[time-nuts] Re: HP 10811A vs 10811-60111

David Kirkby david.kirkby at onetel.net
Sat Apr 23 18:11:00 EDT 2005

Tom Van Baak wrote:
> The seller should give you the 10811A that you
> bid on and won.

That's my feeling too.

To be fair, I received the oscillator yesterday and highlighted the 
issue to him today. He has already replied. His reply was

* David

* Please let met know.Have you tested the unit and
* confirmed that it is lower quality. I have sold these
* to other people and have not received any complaints.
* I have sold other oscillators taken from the exact
* type HP instrument. I'm sure HP would not put
* oscillators with different inferior specifications in
* the same model instrument. Let me know how your
* testing goes also tell me the exact
* specifications you are describing.

* Ray

So we have not hit a brick wall in our discussions. I've sent him the 
detailed specs of the two oscillators, and highlighted the differences 
and are awaiting his response.

The problem is the shipping costs on this are not insignificant, as the 
seller is in the USA and I am in the UK. I don't see why I should incur 
any costs for transportation of a unit that is not what I won.

Should I have chosen to return under his 5-day return period for some 
other reason (it was too large, not what I wanted), then of course I 
would expect to pay shipping costs both ways. But in this case I don't 
see why I should pay for someone elses mistakes. He has messed up - not me.

> In general there is a difference between a 10811A
> and a 10811-60111. The 10811A meets all the
> specs on the data sheet and the 10811-60111
> has relaxed specs. These -60111 are often found
> in medium performance frequency counters such
> as the 5328A where some of the 10811A specs
> have little or no relevance.

Yes, I see your point, although I want this as part of a local standard 
and will GPS lock it. Hence I can't say exactly what it will be used 
with, although the HP 5370B is an obvious candidate. But there will be 
other equipment too. Since I want it to be a standard, I want the best 
phase noise I can get. For that, the 10811A seems the most obvious 
choice, for its performance/cost ratio.

I suspect to get the best from a 5370B, the phase noise on the internal 
oscillator should be as low as possible.

> My guess is rather than design multiple OCXO
> types, HP designed one really good one and then
> used the results of manufacturing performance
> tests to determine which units should go to into
> which products.

Yes, that is my feeling. I suspect they were selected, and the better 
units were marked with the A and put into the more demanding applications.

> For example, it would be a waste to put a 10811
> with well above average phase noise performance
> in a frequency counter that only needs an OCXO
> for a precise 1 second gate.


> I suspect most other companies do the same for
> high-end OCXO.

Yes, it would make sense. Put the better units into the more demanding 

> This is not to say the 10811-60111 that you have
> is bad; nor that the 10811A that you should have
> received is guaranteed to be better. 

No guarantees, but there is a higher probability the 10811A's 
performance will be better.

> These are old,
> surplus oscillators and a lot can happen in the 20
> or 30 years since they came off the manufacturing
> line. I've seen some -60111 that test really well
> and some 10811A that are in really bad shape.

Your graphs at http://www.leapsecond.com/pages/z3801a-osc/ clearly show 
a wide range of performance of the same HP oscillators, but one might 
reasonably expect an oscillator that started life in better shape has a 
higher probability of being in better shape now - but as you say, there 
are no guarantees.

> If you're a bottom feeder in the surplus oscillator
> market like the rest of us 

I am - less so than you!!

> the only way to know
> the performance is to test what you get for the
> few parameters you're interested in. 

Unfortunately, I don't at this minute have anything to test it against. 
I have a 2.2GHz Anritsu spectrum analyser at work that is about 8 years 
old. The performance of that is possibly worst than either oscillator, 
so I would have no confidence of being able to measure the  HP 10811A or 
10811-60111 with that and come to any sensible conclusions.

I should have a 5370B here soon, but again, I am not sure of its 
oscillator's current performance - it will I think be an 10811A, but you 
know far more about that than me.

> A few eBay
> sellers do performance tests (such as accuracy
> or drift rate) but most sell as-is.

Well I bought it knowing there were no specific tests done on it, other 
than it has a 10MHz sine output. Of course I am well aware it might not 
meet its original specification due to aging of capacitors, crystal, 
resistors etc. I'm not blaming the seller for that.

But I did think the part number would be what I won, especially after 
confirming this with the seller and sending an email indicating I 
specifically wanted the 10811A.

Dr. David Kirkby

> /tvb
> ----- Original Message -----
> From: "David Kirkby" <david.kirkby at onetel.net>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Saturday, April 23, 2005 09:38
> Subject: Re: AW: [time-nuts] HP 10811A vs 10811-60111
>>Thanks for that.
>>It does seem the specification of the 10811-60111 is poorer than the
>>10811A, as the formers time domain stability at 1s is twice as bad
>>(10^-11) compared to that of the 10188A (5x10^-12), and just about every
>>other parameter is "not specified" on the 10811-60111.
>>It is particularly annoying when I has some suspicions it was not an
>>10811A, so asked the seller
>>and he confirmed it was, and then said I could have an 10811-60111 if I
>>wanted for the same price. I made it clear I did not want it, so he
>>sends me it anyway!
>>I sent him a mail saying:
>>"I have sent you payment for this. Please ensure it is the HP10811A and
>>not the HP10811-60111, which you said in an email you also had"
>>So he sends me an HP10811-60111 anyway!
>>Dave Kirkby
>>Hubert v. Bonhorst wrote:
>>>Sorry for page flipped. Attached pdf is for 10811-60111
>>>Best regards
>>>-----Ursprüngliche Nachricht-----
>>>Von: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] Im
>>>Auftrag von David Kirkby
>>>Gesendet: Samstag, 23. April 2005 16:32
>>>An: Discussion of precise time and frequency measurement
>>>Betreff: [time-nuts] HP 10811A vs 10811-60111
>>>Can anyone tell me the difference between the two above oscillators? I
>>>have the manual for the 97page manual (page 2 is upside down), but it
>>>does not mention the latter.
>>>However, I think I have seen a small couple of page document somewhere
>>>which listed the 10811-60111 as having no specification for phase noise,
>>>and so therefore not an ideal choice for a low phase noise oscillator.
>>>One might as well start with something that is specified for a low phase
>>>I can't however now find the exact spec of the 10811-60111. Can anyone
>>>give me it?
>>>I won an auction for a 10811A on eBay and the seller said I could have a
>>>10811-60111 for the same price if I wanted it too. I said no, I wanted
>>>the 10811A, but he has sent me the  10811-60111 instead.
>>>Is the 10811-60111 inferior? How does it differ from the 10811A?
>>>time-nuts mailing list
>>>time-nuts at febo.com
>>Dr. David Kirkby,
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Dr. David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

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