preoccupied with making 
accurate measurements of frequency standards. You only know what you 
have if 1) you buy it new from a reputable company, or 2) when you buy 
it cheap and measure it yourself with reputable test equipment, or 3) 
you get it from a friend who has measured it for you.

If you're asking specifically about Rb, I think the data shows that hp 
5065A has best performance, followed by PRS10, followed by all the cheap 
telecom Rb. Sorry, I don't have plots or URL's handy at the moment to 
support this with real data. My main take-away is to start with your 
requirements, see which products / specs meet that, and if you're buying 
dirt cheap surplus, make your own measurements to validate your 
requirements.

/tvb


On 9/25/2019 3:45 PM, Taka Kamiya via time-nuts wrote:
> This is a cross post from EEVBLOG.  I'm hoping there is someone who's familiar with this subject would help me out here.
> I am hoping someone can help me understand this.  I've seen similar discussions take place both for GPSDO with Crystal Oscillators and Rubidium modules.  It appears there are two types of each.
> 1)  fixed frequency type (less jitter)
> 2)  frequency agile type (more jitter)
>
> I've read frequency agile Rb modules (ones you can change output frequency) is one kind of Rb (sa.22c and fe5650, etc), and there is another one that you cannot change frequency. (ie. T-bolt, PRS10, etc).  Words like phase noise and PLL are thrown out often in discussions.  I vaguely remember frequency agile types are less suitable if ultimate in stability is needed such as multiplying the output into GHz range.  This discussion was about 10GHz transverter.
> Is this because frequency agile type has the ultimate output from PLL (subject to jitter) and fixed frequency type is from OCXO?  If this is the case, why frequency agile type even exist?  It's not like it can be used as a VFO (on radio).....
>
> I'm sorry this is SO vague but that's the reason for this post.  I need to understand this.  There was a wiki page on this, but it doesn't go into this discussion deep enough.
>
> Would someone help me gain knowledge in this?
>
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
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