Re: Magnetic Field in a Flat Spiral

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

It appears the humidity is probibly changing the dialectric constant and the
resistance of the air. In a flat coil you are subject to the capacitive
effects of the surounding air in both I and E aspects of the air return
capacitive aspects of the surounding field. While the temprature is changing
the L of the coil itself (expansion and contraction of the coil) this effect
should be low.Tesla found that temprature had a great effect on the tuning
of a flat coil This should NOT have a great effect on the Q of the coil its
self, only the tunung curve. Each test should have corrected for this.
  Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Sun, 10 Mar 2002 20:28:44 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: Magnetic Field in a Flat Spiral
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Sun, 10 Mar 2002 20:29:55 -0700
> 
> Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <m.j.watts-at-massey.ac.nz>
> 
> Hi Jim,
> 
> On 10 Mar 2002, at 17:23, Tesla list wrote:
> 
>> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
>> 
>> The variation in resistance just due to temperature might have a significant
>> effect on Q, even though the temperature variation isn't much. Let's see...
>> tempco of copper is something like 0.004 per degree (C).., I think.  A 10
>> degree change will result in a 4% change in DC resistance...  It will also
>> affect the skin depth, so the effect might be more than that....
>> 
>> It might also be 0.0004, in which case, we're looking at fractions of a
>> percent..
> 
> Yes, but doesn't copper have a positive tempco? In which case, had
> that been the influencing factor, I should have scored a higher, not
> lower Q on the second day? And if that's so, then humidity appears to
> be having a greater effect than I had previously suspected?
> 
> Regards,
> Malcolm
> 
>> ----- Original Message -----
>> From: "Tesla list" <tesla-at-pupman-dot-com>
>> To: <tesla-at-pupman-dot-com>
>> Sent: Sunday, March 10, 2002 2:28 PM
>> Subject: Re: Magnetic Field in a Flat Spiral
>> 
>> 
>>> Original poster: "Malcolm Watts by way of Terry Fritz
>> <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
>>> 
>>> Hi Paul,
>>> 
>>> On 7 Mar 2002, at 17:06, Tesla list wrote:
>>> 
>>>> Original poster: "Paul Nicholson by way of Terry Fritz
>>> <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
>>>> 
>>>> David Thomson wrote:
>>>>> what is the formula for calculating the Q of a coil by taking the
>>>>> two voltages on either side of the resonant frequency?
>>>> 
>>>> Detect the coil's resonance with a distant pickup, or by measuring
>>>> the base current.  Turn down the output of your signal generator so
>>>> that it is below half of its maximum drive voltage. Tune the signal
>>>> generator for a maximum reading on your detector and mark this level.
>>> <snip>
>>> 
>>>> A signal generator with a good fine tune is a prerequisite, as is a
>>>> frequency counter.  You need to make sure that the drive voltage can
>>>> be turned up by exactly a factor of two at the coil base. Use a sine
>>>> wave drive voltage.  Even with care the method might only be 5% or 10%
>>>> accurate due to the sensitivity to the small difference |f1-f2|.  Day
>>>> to day variation of the Q is to be expected, for reasons which remain
>>>> unexplored, I think.
>>> 
>>> During a series of precision Q measurements I detected a variation
>>> between one day and the next of 6 - 7% in a moderately large
>>> resonator. The most notable difference between the two days was
>>> humidity. The air temperature on the day that the coil came in lower
>>> was also down somewhat - maybe 3 - 5C.
>>> 
>>> Regards,
>>> Malcolm
>>> 
>>> 
>>> 
>> 
>> 
>> 
>> 
> 
> 
> 
>