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, [email protected] <[email protected]> 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 > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
