[time-nuts] YIG oscillator drift question

ed breya eb at telight.com
Sat Dec 8 22:41:29 UTC 2012

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.


More information about the time-nuts mailing list