[time-nuts] Modern Rb atomic reference vs classic Cs

Sat Mar 14 18:50:45 UTC 2020

Hi

Used Cs standards show up for a wide range of prices. Sometimes that $50
hamfest acquisition *does* turn out to be a working device. For most of us, most
of the time eBay is the source and you pay the “market price” there. Even there,
figuring out what that price *is* can be a chore. 

Best guess is that you are unlikely to get a working unit for less than $1,500 
delivered. There are a lot of listings at 2X to 5X that price level. Most of those 
listings do not provide a lot of “hope” for the device being in working condition. 
There are also a lot of listings below that price point for what appear to be gutted
chassis.( = no hope at all). You could easily go through more than one purchase 
before you get a unit that is still reasonably close to working a year or two later. 

There are brand new instruments like the FS 740 or FS 752 that are “in the same 
ballpark” as far as cost. (assuming you don’t get lucky first time). They come with 
nice things like warranties. Power, size, and feature wise they are pretty competitive 
compared to the eBay 506. 

Is any GPSDO “as good as” a 5071 with a high performance tube in it in all respects?
No, of course not. There will *always* be things the GPSDO falls behind on. There
are also standards running around places like NIST that do some things better 
than a 5071 with the fancy tube.

A brand new 5071 with that tube appears to be over $90,000 these days. Based on 
running one for a lot of years, After about 6 years of operation, you will be sending 
it back for a new tube. By the time the unit is back in your lab, the refit will cost 
roughly half the price the whole unit cost new …. gulp …..

Lots to think about ……

Bob

> On Mar 14, 2020, at 2:23 PM, Taka Kamiya via-nuts <time-nuts at lists.febo.com> wrote:
> 
> Paul and Bob are my valuable mentors, and I trust their opinion.
> I do have an old working Cs but my go-to are GPSDO.  For most part, it's more than sufficient.  I also have ex-telecom Rb.  There aren't too many things one of them can't do, except for measuring themselves.  In my lab, the "lab standard" is GPSDO and backup is Rb.
> At a hobby level, one of the big issue (at least to me) is power consumption, and the heat they generate.  My lab gets significantly warm.  Plus, instant availability of GPSDO and Rb (because they are always on) is hard to beat.  To save Cs, I only turn on mine when needed, then wait for 2 days.
> To be honest, I'd love to have an HP5071A with warranty.  But it's far beyond affordable range for me.  Also, a "standard" I can't trust isn't a standard.  I am not good enough to properly care for Cs and I don't have good enough measuring system.  It takes a lot to keep Cs happy and usable in many ways.
> Signed, on laziest ham.
> 
> --------------------------------------- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> 
> 
>    On Saturday, March 14, 2020, 12:14:43 PM EDT, paul swed <paulswedb at gmail.com> wrote:  
> 
> I will chime in here also. It is indeed great to say you have a cesium. HP
> 5061s are just good fun to play with. It teaches you that as much as you
> think you know you actually don't. But they do honestly take care and
> feeding especially in the tail-end market that i can afford.
> So to Bobs comment if you want a good reference for time-nuttery the GPSDO
> is a really effortless way to go. Hard to say if RB or Xtal is better it
> depends on what you might get at a flea market. But there is a lot to be
> said for turn it on and be happy. I actually run a GPSD-TCXO as a instant
> on sort of right there for my ham stuff. Power consumption sub 10 Watts.
> Then flip to a HP3801 or any number of alternates including Cesium for
> serious stuff like D-PSK-R development.
> Signed one lazy ham.
> Regards
> Paul
> WB8TSL
> 
> On Sat, Mar 14, 2020 at 8:31 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> Backing off a bit, as long as GPS is doing it’s part ( or your GNSS system
>> of
>> choice …) an OCXO based setup may do as well as / better than your typical
>> “almost dead” used Cs standard.
>> 
>> It is very easy to find a used Cs with a dead tube. It is quite hard to
>> find one
>> with a tube that is fully up to original specs / runs for years. Finding
>> replacement
>> tubes is ( and always has been) a very involved process. There are way
>> more
>> used / dead tubes out there than used / working.
>> 
>> Buying a new tube is in the “forget about it” price range. There also is
>> no practical
>> way to rebuild one. You can do this or that trick to maybe get a bit more
>> time out
>> of this or that tube … but maybe not.
>> 
>> Thus the pair of dead 5061’s sitting in the basement.
>> 
>> Bob
>> 
>>> On Mar 14, 2020, at 12:06 AM, Peter Membrey <peter at membrey.hk> wrote:
>>> 
>>> Hi guys,
>>> 
>>> Potentially a bit of a loaded topic, but I'm really curious as to what
>> the consensus is on this. For the research I've been doing over the past
>> few years, I've been predominantly using an SRS FS-725 (which uses the
>> PRS-10) disciplined by a Microsemi S650 (with the Rb option, though it
>> never went into holdover).
>>> 
>>> Modern Caesium references are expensive compared to the FS-725, but now
>> and then more classic Caesium references become available such as the HP
>> 5061A. These still aren't cheap (actually, not far off a brand new PRS-10)
>> so I was wondering how do they generally compare with a modern Rb?
>>> 
>>> If I have a PRS-10 that's being disciplined by a good GPS source, would
>> I see any benefit if I replaced the PRS-10 with an HP5061A (particularly in
>> terms of stability)?
>>> 
>>> Thanks in advance!
>>> 
>>> Kind Regards,
>>> 
>>> 
>>> Peter Membrey
>>> 
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