[time-nuts] Re: HP 10811-60111 Oscillators {External}

[Bob Camp]

Hi



> On Jan 11, 2023, at 1:05 PM, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> On 1/11/23 8:55 AM, Bob Camp via time-nuts wrote:
>> Hi
>> 
>> There always has been a pretty wide range of ADEV’s on the 10811’s. One of the fun things
>> they did at Santa Clara was to screen them for ADEV. Once they found enough “good ones”
>> for that month, they stopped screening. The ones that made the grade got this or that part number
>> sufix on them and headed into gear that needed them.
> 
> 
> Cherry picking oscillators is a "standard thing" (although one that you hope you'd not have to do).
> 
> My project is in the middle of looking at oscillators in an X-band transmitter for phase noise/short term ADEV.
> 
> It turns out that DSN only has narrow symbol loop bandwidths (up to 25 Hz) and these transmitters (2 Mbps) weren't designed with that in mind, so they'll lose symbol lock occasionally. In a 400 Hz loop bandwidth there's no problem.   But DSN was designed and built for 10 bits/second, insanely tight loop bandwidth to get the noise down.
> 
> And, of course, it's just on the ragged edge.  Some work, some don't. Of course, the crystal mfr (I have no idea who it is, that's 3 subcontract tiers down) probably doesn't specify anything - maybe they have an overall jitter spec with some wide bandwidth.  And all the usual things - how do you measure it without opening up the transmitter? How do you set up a test jig? What is the "real requirement"?
> 
> Had we realized this earlier, it's conceivable we could have flowed a requirement down to the radio mfr, who would then flow that to the board designer, who would flow that to the crystal company.  And turn $20 crystals into $2000 crystals, because the mfr would probably have to do the cherry picking, and the yield would be terrible. (Of course, they could sell the other ones per usual, but when you're ordering 10-20 crystals, and you have to screen 1000 to get the good 10, it might not be worth even saving the ones that don't make the cut. They're now out of the usual flow.
> 

…. it’s worse …. a lot worse ….

If the parts are destined for space, each and every step along the way, they get a pile of paperwork.
There are lots of steps and thus lots of paper. It starts back at blank cutting ( if not at quartz growing) 
and moves forward from there. Each one is part of a group and the group gets paperwork as well. 
Pretty quickly, you have a $2 blank and $20 in paperwork for that specific blank.  That paper just keeps 
piling up as it turns into a finished crystal. 

Decide to screen a hundred crystals to find the best 1%? Unless the rest are going into space as well,
all that paperwork heads to the scrap pile. Even if they *are* headed to space, that’s a whole lot of 
crystals. You better have a high volume customer to push them off on. ( good luck with that ….). 

Since a crystal is pretty unique, both the custom guy and the high volume guy would need to be buying
a *very* similar end product. Obviously, a frequency change is a killer. A temperature range change 
may well be. Shock / vibration / warmup / pull range ….. any one of those *might* kill the swap. 

If you want to keep accounting happy, both the screen outs and the rest need to head out the door 
pretty close to each other. The days of "put it in inventory and hope” are long gone. ( and for good
reasons ….. tons of those inventory crystal eventually went to the dumpster). 

Bottom line is that if you screen 100 to get 1, in this case, you pay for the 100 …..

Bob


> Another strategy would be for the radio mfr to make lots of boards, with crystals as they come, and sort those.  That might actually be cheaper - I'll bet the "as mfr" cost of the boards is <$150, which is a lot less than $2000. and the "reuse" is easier.
> 
> This whole oscillator business is MUCH more complicated than a lot of people think.
> 
> 
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