On 5/28/13 9:29 AM, Bob Camp wrote:
Hi
The cost of a BVA oscillator is primarily a function of the cost of the
blank used and secondarily a function of the resonator processing. You see
numbers in the $200 to $400 range tossed around for the blank (vs < $10 for
a good SC blank). The packaged resonator starts looking like $600 to $900
once you have that sort of blank in it (vs < $20 for a similar SC). BVA's
are never going to be cheap or plentiful.
I think you will find a number of people selling 5 MHz OCXO's in the -110 to
-120 dbc/Hz at 1 Hz range. That's not really where the BVA is needed. It's
benefit is more in the 0.1 or 0.01Hz phase noise. Put another way, ADEV is
the better tool to rate a BVA.
If you really want to get any resonator (or even an atomic standard) to look
good on ADEV at 1 to 10,000 seconds, it needs to be temperature stable.
Either it needs a really good oven, or you need a lab that doesn't change
temperature. For good ADEV in a normal environment, that means a "hockey
puck" style single oven, or a good double oven. Again, a cost adder /
greater scarcity thing.
Given all that, a BVA that gives you < 1x10^-13 from 1 to >1,000 seconds in
a normal lab is a very rare item. What ever the cost, it's going to be
pretty steep.
The USO's we got for GRAIL from APL have ADEV<1E-13 from 1 to 1000
seconds, and then heads up at 1 decade/decade. The lowest ADEV is about
5E-14 at around 50 seconds, but it's pretty flat. See the paper by
Enzer et al.
Or better, the 42ns PTTI conference paper by Greg Weaver at APL, who had
to build them.
They are space qualified, so they're fairly pricey (>$1M a copy). But
to put the discussion about blanks and finished product.. I think they
started around 1000 blanks to produce a few dozen packaged crystals,
which were then run as oscillators to see which ones were the best,
producing maybe four final pieces, 2 at each frequency.
The Weaver PTTI paper compares these to the BVA resonators.. SC cut
5MHz, 3rd overtone.
They run in a vacuum bottle (of course), and they have somewhat
obsessive attention to a lot of details. But I suspect that aside from
the space qual aspects, the whole "how you build them" isn't a whole lot
different.
Very much an art at many steps along the way. There are people at the
crystal houses who have been working on these things since the days of
Transit.
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