[time-nuts] YIG oscillator drift question

[iovane at inwind.it]

>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