[time-nuts] Coil sensitivity to external magnetic fields...

[steve heidmann]

 Hi Burt ,

Two thousand years ago the Wobulator was invented . An early sweep generator !

                                              Steve

--- On Fri, 8/14/09, Burt I. Weiner <biwa at att.net> wrote:

From: Burt I. Weiner <biwa at att.net>
Subject: [time-nuts] Coil sensitivity to external magnetic fields...
To: time-nuts at febo.com
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.
biwa at att.net
K6OQK 


_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.