Eric Dollard

[orgonaut314]

No that is not what it should look like. I give reasons why, you do not. The picture of the dipole shows 2 1/4 transversal wave antenna's. It shows I and E just like your 1/4.

My point is both are transversal. Eric's antenna is longitudional.

Read that again.

Eric's antenna is longitudional. It would be transversal if the capacity between the windings is very small. Perhaps you have to much space between the windings? I use litze. Very good because it also minimises the eddy currents in the wires. Perhaps you have build a normal antenna? I have used the capacity between the winfings that constitute a second current to the top. The sum of these currents act different than a long wire. There is not even a wave. The wave has reversed harmonics Eric calls it a wave in counter space.

It should not look like a normal stretched wire antenna unless the capacitive coupling between wires is very small.

I will not repeat this point more times as I did repeat it several times now with a ****load of reading material and simulations.

[dR-Green]

I keep posting the Marconi antenna because that's what the distribution should look like. It's a monopole antenna, 1/4 wave. Note the location of the ground plane and VIRTUAL "image antenna". Dipole is 1/2 wave.

[orgonaut314]

You keep posting that Marconi antenna. I can find other pictures of dipoles like this one.



Understanding Antenna Specifications and Operation | DigiKey

It is a simple transmission line. The Tesla coil is not a simple transmission line. It does not have the same resonance characteristics.

[dR-Green]

I am measuring what I expect to see and it is grounded with copper in the garden and the electric field is max on top. I see no point in distrusting the measurement as I repeated many times with different testcoils same result just as expected.

I will try to post the resonance spectrum in short. It is completely different from a normal transversal dipool antenna. the harmonics are to the left mainly. It behaves like the simulation of a longitudional network basically.

Oh and the lower internal resistance 6080 tube makes the pi network much easier to handle. It is not even needed anymore. Next step will be to put the 6sn7 in front of the 6080. My voltages still are very low but than I have to take more care of the environment.

Do you have details on the coil like design frequency, luminal frequency, conductor length, dimensions etc.

You say the current is max at the free end but have you measured the potential?

A dipole antenna is a 1/2 wave antenna, because it has two (split) poles with the oscillator in the middle. Standard 1/4 wave distribution should be like this, which is what I always see except in the case that it's not resonating in 1/4 wave

[orgonaut314]

I am measuring what I expect to see and it is grounded with copper in the garden and the electric field is max on top. I see no point in distrusting the measurement as I repeated many times with different testcoils same result just as expected.

I will try to post the resonance spectrum in short. It is completely different from a normal transversal dipool antenna. the harmonics are to the left mainly. It behaves like the simulation of a longitudional network basically.

Oh and the lower internal resistance 6080 tube makes the pi network much easier to handle. It is not even needed anymore. Next step will be to put the 6sn7 in front of the 6080. My voltages still are very low but than I have to take more care of the environment.

[dR-Green]

Hi Dr-Green:

Do you use Litz wire for your coils? If you do, what is the strand count and the gauge of each strand? In general, would the use of Litz wire for coils be beneficial do to the high frequencies at which these experiments are being run?

The 15% secondary is wound with 2x 22 SWG I think, but the only reason for that was to reduce the gap between each turn and I had plenty of 22 SWG at hand. Coils built since then have had the conductor diameter chosen on the basis of the spacing alone.

I think this came up before though, as well as using copper strip. So in that respect it's probably "better" because the copper inside the wire isn't doing anything. But this is why Eric recommends the coax.

[Nhopa]

Wire type

Hi Dr-Green:

Do you use Litz wire for your coils? If you do, what is the strand count and the gauge of each strand? In general, would the use of Litz wire for coils be beneficial do to the high frequencies at which these experiments are being run?

[dR-Green]

I think the middle reads max because we can not measure a single winding and in the middle the average distance to all windings is the least. But you do see clearly that on the top the field is stronger than it is on the bottom.

I do expect this too because this is not a normal transversal quarter wave resonance. The mutual inductance changes the whole behaviour of the wave.

I think the problem there is that the test equipment is much too close to the coil. As you approach the free end it becomes all the more sensitive, so when you are measuring the top it gives you a lower reading relative to the middle because it's detuned more so the output is actually less.

Keep the probe in the same place and put your hands near the coil and you will see what happens on the meter. The probe itself also has the same effect when you put it near the coil to do measurements. So the coil should be kept clear. Ideally you don't even want measurement probes in the field at all, but that's the only way to get measurements. So keep MAXIMUM distance between probes and coil at all times. Only have it so close as to make measurement possible. The actual values are meaningless so you don't have to try to get the highest numbers.

For measuring the current try a SINGLE loop of wire about 1/3 the diameter of the secondary coil, and for measuring voltage use a wire point or such small and pointy surfaces.

Also if the analogue meter and tube are still connected take them off. Is the secondary grounded? If it's just a ground plane (capacitance) and the capacitance on the top end is bigger then your 1/4 wave distribution will be upside down.

[orgonaut314]

Here I am measuring with a small coil on the lower end of the secondary. The middle of the small coil is on the lowest ring. The voltage reads 4,77V.



This one is on the middle of the secondary. The voltage reads 7,60V.



Here I am measuring on the top of the secondary. The middle of the small coil is on the highest ring. The voltage reads 7,29V.



I think the middle reads max because we can not measure a single winding and in the middle the average distance to all windings is the least. But you do see clearly that on the top the field is stronger than it is on the bottom.

I do expect this too because this is not a normal transversal quarter wave resonance. The mutual inductance changes the whole behaviour of the wave.

[dR-Green]

I used a 6080 tube in my coil in stead of the 6sn7. The internal resistance of that coil is much lower and with the pi network it is very small.

I still measure the magnetic field going up towards the top. The magnetic measuring loop horizontal.

I don't know, it should be the other way. Where is the highest potential measured? Obviously it can't be on the ground end if it's grounded.

How are you measuring the current distribution?

Also when possible the setup should be in the middle of the room or as far away from other objects as possible because they will affect it. Your audio amplifier is probably getting a nice bit of energy too!

[orgonaut314]

I used a 6080 tube in my coil in stead of the 6sn7. The internal resistance of that tube is much lower and with the pi network it is very small.

I still measure the magnetic field going up towards the top. The magnetic measuring loop horizontal.

[dR-Green]

I'll do the frequency sweep tests and the spectrum again using only the secondary in the next couple of days. I have 20% 20 turn secondary and 15% 17 turn secondary designed for the same frequency. I expect to see a standard 1/4 wave distribution with maximum voltage at the free end and maximum current on the ground end. The RF current probe I used before has been reconfigured/dismantled so this time I'll use a loop of wire and scope for that purpose, and may end up with some phase measurements too.

[orgonaut314]

Sorry I had to edit the last post because I suddenly understood it better.

[orgonaut314]

Hi drGreen, I will try to explain simpler for everyone to understand what I am thinking and if I make an error please say so.

To start lets look at a simple transmission line resonance. With two parallel wires we can think of the wire as a succession of capacitors and inductors. When the end of the two wires is left open (not connected) we have in fact a one wire transmission line or an antenna.

Normally in a circuit the wires are not seen as transmission lines because they carry dc or the frequencies are so low that there are no waves. But even than the wire is seen as a capacity and an inductance but the fact that these vallues are distributed does not matter than.

Now we are studying the antenna. That is a transmission line open ended. If the line is not wound in a coil we can use the following simple schematic for the line.



To see what is really happening this simulation has to be refined into infinite many nodes. That is difficult to do in software but on paper you can use capacitors with length dx and inductors with length dx. If you write down the relations for voltage and current in dx vallues you end up with a differential equation that gives a relation for voltage and current depending on time and space. A solution to that equation is a sine wave both for voltage and current. To find the real vallues the end conditions have to be matched and with voltage that means that at the end point the voltage can swing and the current must be zero.

In the simulation there are only 4 nodes and this seems to lead to maximum 4 harmonics witch means that there is a certain frequency that produces a standing wave with maximum voltage swing on the open end. Than there is a wave with another frequency that has 2 maxima and the next frequency has 3 maxima.

The voltage on the end note is plotted and we see that there is one ground frequency and three harmonics.




Now if we change the straight wire by winding it into a coil we change two thing. First the magnetic field in the windings now couples to the other windings and the electric field couples too. We now get this schematic



That has two currents going.
Horizontal


Vertical


This adds up to


All the vertical mutual inductance K and M are part of the longitudional current and all the self capacitance (to earth) and self inductance of the bare wire without the coil are part of the transversal current.

The resonance now looks different and it resembles a longitudional archetype network showed before.

Important to note is that the solution to the differential equation that results when we take capacitors and inductors of length dx is not a wave function. So the whole story about harmonics does not apply. Yet when we study this solution that the simulator shows us we see some wave like behavior. But different. There are no harmonics in the wave sense but Eric still calls these peaks to the left harmonics for some reason. We have to ask him.

[dR-Green]

This time 'waves' with lower frequencies are harmonics.

There are such things as "undertones" although acoustic instruments don't naturally tend to produce them.

The table doesn't show what happens at higher frequencies. Is there no resonant peak above the fundamental?

[edit] But again, harmonics in this context usually refer to harmonic frequencies produced by something oscillating, as in a harmonic spectrum of an oscillating string at a fixed frequency. Resonant peaks are different. Is this a harmonic spectrum, or a graph of the resonant peaks after doing a frequency sweep? I notice Eric refers to them as a "resonant series" in the diagram and not "harmonics", suggesting it's a series of resonant peaks found when doing a frequency sweep.