[time-nuts] Spec An for phase noise measurements

John Miles jmiles at pop.net
Mon Jan 21 15:54:21 EST 2008

> > As a more-concrete answer to your question, since you mentioned
> a need for
> > coverage into the 6-GHz region, an 11729B/C and 8662A would
> actually be a
> > good choice.  Together they'll still be much cheaper than the 8561E I'd
> > recommend otherwise.  Figure $2500 at most for the 8662A and
> $1200 at most
> > for the 11729B/C.
> That's where you lose me -- the 8662A only goes to 1.28 GHz, right?
> Do you use multipliers?

Yes; that's the rest of the stuff in the 11729 box.

There are two rather-large caveats with the 11729.  First, make sure the one
you buy has all the microwave filters.  All of the labels in the buttons
should be populated.  When it was new, customers could save a lot of cash by
specifying "options" that deleted some of the filters, or all but one of

Second, you need to add a ~2 MHz low-pass LC filter to the LNA input.  By
default the LNA path has a 20 MHz LPF to allow flat response for offsets up
to 10 MHz.  That effectively keeps you from being able to measure sources at
10 MHz or less, because the other sideband coming out of the quadrature
mixer is at 2x the carrier frequency, and if that sideband leaks into the
LNA it degrades the accuracy at baseband.

There are 8662As available in the $1500 range, but most of them are kind of
ratty.  IMHO it's best to buy two of them anyway, so you have a parts mule
for troubleshooting.  They can be temperamental.  Plan on spending $2000 for
two beaters, or $2500-$3000 for a really-nice one.  Look for option 003, for
use with an 11729B/C.  You can add this option yourself but it's just
something else to deal with.

There are 11729B/C boxes available in the $3000 range, but that's overpriced
in my opinion.  $800-$1500 is more like it.  They are not all that rare.
Something like eBay item #120168988485 would be fine.

-- john, KE5FX

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