Re: Distributed capacitance effects Q?


"Richard Clark" <kb7qhc@xxxxxxxxxxx> wrote in message
news:4dt933db1qdt8e8pqtm24ihqrkorgoqc6h@xxxxxxxxxx
On Sun, 29 Apr 2007 14:30:29 -0500, "amdx" <amdx@xxxxxxxxxxx> wrote:

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Hi Mike,

This is then a characteristic of the Capacitor called D (dissipation).
Any increase in current tied to loss immediately goes to the bottom
line of resistance - it is a square law relationship, after all.

So your saying yes, the thought experiment would show more loss,
but the loss is in the capacitor. The loss in a capacitor would be
dielectric
and loss in the plates right?


Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)

Why not? Small loops suffer by comparison, and multi-turn loops even
more so.

I figure it would only confuse the issue.
I was trying to stay away from radiation resistance because my experience of
the effect Bill ask about has been with small aircore inductors. But on
second thought
even those have Rr.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

For wire separations beyond 3 or 4 wire diameters, the increase in
skin effect is small. It might be noted that interwinding Capacitance
also falls.

Why is it that when you get near self resonance of a coil the Q gets
lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to
tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)



Again, the answer must reside in Resistance. There are many
characteristics (wavelength, solenoid diameter, length, pitch, wire
gauge, self-capacitance, distributed capacitance, balance,
connections, earth proximity, radiation resistance) being juggled with
small Loop antennas and some (even many) choices that can be made to
resonate the antenna do not lead to an efficient solution.

Richard, I don't think anyone would disagree that the losses are resistive.
You seem to have answered the question I posted by saying it's increased
resistance.
Yes I agree,
Why does the reistance go up near resonance?

Mike


.

Relevant Pages

  • Re: RSGB RadCom December 2007 Issue
    ... The simple fact is that a ground screen reduces ground loss. ... Remove the screen and you have a lossy capacitor. ... expressed in terms of a ratio we commonly ... Ohms, in other regions as high as 1200 Ohms. ...
    (rec.radio.amateur.antenna)
  • Re: superconducting LC tank circuit?
    ... of the inductor and capacitor. ... it is still a LC tank circuit. ... Through heating of the wire. ... loss will be due to resistive loss in the materials and I^R heating. ...
    (sci.physics)
  • Re: Distributed capacitance effects Q?
    ... series with a small ideal resistor to represent its loss, ... Now shunt that combination coil+resistor with a small lossless ... capacitor, and note that the current in the capacitor will be small in ... resistance, & shunt capacitance draws less current and at slightly ...
    (rec.radio.amateur.antenna)
  • Re: Distributed capacitance effects Q?
    ... Any increase in current tied to loss immediately goes to the bottom ... line of resistance - it is a square law relationship, ... but the loss is in the capacitor. ... and loss in the plates right? ...
    (rec.radio.amateur.antenna)
  • Re: Distributed capacitance effects Q?
    ... capacitor of 300pF, but apparently that's not the case. ... entire coil as is the 200pF external capacitor. ... the self-resonant frequency, the lumped circuit model ... need to use the distributed network model (or Maxwell's ...
    (rec.radio.amateur.antenna)