Hi Burt , Two thousand years ago the Wobulator was invented . An early sweep generator !
Steve --- On Fri, 8/14/09, Burt I. Weiner <[email protected]> wrote: From: Burt I. Weiner <[email protected]> Subject: [time-nuts] Coil sensitivity to external magnetic fields... To: [email protected] Date: Friday, August 14, 2009, 6:52 AM Pardon me for inter-loping here - I don't know if this has any bearing on the subject but the following was certainly a learning experience for me. About a thousand years ago I had an ICOM IC-21A two-meter radio. The speaker coil opened and the only convenient replacement I could find had a larger magnet. The speaker for this radio is mounted in the lid. I replaced the speaker and checked it out before re-assembling the radio. Everything was fine. Once I re-assembled the radio it was deaf. Figuring I had bumped something I opened it up to check. With the lid off it worked fine. After a few rounds of this same exercise I decided I was going to put the lid on with the receiver operating. What I discovered was that the magnet on the speaker came within about 1/8" of one of the I.F. cans. The field from the magnet detuned the I.F. coil. I finally had to order a replacement speaker from ICOM, which solved the de-tuning problem because of the smaller magnetic. What I learned is that, depending on the resolution of your test equipment, yes, very small fields, A.C. or D.C. can impose a tuning effect on an inductor with a Ferris type core. A D.C. field can (shift) de-tune a circuit and an A.C. field will modulate it by changing the reactance of a Ferris type core inductor. Burt, K6OQK > Subject: Re: [time-nuts] OCXO sensitive to gravity > To: Discussion of precise time and frequency measurement > -1; format=flowed > > Bruce Griffiths wrote: > > Some caution is in order as some ferrites used in RF transformer coils > > may be permanently altered by application of a strong magnetic filed. > > Testing at lower fields first would be safer. > > Setupo a pair of Helmholtz coils and excite them with low frequency AC > > and look for associated sidebands in the oscillator output. > > NB a spectrum analyser is unlikely to be sensitive enough for this. > > I was just about to say the same. Also, it has much higher repeatability > and makes quality measures on measures and counter-measures much easier > to achieve. > > Cheers, > Magnus Burt I. Weiner Associates Broadcast Technical Services Glendale, California U.S.A. [email protected] K6OQK _______________________________________________ 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.
