>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.
