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Re: More inductor talk, Proximity effect, self capacitance

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On 9/28/2016 5:06 PM, amdx wrote:

>
> Try the figure again, it works for me.
>> http://i395.photobucket.com/albums/pp37/Qmavam/Close%20vs%20space%20wound._zpsctlfmjdi.png
>>
>
>
> But note: the coils have near identical Q's and then the spaced coils Q
> rises quickly, why didn't it just start out higher as it should have
> less loss because of less proximity effect. That only shows up at higher
> frequencies, why?
>
>                                 Mikek
>
>
  I think I found some ideas here.

> http://www.crystal-radio.eu/enlckring.htm

Where he says,

The Q factor of a unloaded LC circuit is determined by the following 
factors: series resistance in the circuit, parallel resistance across 
the circuit and magnetic losses.

The  series resistance in the LC circuit,
the lower the series resistance the higher the Q.

The total series resistance in the circuit (Rs) is the sum of:

The wire resistance of the coil, thicker wire or litzwire with much 
strands helps to reduce wire resistance.

The resistance of the capacitor plates, silvered plates gives the lowest 
resistance.
Plates with oxide gives more resistance than clean plates.

Contact resistance between rotor and frame of the variable capacitor, 
preferable the variable capacitor has a spring connected to rotor and 
frame, this provides a low resistance.
When the contact is made with a slidercontact at the rotor, this must be 
clean and free of oxide.



The parallel resistance across the LC circuit,
the higher the parallel resistance, the higher the Q.

Parallel resistance across the circuit (Rp) is caused by dielectric losses.

There are:
Dielectric losses in the coilformer
Dielectric losses in the insulation of the coilwire
Dielectric losses in the insulators of the tuning capacitor
Dielectric losses in materials placed near the coil or tuning capacitor, 
look  here for more information about this subject.
If the capacitor plates are not clean: dielectric losses in the dirt and 
oxide on the capacitor plates.

Also there can be a leaking resistance in insulators, e.g. by moisture.

All these losses together makes a parallel resistance (Rp) across the LC 
circuit.


Magnetic losses
This occurs when a magnetic material (iron) is placed near the coil.
Non magnetic materials (plastic, wood, aluminium etc.) don't give 
magnetic losses.

Why is the Q factor not constant for all frequencies?

The series resistance Rs gives a reduction of Q.
If we leave other losses out of consideration, the Q will have a value of:

Q= 2.pi.f.L / Rs

If the value of Rs is constant, the value of Q will increase with 
increasing frequency (f).
A series resistance in the circuit will especially give a reduction of Q 
at lower frequencies.

On the other hand:
if we only look at the losses caused by the parallel resistance Rp, the 
Q will have a value of:

Q=Rp / (2.pi.f.L)

Here we see, that at a constant value of Rp, the Q will decrease with 
increasing frequency (f).
A parallel resistance across the circuit will especially give a 
reduction of Q at higher frequencies.

The value of Q will both depend on series and parallel resistance, it is 
possible that a LC circuit gives a increasing Q at increasing frequency 
(because of series resistance) and than Q will reduce (because of the 
parallel resistance).
In this case we have a peak in Q somewhere in the frequency band.

Often the losses caused by the parallel resistance are the highest, and 
we only see a reduction of Q at higher frequencies in the medium wave band.
Than there is also a peak in Q, but this occurs at a frequency lower 
than we use.

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More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-28 13:42 -0500
  Re: More inductor talk, Proximity effect, self capacitance boB <boB@theresnoplacelikehome.com> - 2016-09-28 14:08 -0700
    Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-28 17:06 -0500
      Re: More inductor talk, Proximity effect, self capacitance "Tim Williams" <tiwill@seventransistorlabs.com> - 2016-09-28 23:50 -0500
        Re: More inductor talk, Proximity effect, self capacitance boB <boB@theresnoplacelikehome.com> - 2016-09-28 22:27 -0700
      Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-10-03 15:46 -0500
  Re: More inductor talk, Proximity effect, self capacitance Winfield Hill <hill@rowland.harvard.edu> - 2016-09-28 15:38 -0700
    Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-28 19:16 -0500
    Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-28 22:06 -0500
      Re: More inductor talk, Proximity effect, self capacitance Winfield Hill <hill@rowland.harvard.edu> - 2016-09-28 20:17 -0700
        Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-29 06:13 -0500
          Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-29 08:29 -0500
            Re: More inductor talk, Proximity effect, self capacitance Winfield Hill <hill@rowland.harvard.edu> - 2016-09-29 06:54 -0700
              Re: More inductor talk, Proximity effect, self capacitance boB <boB@theresnoplacelikehome.com> - 2016-09-29 11:57 -0700
                Re: More inductor talk, Proximity effect, self capacitance Winfield Hill <hill@rowland.harvard.edu> - 2016-09-29 12:29 -0700
  Re: More inductor talk, Proximity effect, self capacitance George Herold <gherold@teachspin.com> - 2016-09-29 06:55 -0700
    Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-29 10:59 -0500
      Re: More inductor talk, Proximity effect, self capacitance makolber@yahoo.com - 2016-09-29 09:15 -0700
        Re: More inductor talk, Proximity effect, self capacitance amdx <nojunk@knology.net> - 2016-09-29 13:16 -0500

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