[time-nuts] YIG oscillator drift question

Peter Bell bell.peter at gmail.com
Sun Dec 9 04:02:00 UTC 2012

Another thing you should be aware of is that they have quite a bit of
hysteresis - so even with the same tuning current the output frequency
might differ by several MHz depending on whether you approached that
setpoint from above or below.  The YIG sphere also has a substantial
temperature coefficient - so although you don't *need* the heater in order
to get the oscillator working not having it will substantially degrade your
frequency stability.

On Sun, Dec 9, 2012 at 6:45 AM, iovane at inwind.it <iovane at inwind.it> wrote:

> >Yes, something must supply the minimum magnetic field to activate the
> >oscillator - but the current determines the field, so it's
> >necessarily part of the drift characteristic. It also depends on
> >whether the YIG sphere is heated - usually to 80 deg C or so, to help
> >stabilize it.
> >
> >Without any other frequency control, you can expect it to stay within
> >about +/- 10 MHz of the frequency predicted by its tuning curve. It
> >is very linear with magnetic field, hence tuning current, until the
> >core material begins to saturate at high flux levels, so the tuning
> >current needs to be increased to compensate.
> >
> >The most common type is one-octave 2-4 GHz, used in spectrum
> >analyzers from the 1970s on, and also the first microwave band of
> >many generators. Another common one is the 2-6.X GHz also used for
> >the same purposes, but covering a wider direct range. The next bands
> >up are typically 4-8, 6-12, 8-12,  and 12-18 GHz, used in generators,
> >at least in older gear. You can expect to find about +10 to +18 dBm
> >output power range, and fairly flat with frequency.
> >
> >The minimum setup is one or two power supplies, plus a variable coil
> >current driver up to one amp or so. You don't need the heater to run
> >it. Don't bother with the FM coil - it's not needed for basic
> >experimenting, and it's easy to burn out if you screw up. The main
> >coil is more robust, but it can be burned out with too much current,
> >so don't go too far beyond the maximum tuning current spec. It can
> >also shock you from inductive kickback, so the coil needs clamping
> >too. It's best study the circuits of existing sweepers and such to
> >get ideas on how it's all done.
> >
> >Your best bet is to get an old HP8620 or Wiltron 610 sweeper with
> >some plug-ins. They are simple enough to dig into the guts and
> >modify/experiment. These are regular old analog sweepers with no
> >synthesis - look at their specs to see what kind of stability can be
> expected.
> >
> >Ed
> >
> Ed,
> thanks for your advices.  Accuracy vs tuning current is not an issue for
> me,
> but stability does. I should experiment.  But I begin to understand that
> they
> are orders of magnitude far from even the worst crystals.
> Antonio I8IOV
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