[upper part deleted]
Hi Wim,
It seems if you use a counterpoise or
whatever you want to call an RF ground
plane on the 3rd floor, you will reduce
lossy current flow through the floor,
etc., and maybe reduce current flow
through other wiring.
But the effect of doing that is to
increase the efficiency with which the
resonator radiates. That will probably
decrease its Q through loading. But is
radiation what you're trying to achieve?
I would think that the last thing one
wants to do is efficiently radiate RF
energy into everything in the far-field
as well as the near-field! One can have
a resonant LC circuit without
significant radiation.
Does that make sense?
I concur with suggestions to use filters
on the AC wiring. And the Faraday cage
may provide benefits as well.
Chuck
NT3G
Hi Chuck,
As all (most) coilers want to get the sparks at the top of the coil
(and not at the bottom), you need an electrically quarter wave circuit
(or LC series circuit where the top capacity + coil capacity forms the
capacitor). Another option may be a center fed (dipole) structure.
The problem with these is that air-breakthrough is not that
symmetrical, so when the air on the left side breaks first, you get
strong asymmetry that may cause a breakthrough from center to primary
feeding coil.
The quarter wave monopole has low impedance (in particular when it is
a short one [3ft at 500 kHz). All quarter wave circuits (whether
shorted or not) require a ground or something to pull out the drive
current for the coil.
When you make it large enough (or even extend the wire mesh on the
walls), you provide a return path for the displacement current (and in
the end a return path for streamers).
With respect to radiation.
You are right, some energy will leave as radiation, but it will be a
very small fraction of the input power. As le/lambda = (about)
0.0017, the radiation efficiency will be very low (compare it with a
0.13m monopole antenna at 80m). Over an infinite ground plane the
radiation resistance will be about 1m Ohm. Assuming about 30 ohms of
AC resistance of the coil, the radiation efficiency will be 0.004%.
When someone adds a large top capacitor, the radiation resistance will
increase, but with factor 4 maximum.
As soon as air-breakdown occurs, all excess power will be converted
into heat. I think, the Q-factor is not limited by radiation losses,
but by conduction losses and at higher power levels Q-factor will
reduce due to air-breakdown. The same is valid for small loop
antenna's, Q is limited by heat losses, to much input power causes the
tuning capacitor to arc.
You can reduce the far field radiation (and near field to the adjacent
apartment) by bending the ground plane upwards (on the walls of the
apartment). When you extend it higher then the top of the coil, you
made a coaxial quarter wave resonator (with low near field and far
field radiation).
So in my opinion providing a defined "return path" for the bottom feed
current of the coil will result in maximum power in the ionized air.
When you also want to minimize near field and far field radiation, you
should construct a faraday cage (or similar structure with wires).
Best regards,
Wim
PA3DJS