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

Steve Rooke sar10538 at gmail.com
Sat Aug 15 11:30:01 UTC 2009


2009/8/15 steve heidmann <steveheidmann at yahoo.com>:
>
>  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 <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
>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.



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