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RF ground in an apartment.

S

Steve

Jan 1, 1970
0
I live in an apartment, on the second floor. I am finally finishing
up a tesla coil, but I don't have an rf ground. Would placing a
ground plane of wire mesh work? How big should it be? Would say,
4x4ft suffice? The coil is appx 3ft tall, 7.5kV NST, 17.5in tall
secondary, really not too big.

Also, I want to build a faraday cage for the coil. It isn't
necessarily a large coil, but I don't want to cause any interference
for anyone. Is aluminum screen acceptable for a cage?

Also, I have a standard box power filter, mfg: corcom, model: 20VK6.
To keep rfi from entering back into the power line, do I hook the
filter up normally, with line going to line and load going to load, or
backward, with line to load and load to line?

Thanks for all help,
Steve
 
W

Wimpie

Jan 1, 1970
0
I live in an apartment, on the second floor. I am finally finishing
up a tesla coil, but I don't have an rf ground. Would placing a
ground plane of wire mesh work? How big should it be? Would say,
4x4ft suffice? The coil is appx 3ft tall, 7.5kV NST, 17.5in tall
secondary, really not too big.

Also, I want to build a faraday cage for the coil. It isn't
necessarily a large coil, but I don't want to cause any interference
for anyone. Is aluminum screen acceptable for a cage?

Also, I have a standard box power filter, mfg: corcom, model: 20VK6.
To keep rfi from entering back into the power line, do I hook the
filter up normally, with line going to line and load going to load, or
backward, with line to load and load to line?

Thanks for all help,
Steve

Hello Steve,

When you do it right, your Tesla coil resonates like a quarter wave
resonator. That one needs a ground (the same way as a mono pole
antenna needs a ground or counterpoise).

The second reason for a ground is to reduce RFI. Unless you make a
faraday cage, you cannot avoid RFI completely. I don't know whether
you are making a pulsed or CW Tesla Coil, but the power involved is
that high that some interference may occur.

You can enhance the effect of the ground (and reducing probability of
RFI) by adding many wires to your ground surface and spread them out
(radially) in your apartment (in fact you extend the ground with the
wires). You can even run them upwards (recommended). When you setup
the coil in a corner, you can use the walls to hold the vertical part
of the wires. In fact you make a faraday cage without a roof.

Regarding the filter, the enemy will be so called common mode noise.
The best thing is to place any filtering for signal and power lines at
that point where you have maximum metal or mesh surface (so the mesh
and radial wires are in between the coil and cabling). So all
decoupling will be done with respect to that point.

I would install the Telsa setup (coil with ground plane) of the
ground and decouple all cabling (power supply, control, etc) with
respect to the ground mesh. All cables (inclusive the safety ground)
run beneath the ground plane (with wire extension).

When it is not possible to build the Tesla coil off the ground, I
would extend the mesh to at least one side and let it go upwards (for
about 6 ft). The lower corner I would use as a reference for filtering
(AC decoupling capacitors), entrance of cables and safety ground
connection (PE wire).

To further reduce RFI I would provide large ferrite cores to all
cables (control, power, safety ground) that leave the Tesla coil setup
(do not put ferrites around the radial ground extension wires.

I hope this will help you a bit. When you feel something is not clear
(sorry, I have no image), you may contact me.

Best regards,

Wim
PA3DJS
 
S

Steve

Jan 1, 1970
0
Hello Steve,

When you do it right, your Tesla coil resonates like a quarter wave
resonator. That one needs a ground (the same way as a mono pole
antenna needs a ground or counterpoise).

The second reason for a ground is to reduce RFI. Unless you make a
faraday cage, you cannot avoid RFI completely. I don't know whether
you are making a pulsed or CW Tesla Coil, but the power involved is
that high that some interference may occur.

You can enhance the effect of the ground (and reducing probability of
RFI) by adding many wires to your ground surface and spread them out
(radially) in your apartment (in fact you extend the ground with the
wires). You can even run them upwards (recommended). When you setup
the coil in a corner, you can use the walls to hold the vertical part
of the wires. In fact you make a faraday cage without a roof.

Regarding the filter, the enemy will be so called common mode noise.
The best thing is to place any filtering for signal and power lines at
that point where you have maximum metal or mesh surface (so the mesh
and radial wires are in between the coil and cabling). So all
decoupling will be done with respect to that point.

I would install the Telsa setup (coil with ground plane) of the
ground and decouple all cabling (power supply, control, etc) with
respect to the ground mesh. All cables (inclusive the safety ground)
run beneath the ground plane (with wire extension).

When it is not possible to build the Tesla coil off the ground, I
would extend the mesh to at least one side and let it go upwards (for
about 6 ft). The lower corner I would use as a reference for filtering
(AC decoupling capacitors), entrance of cables and safety ground
connection (PE wire).

To further reduce RFI I would provide large ferrite cores to all
cables (control, power, safety ground) that leave the Tesla coil setup
(do not put ferrites around the radial ground extension wires.

I hope this will help you a bit. When you feel something is not clear
(sorry, I have no image), you may contact me.

Best regards,

Wim
PA3DJS

Sorry for not specifying the type of coil. It is a standard spark gap
coil, with the basic components: hv transformer, capacitor, spark gap,
primary, secondary, topload.

I think I understand what you mean. What size capacitors should I
use? Based on my calculations, it should oscillate somewhere in the
500kHz region. Just to make sure, decoupling capacitors go in series
with the circuit, correct)? I had planned on my control wire to just
be a switch between mains and the neon sign transformer.

Also, my transformer states the center tap is connected to transformer
case and ground stud. I have read to connect RF ground to the center
of the spark gap as well as the center tap of the transformer. Should
I do this, and just leave AC ground off the transformer, and will this
cause any shock danger, being that the RF ground isn't connected to
earth and could be floating?

Thanks for the help,
Steve
 
W

Wimpie

Jan 1, 1970
0
Sorry for not specifying the type of coil. It is a standard spark gap
coil, with the basic components: hv transformer, capacitor, spark gap,
primary, secondary, topload.

I think I understand what you mean. What size capacitors should I
use? Based on my calculations, it should oscillate somewhere in the
500kHz region. Just to make sure, decoupling capacitors go in series
with the circuit, correct)? I had planned on my control wire to just
be a switch between mains and the neon sign transformer.

Also, my transformer states the center tap is connected to transformer
case and ground stud. I have read to connect RF ground to the center
of the spark gap as well as the center tap of the transformer. Should
I do this, and just leave AC ground off the transformer, and will this
cause any shock danger, being that the RF ground isn't connected to
earth and could be floating?

Thanks for the help,
Steve

High Steve,

I sent a reply directly to you, I hope it did reach you, I had some
problems sending it.

Best regards,

Wim
PA3DJS
 
D

default

Jan 1, 1970
0
I live in an apartment, on the second floor. I am finally finishing
up a tesla coil, but I don't have an rf ground. Would placing a
ground plane of wire mesh work? How big should it be? Would say,
4x4ft suffice? The coil is appx 3ft tall, 7.5kV NST, 17.5in tall
secondary, really not too big.

Also, I want to build a faraday cage for the coil. It isn't
necessarily a large coil, but I don't want to cause any interference
for anyone. Is aluminum screen acceptable for a cage?

Also, I have a standard box power filter, mfg: corcom, model: 20VK6.
To keep rfi from entering back into the power line, do I hook the
filter up normally, with line going to line and load going to load, or
backward, with line to load and load to line?

Thanks for all help,
Steve

You really should have a good earth ground. Is that out of the
question? House wiring is more like an antenna then RF ground - it
snakes around forever before going to ground at the entry point power
panel (meter). I sunk a 10 foot copper pipe outside the wall where my
TC sat with a 5 foot heavy gauge wire to it.

Most TC's of the size you are talking about would work at a lower
frequency like 100 KHZ, but that is all a matter of how many turns of
wire etc.. - the faraday shield/cage would also increase the capacity
and lower the frequency.

Put in a safety gap at the input to the transformer. And a couple of
ferrite chokes with Teflon or HV insulation on the wire for the chokes
in each leg of the HV - assuming the NST is center tap grounded.

A safety gap prevents reflected RF from getting into the transformer
and back into the power lines. There will be SWR problems until the
coil is in tune . . . AND of course a good power line filter.

Consider liability - you aren't just talking about TVI, you could set
fire to the apartment, computers on the same power line or in close
proximity to the TC may die - my TC's could eat DRAM chips and reset
the CMOS settings on my computer 6 feet away from a 1 KVA TC.
(unplugging the computer AND modem AND all peripherals from the power
line would keep it safe) Other sensitive equipment in the vicinity may
be ruined (or not) my speakers took some direct hits to the wood cases
and the mosfet amp didn't suffer. You probably don't want neighbor's
with pacemakers around.

The pupman forum is an excellent source for all kinds of TC/HV
questions. It is operated as a mailing list - you can use your email
account and regular reader or use a web-based email account
(recommended). You have to join the list to post but can read
anything in the archives without joining.

You download the list mailing via a regular news reader or web based
email. Read some of the archives before posting so you have a feel
for how things are done.

http://www.pupman.com/ If these folks don't know it, no one does.
 
S

Steve

Jan 1, 1970
0
You really should have a good earth ground. Is that out of the
question? House wiring is more like an antenna then RF ground - it
snakes around forever before going to ground at the entry point power
panel (meter). I sunk a 10 foot copper pipe outside the wall where my
TC sat with a 5 foot heavy gauge wire to it.

Most TC's of the size you are talking about would work at a lower
frequency like 100 KHZ, but that is all a matter of how many turns of
wire etc.. - the faraday shield/cage would also increase the capacity
and lower the frequency.

Put in a safety gap at the input to the transformer. And a couple of
ferrite chokes with Teflon or HV insulation on the wire for the chokes
in each leg of the HV - assuming the NST is center tap grounded.

A safety gap prevents reflected RF from getting into the transformer
and back into the power lines. There will be SWR problems until the
coil is in tune . . . AND of course a good power line filter.

Consider liability - you aren't just talking about TVI, you could set
fire to the apartment, computers on the same power line or in close
proximity to the TC may die - my TC's could eat DRAM chips and reset
the CMOS settings on my computer 6 feet away from a 1 KVA TC.
(unplugging the computer AND modem AND all peripherals from the power
line would keep it safe) Other sensitive equipment in the vicinity may
be ruined (or not) my speakers took some direct hits to the wood cases
and the mosfet amp didn't suffer. You probably don't want neighbor's
with pacemakers around.

The pupman forum is an excellent source for all kinds of TC/HV
questions. It is operated as a mailing list - you can use your email
account and regular reader or use a web-based email account
(recommended). You have to join the list to post but can read
anything in the archives without joining.

You download the list mailing via a regular news reader or web based
email. Read some of the archives before posting so you have a feel
for how things are done.

http://www.pupman.com/ If these folks don't know it, no one does.

Thanks to everyone for the replies. I will have to look at the forum.

I can't put in a good earth gound because I'm on the third floor, and
the apt won't let me run any wires outside etc... so all I have is the
mains ground, which I'm sure is probably shared with a few units.

So, that's why I was trying to find out if just the Faraday cage and
ground plane would be sufficient. If it's iffy, and I could hurt
someone elses equipment, I'll just wait until I get a house. I'm not
out to make anyone elses life difficult.

Thanks,
Steve
 
C

Chris Jones

Jan 1, 1970
0
Steve said:
I live in an apartment, on the second floor. I am finally finishing
up a tesla coil, but I don't have an rf ground. Would placing a
ground plane of wire mesh work? How big should it be? Would say,
4x4ft suffice? The coil is appx 3ft tall, 7.5kV NST, 17.5in tall
secondary, really not too big.

Also, I want to build a faraday cage for the coil. It isn't
necessarily a large coil, but I don't want to cause any interference
for anyone. Is aluminum screen acceptable for a cage?

Also, I have a standard box power filter, mfg: corcom, model: 20VK6.
To keep rfi from entering back into the power line, do I hook the
filter up normally, with line going to line and load going to load, or
backward, with line to load and load to line?

Thanks for all help,
Steve

I would think about finding somewhere other than an apartment to run the
coil, as it is quite likely to upset the neighbours, and damage their
appliances etc. Do you know anyone who lives on a farm by any chance? If
not, the Faraday cage is a good start. If the coil is inside the cage, and
the ground of the coil is connected to the bottom of the cage, then the
thing you need to take care of is any wires that go in or out of the
Faraday cage. At the point where any wire goes through the cage, it needs
to be connected RF-wise to the cage. It doesn't matter whether the cage is
connected to the real ground two stories below, but the cage should be
connected to the ground of your power cable, and the live and neutral wires
should go into the cage by way of a filter, the ground casing of the filter
being connected directly to the cage. You will need a very good filter.
The most important thing about the Faraday cage is that any joins in the
mesh need to be really well connected, and all the way along, not just in
one place. It is unlikely that you can get a really good connection
between pieces of aluminium mesh if it is anodised or painted - you would
have to get that coating off and it would be difficult. If you can get
hold of some bare metal mesh then that would be ideal, maybe chicken wire
(galvanised iron wire with about half inch holes) might be OK if you could
solder the joins.

Chris
 
D

default

Jan 1, 1970
0
If you go for the faraday cage, try to find wire screen that is
hot-dipped after it is woven - like chicken fence or "hardware cloth."
Hot-dipping in zinc insures a connection at the joints between wires.

A clean wire brush in an electric drill will buff the zinc so it will
take solder - then you just need something like a large soldering iron
and some sheet metal to make mounting points for the cage filters.

A few of the pupman list subscribers are in the business of building
and displaying large TC's they build cages for them to use inside
shopping malls and museums with temporary facilities and probably no
earth grounds

Richard Hull (one list subscriber) had some of his coils shown in
National Geographic years ago (it may be July 93) the article was
about lightening and they sensationalized it but the pictures were
worth the price. Richard has moved on to "Farnsworth Fusers" but may
still put in a word from time to time. He was working in the class of
devices that used "pole pigs" (pole mounted distribution transformers)
reverse connected to produce the excitation sparks for his coils.
 
S

Steve

Jan 1, 1970
0
I would think about finding somewhere other than an apartment to run the
coil, as it is quite likely to upset the neighbours, and damage their
appliances etc. Do you know anyone who lives on a farm by any chance? If
not, the Faraday cage is a good start. If the coil is inside the cage, and
the ground of the coil is connected to the bottom of the cage, then the
thing you need to take care of is any wires that go in or out of the
Faraday cage. At the point where any wire goes through the cage, it needs
to be connected RF-wise to the cage. It doesn't matter whether the cage is
connected to the real ground two stories below, but the cage should be
connected to the ground of your power cable, and the live and neutral wires
should go into the cage by way of a filter, the ground casing of the filter
being connected directly to the cage. You will need a very good filter.
The most important thing about the Faraday cage is that any joins in the
mesh need to be really well connected, and all the way along, not just in
one place. It is unlikely that you can get a really good connection
between pieces of aluminium mesh if it is anodised or painted - you would
have to get that coating off and it would be difficult. If you can get
hold of some bare metal mesh then that would be ideal, maybe chicken wire
(galvanised iron wire with about half inch holes) might be OK if you could
solder the joins.

Chris

I think you're right. I may just wait until I have a house. I don't
want to risk damaging someone elses equipment, that wouldn't be very
responsible of me.

So, if the cage itself is connected to power ground, which in my case
is AC ground, as long as all wires going in and out are filtered
properly, there should not be any RF present on the ground wire?

Just to clarify, how do I properly decouple the wires going through
the cage? I'm used to seeing feedthrough capacitors in RF equipment,
something along this principle? I'm having some trouble figuring out
which ground is acceptable to connect where, but I will do my
research, and likely put this project on hold until I have a more
acceptable location.

Steve
 
H

Homer J Simpson

Jan 1, 1970
0
I think you're right. I may just wait until I have a house. I don't
want to risk damaging someone elses equipment, that wouldn't be very
responsible of me.

So, if the cage itself is connected to power ground, which in my case
is AC ground, as long as all wires going in and out are filtered
properly, there should not be any RF present on the ground wire?

Just to clarify, how do I properly decouple the wires going through
the cage? I'm used to seeing feedthrough capacitors in RF equipment,
something along this principle? I'm having some trouble figuring out
which ground is acceptable to connect where, but I will do my
research, and likely put this project on hold until I have a more
acceptable location.

Even a small unit like a Violet Ray may toast all of your electronics - and
your neighbors' as well. You need a rock solid filter for the AC line
alone - and good insurance.
 
D

default

Jan 1, 1970
0
So, if the cage itself is connected to power ground, which in my case
is AC ground, as long as all wires going in and out are filtered
properly, there should not be any RF present on the ground wire?
That makes sense.
Just to clarify, how do I properly decouple the wires going through
the cage? I'm used to seeing feedthrough capacitors in RF equipment,
something along this principle? I'm having some trouble figuring out
which ground is acceptable to connect where, but I will do my
research, and likely put this project on hold until I have a more
acceptable location.

Yes feed through filters are good for this - cap and inductors in one
device. The NEC power cord filters one sees on computers and such may
work well. Switching power supplies are up in the TC coil range these
days, so those types of filters may work.

A device used in auto radios of old (50's) was something called a
"spark plate" (had nothing to do with sparks). It was a piece of mica
(high dielectric constant, low loss) on the outside of the chassis
often with a rivet or bolt carrying the battery connection to the
outside world, and a square piece of copper. Only a few pico farads
but very effective for high frequency noise. The chassis formed one
side of the capacitor and the copper the other (somewhat harder to
make safe with mains voltage).

I assume it got the name "spark plate" from auto mechanics that
accidentally grounded the hot copper piece exposed on the outside of
the chassis.

I've used that idea to decouple gunn diodes used in radar jammers.
Solder a nut to the thin pcb material and it decouples the power and
provides an isolated mount for the diode. (gunn diodes won't
oscillate if the voltage lead has inductance).
 
S

Steve

Jan 1, 1970
0
That makes sense.


Yes feed through filters are good for this - cap and inductors in one
device. The NEC power cord filters one sees on computers and such may
work well. Switching power supplies are up in the TC coil range these
days, so those types of filters may work.

A device used in auto radios of old (50's) was something called a
"spark plate" (had nothing to do with sparks). It was a piece of mica
(high dielectric constant, low loss) on the outside of the chassis
often with a rivet or bolt carrying the battery connection to the
outside world, and a square piece of copper. Only a few pico farads
but very effective for high frequency noise. The chassis formed one
side of the capacitor and the copper the other (somewhat harder to
make safe with mains voltage).

I assume it got the name "spark plate" from auto mechanics that
accidentally grounded the hot copper piece exposed on the outside of
the chassis.

I've used that idea to decouple gunn diodes used in radar jammers.
Solder a nut to the thin pcb material and it decouples the power and
provides an isolated mount for the diode. (gunn diodes won't
oscillate if the voltage lead has inductance).

Interesting, I"ve never even heard of them.

So, if I decide to change gears completely, lose the Faraday cage and
ground plane altogether and put in a proper RF ground, I assume the
same filtering still applies to the mains wiring to keep RF out of the
115V supply, it just won't be connected to a cage? I will probably
put this project on hold until I have the proper facilities, at which
point I'll do the proper research and figure out how to do it right.

Thanks to everyone for their help, I think this will wait until a
later day.

Steve
 
W

Wimpie

Jan 1, 1970
0
[main part deleted]
Interesting, I"ve never even heard of them.

So, if I decide to change gears completely, lose the Faraday cage and
ground plane altogether and put in a proper RF ground, I assume the
same filtering still applies to the mains wiring to keep RF out of the
115V supply, it just won't be connected to a cage? I will probably
put this project on hold until I have the proper facilities, at which
point I'll do the proper research and figure out how to do it right.

Thanks to everyone for their help, I think this will wait until a
later day.

Steve

Hi Steve,

You need an RF-ground, because you are using a quarter wave resonator.
When you don't make a construction that serves as RF-ground, all
return current will flow through the power cable (so the power cable
and everything connected to it serves as RF-ground). This is
undesirable.

The reason for the faraday cage or large ground plane is to force the
E-field lines into your artificially created ground, so the induced
current can return to the base of the coil via a known safe path. In
other words the cage or ground plane is the RF-ground. For safety
reasons you connect your RF-ground to PE. When you did de construction
correctly, there will be little RF current in the wire that is between
RF-ground and PE.

Off course, when you have a large terrain available, you can use
mother earth as an RF-ground (in same way as medium wave broadcast
transmitters). www.pupman.com is good site to start with.

BTW, did my mail arrive?

Best regards,

Wim
PA3DJS
 
S

Steve

Jan 1, 1970
0
[main part deleted]
Interesting, I"ve never even heard of them.

So, if I decide to change gears completely, lose the Faraday cage and
ground plane altogether and put in a proper RF ground, I assume the
same filtering still applies to the mains wiring to keep RF out of the
115V supply, it just won't be connected to a cage? I will probably
put this project on hold until I have the proper facilities, at which
point I'll do the proper research and figure out how to do it right.

Thanks to everyone for their help, I think this will wait until a
later day.

Steve

Hi Steve,

You need an RF-ground, because you are using a quarter wave resonator.
When you don't make a construction that serves as RF-ground, all
return current will flow through the power cable (so the power cable
and everything connected to it serves as RF-ground). This is
undesirable.

The reason for the faraday cage or large ground plane is to force the
E-field lines into your artificially created ground, so the induced
current can return to the base of the coil via a known safe path. In
other words the cage or ground plane is the RF-ground. For safety
reasons you connect your RF-ground to PE. When you did de construction
correctly, there will be little RF current in the wire that is between
RF-ground and PE.

Off course, when you have a large terrain available, you can use
mother earth as an RF-ground (in same way as medium wave broadcast
transmitters). www.pupman.com is good site to start with.

BTW, did my mail arrive?

Best regards,

Wim
PA3DJS
Yes, I received your mail. Thanks for the picture, it was very clear.
I tried sending you a reply using two different email accounts, both
undeliverable. Thanks for all your help,
Steve
 
C

Chris Jones

Jan 1, 1970
0
Steve said:
Interesting, I"ve never even heard of them.

So, if I decide to change gears completely, lose the Faraday cage and
ground plane altogether and put in a proper RF ground, I assume the
same filtering still applies to the mains wiring to keep RF out of the
115V supply, it just won't be connected to a cage? I will probably
put this project on hold until I have the proper facilities, at which
point I'll do the proper research and figure out how to do it right.

Thanks to everyone for their help, I think this will wait until a
later day.

Steve

You would still need the cage with any scheme where the coil is operated in
your apartment, both for radiated interference and to stop an arc from just
directly hitting your light fittings or wires in you walls - that would
cause some conducted interference!

Chris
 
S

Steve

Jan 1, 1970
0
You would still need the cage with any scheme where the coil is operated in
your apartment, both for radiated interference and to stop an arc from just
directly hitting your light fittings or wires in you walls - that would
cause some conducted interference!

Chris

Good point. Just to clarify, by proper facilities, I meant moving
into a house where it's just my wife and I, but I may still do the
cage so I have no worries. I am a paranoid person by nature.

Steve
 
H

Homer J Simpson

Jan 1, 1970
0
Good point. Just to clarify, by proper facilities, I meant moving
into a house where it's just my wife and I, but I may still do the
cage so I have no worries. I am a paranoid person by nature.

Also use a damn good filter on the AC lines - like an IsoBar.
 
D

default

Jan 1, 1970
0
I am a paranoid person by nature.

Good, you'll live longer. Not paranoid - safe.

"there is no jesting with sharp edged tools"

Your main danger is the primary circuit - it is easy to mistake a gap
that has stopped firing for one that is turned off, check, double
check, and put the plug in your pocket while making adjustments with
one hand only. I good bright rotating beacon wouldn't be a bad idea.

Folks that use distribution transformers will add a time delay and
horn sounding before the mains voltage can be connected. Switches
have be operated from a safe distance, and in sequence.

Make sure others don't try to work the equipment when you aren't
there.

Make sure the tank cap has a way to discharge and know how long it
takes to reach a safe voltage. (normally only a second or two by
discharging through the NST) - but all it takes is a loose connection
to keep it charged, so use a shorting bar when you get ready to get
both hands in it.

Use ventilation - these things produce ozone like you won't believe.
Situate it so that an open window can exhaust the ozone.

Put a lock on it if you have children, or children will be present.

Warning signs aren't a bad idea
 
C

Chuck

Jan 1, 1970
0
Wimpie said:
[main part deleted]
Interesting, I"ve never even heard of them.

So, if I decide to change gears completely, lose the Faraday cage and
ground plane altogether and put in a proper RF ground, I assume the
same filtering still applies to the mains wiring to keep RF out of the
115V supply, it just won't be connected to a cage? I will probably
put this project on hold until I have the proper facilities, at which
point I'll do the proper research and figure out how to do it right.

Thanks to everyone for their help, I think this will wait until a
later day.

Steve

Hi Steve,

You need an RF-ground, because you are using a quarter wave resonator.
When you don't make a construction that serves as RF-ground, all
return current will flow through the power cable (so the power cable
and everything connected to it serves as RF-ground). This is
undesirable.

The reason for the faraday cage or large ground plane is to force the
E-field lines into your artificially created ground, so the induced
current can return to the base of the coil via a known safe path. In
other words the cage or ground plane is the RF-ground. For safety
reasons you connect your RF-ground to PE. When you did de construction
correctly, there will be little RF current in the wire that is between
RF-ground and PE.

Off course, when you have a large terrain available, you can use
mother earth as an RF-ground (in same way as medium wave broadcast
transmitters). www.pupman.com is good site to start with.

BTW, did my mail arrive?

Best regards,

Wim
PA3DJS

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
 
W

Wimpie

Jan 1, 1970
0
[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
 
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