2009/8/15 steve heidmann <[email protected]>: > > Hi Burt , > > Two thousand years ago the Wobulator was invented . An early sweep generator !
Was that one of the first miracles? 73, Steve > > 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. > -- Steve Rooke - ZL3TUV & G8KVD A man with one clock knows what time it is; A man with two clocks is never quite sure. _______________________________________________ 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.
