Freq Splitting|Tesla-Coil.com

Date: Mon, 13 Feb 2006 23:35:56 -0700 - Subject: Frequency Splitting (Was: Tc first start)

Original poster: "C. Sibley"

Dr. Res,

What is frequency splitting as you mentioned below? New term to me...

Curt.

> Original poster: "D.C. Cox" >
>
> Most coils only produce short sparks on fire-up. Don't get discouraged! This is normal!!
>
> Using a small wire taped to your toroid you can check the distance to a ground stand to see the max spark distance.
>
> Next, the tuning process begins. You should always start with a "scrap wire" primary of 20-25 turns so you can investigate a wide range of primary inductance to bring your system into resonance. Start at 3 turns out and keep moving the tap out as you check each turn for "best resonance point".
>
> While doing tuning, keep your total sparkgap tight, usually around 0.100 inches. This will prevent high outputs which could damage your secondary coil if it's out of resonance with the primary coil.
>
> Also, be sure to never exceed 30-35% on your variac setting. Again, keep this low until you get your primary in resonance with your secondary. The best resonance point at these tight sparkgap and variac settings may only produce a spark 3-5 inches long. This is normal.
>
> After finding the proper primary number of turns for resonance, now you can open up the sparkgap total setting to 0.180 or 0.200 inches max setting. Then you can run the variac up to a higher level, ie, up to 100% and keep moving your groundstand back to see the longest striking distance.
>
> After the above tuning procedures you will be hitting longer sparks, and at this point you can replace the scrap wire primary with a #6 bare copper wire primary (like Home Depot #6 AWG ground wire) held in place with plastic holders.
>
> If your coil has a sec. coil of more than 4 inches dia. then a flat spiral primary is always the best setup. Using angle primaries can produce overcoupling and frequency splitting which leads to serious problems causing sec coil damage.
>
> Set up your scrap wire primary and let us know how it's working. also, specs on what you have would be helpful.
>
> Dr. Resonance >

Date: Tue, 14 Feb 2006 11:36:52 -0700 - Subject: Re: Frequency Splitting (Was: Tc first start)

Original poster: "D.C. Cox"

After coeff. of coupling increases past it's "critical value" the single resonant frequency of the secondary begins to split apart into two separate frequencies. This means the HV is not achieved at the very top of the coil but at some point lower in the sec windings which causes flashovers and racing sparks. As an example, a typical 4 inch dia. sec coil should be elevated above the primary coil (flat spiral) by 2 inches. Larger coils require even more elevation for best performance. You can experiment by using small blocks of wood to elevate your sec coil in 1/2 inch increments until best output spark is achieved. Using Bob Svangren's (ref TCBA Newsletters) segmented HV sparkgap provides excellent measurement of these small increases that might not be noticeable to the human eye.

An excellent description of this is in the ARRL Radio Amateur's Handbook available in any local library. Study this in detail.

Dr. Resonance

Date: Tue, 14 Feb 2006 16:10:02 -0700 - Subject: Re: Frequency Splitting (Was: Tc first start)

"After coeff. of coupling increases past it's "critical value" the single resonant frequency of the secondary begins to split apart into two separate frequencies. "

Is this only when spark gap is conducting? Is it not true that when the gap is quenched, the secondary will resonate at its natural frequency?

Tim

Date: Tue, 14 Feb 2006 17:45:02 -0700 - Subject: Re: Frequency Splitting (Was: Tc first start)

Original poster: "D.C. Cox"

Yes, but pri-sec reflections can produce bad effects during this period. This can produce irregular resonant peak potential points up and down the sec coil which can lead to damage.

The ARRL Radio Amateur's Handbook will detail these effects. See your local library.

Dr. Resonance

Date: Sat, 18 Feb 2006 10:04:15 -0700 - Subject: Re: Frequency Splitting (Was: Tc first start)

Original poster: "Antonio Carlos M. de Queiroz"
Tesla list wrote:

>Original poster: "D.C. Cox"
>After coeff. of coupling increases past it's "critical value" the
>single resonant frequency of the secondary begins to split apart
>into two separate frequencies. This means the HV is not achieved at
>the very top of the coil but at some point lower in the sec windings
>which causes flashovers and racing sparks. As an example, a typical
>4 inch dia. sec coil should be elevated above the primary coil (flat
>spiral) by 2 inches. Larger coils require even more elevation for
>best performance.
>You can experiment by using small blocks of wood to elevate your sec
>coil in 1/2 inch increments until best output spark is
>achieved. Using Bob Svangren's (ref TCBA Newsletters) segmented HV
>sparkgap provides excellent measurement of these small increases
>that might not be noticeable to the human eye.
>An excellent description of this is in the ARRL Radio Amateur's
>Handbook available in any local library. Study this in detail.

I'm sorry, but this is incorrect. Any reasonable Tesla coil operates deep into the region where two very distinct resonances can be observed. Actually, there are always two different resonances when two resonant tanks are coupled in any way. What happens is that if the losses are really big the two peaks merge in a single peak, if you try to find them with a frequency sweep. The two resonances are what causes the beats during the energy transfer. The splitting is due to the presence of the two coupled systems, primary and secondary, and has no relation with the other resonances of the secondary coil.

Antonio Carlos M. de Queiroz

Date: Sat, 25 Feb 2006 12:34:13 -0700 - Subject: Re: Frequency Splitting (Was: Tc first start)

Original poster: "Dmitry (father dest)"

Hallo Antonio,

Saturday, February 18, 2006, 11:04:15 PM, you wrote:

> Original poster: "Antonio Carlos M. de Queiroz"
> Tesla list wrote:

>>Original poster: "D.C. Cox"
>>
>>After coeff. of coupling increases past it's "critical value" the
>>single resonant frequency of the secondary begins to split apart
>>into two separate frequencies. This means the HV is not achieved at
>>the very top of the coil but at some point lower in the sec windings
>>

> I'm sorry, but this is incorrect. Any reasonable Tesla coil operates deep into the region where two very distinct resonances can be observed.

can i save some of my time (for studying sync motors : D) and get the answer from you, instead of finding it by myself? please : ) besides, i`m not only one who read this list, sooo - : )

the question is - the primary circuit alters Fres of secondary while sg fires, so secondary still resonates at it`s natural Fres (_other_ Fres)? then "This means the HV is not achieved at the very top of the coil but at some point lower in the sec windings" is incorrect too?
-----
Let the bass kick! =:-D

Original poster: Jared E Dwarshuis

I cringe when I see the words "frequency splitting", and I will tell you why. We could take two identical tank circuits and couple them. We will still get a beat frequency. Ah , but what about "frequency splitting?"

Be realistic, they are identical tank circuits. One tank could not possibly operate at a different frequency then the other. There is no "splitting".

However both tank circuits will now operate at a frequency that is different from the uncoupled state.

" There Is always a word or a phrase to be substituted for when meaning is lacking" (Imanuel Kant, paraphrased, and translated)

Sincerely: Jared Dwarshuis

Original poster: Ed Phillips

I cringe when I see the words "frequency splitting", and I will tell you why.

We could take two identical tank circuits and couple them. We will still get a beat frequency.

Ah , but what about "frequency splitting?"

Be realistic, they are identical tank circuits. One tank could not possibly operate at a different frequency then the other. There is no "splitting"."

With two identically-tuned circuits, before the spark gap quenches there will certainly be two frequencies present, with separation determined by the degree of coupling. Is that "frequency splitting"? All a matter of definition I guess. Of course, when the gap opens the secondary will ring with the fundamental resonant frequency.

Ed

Original poster: FIFTYGUY

In a message dated 5/23/06 5:13:15 PM Eastern Daylight Time,

>We could take two identical tank circuits and couple them. We will still get a beat frequency.
>
>Ah , but what about "frequency splitting?"
>
>Be realistic, they are identical tank circuits. One tank could not possibly operate at a different frequency then the other. There is no "splitting".
Doesn't a "beat frequency" result from two signals of different frequency? If so, what is the source of the other frequency? If not, how else does a "beat" result?

>However both tank circuits will now operate at a frequency that is different from the uncoupled state.

Are you saying the above observed "beat frequency" is the difference between the common "coupled frequency" and the common "uncoupled frequency"?

-Phil LaBudde

Original poster: "Daniel McCauley"
When two resonant circuits are coupled together, the frequency response contains two distinct peaks at two different frequencies. This is a result of each circuit seeing "more" of the capacitance of the other's circuit when they are coupled together. So, the fres of one goes up, and the fres of one goes down, and this is what you see when you perform an AC response of the coupled resonant circuits.

The beat frequency is the upper pole - the lower pole. The beat frequency is also the frequency at which primary notching occurs. Richie Burnett has some good theory on this subject on his website.

Dan

Date: Tue, 23 May 2006 19:20:16 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: <a1accounting

Hi Ed, >
>
> I cringe when I see the words "frequency splitting", and I will tell you why.
>
> We could take two identical tank circuits and couple them. We will
> still get a beat frequency.
>
> Ah , but what about "frequency splitting?"
>
> Be realistic, they are identical tank circuits. One tank could not
> possibly operate at a different frequency then the other. There is no "splitting"."

If the identical tank circuits are coupled, you are correct one tank does not operate at a different frequency (single). What happens is the original resonance in both tanks are replaced by two new resonances at either side of the original frequency ie the original frequency is split in to two frequencies. Both the secondary and primary have these two new resonances.
>
> With two identically-tuned circuits, before the spark gap
> quenches there will certainly be two frequencies present, with
> separation determined by the degree of coupling. Is that "frequency splitting"?
> All a matter of definition I guess. Of course, when the gap opens
> the secondary will ring with the fundamental resonant frequency.
>
> Ed

Original poster: Ed Phillips

>However both tank circuits will now operate at a frequency that is different from the uncoupled state.

Are you saying the above observed "beat frequency" is the difference between the common "coupled frequency" and the common "uncoupled frequency"?

-Phil LaBudde "

No - the "beat frequency" is the sum of the two COUPLED MODE frequencies, which shows maxima and minima a a rate corresponding to the difference between the two frequencies. Reall two different sine waves added together which appear to beat. Ed

Original poster: "Daniel McCauley"
Sorry Jared, that is incorrect on both accounts. If you had two identical tank circuits and coupled them together, there would be no beat frequency. Of course in the real world with tolerances on components, you would get a very small one, but in the ideal case, there would not be a beat frequency or frequency splitting as the amount of C each side sees would be identical.

Also, even with frequency splitting, the tank circuit doesn't operate a one single frequency. It operates with components of both major splitting frequencies (lack of a better word to call them) as well as additional harmonics which are very small compared to these two major frequency modes. Dan

Date: Tue, 23 May 2006 20:25:16 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: "Dr. Resonance"
The resonance points occur at two different frequencies each equidistant from the resonant peak. Maybe frequency splitting isn't the best term but two separate resonant freqs occur with overcoupling which produces two separate points along the coil when potential peaks occur. Then, these two pure freqs start "beating" against each other and standing waves occur.

Dr. Resonance

Date: Tue, 23 May 2006 21:41:25 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: "Daniel McCauley"

The resonant points, as you state, are not equidistance from the resonant peak. Each one is different, and can be defined by the following equations:

Fupper = Funcoupled / sqrt (1-k)

Flower = Funcoupled / sqrt (1+k)

where k = coupling between the two resonant circuits

Dan

>The resonance points occur at two different frequencies each
>equidistant from the resonant peak. Maybe frequency splitting isn't
>the best term but two separate resonant freqs occur with
>overcoupling which produces two separate points along the coil when
>potential peaks occur. Then, these two pure freqs start "beating"
>against each other and standing waves occur. Dr. Resonance

Date: Wed, 24 May 2006 10:27:11 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: "Dr. Resonance"

When we scope our coils and set the coeff of coupling the freqs move off of center evenly in both directions. I suppose it is possible to get one different from the other but in all cases I have seen involving TC tuning they always move to both left and right an even amount of space on the scope indicating equal off freq from center freq resonance points. When we adjust coeff of coupling with our drive motor I have never seen one point move more than the opposite freq point. This is, of course, without HVpower using only a sig gen as driving source.

Dr. Resonance

Original poster: Paul Nicholson

Hi All,

Many varied interpretations being presented here...

Dan wrote:
> If you had two identical tank circuits and coupled them together, there would be no beat frequency.

That bit's wrong. Perfect symmetry is no problem: the dual resonance behaviour is just fine when both LC units are identical. This is a common misunderstanding,

> the fres of one goes up, and the fres of one goes down,

That's the source of the error. It's incorrect to assign one frequency to one coil and the other frequency to the other coil. The important thing is that both of these modes involve a joint resonance of both coils. Hence there's no need for the symmetry breaking requirement which Dan suggested above.

Having said that, if one coil has its uncoupled Fres different to the other, there will be a difference in amplitudes of the two modes in each coil. The low frequency coil will have a higher proportion of V,I in the lower mode, and vice versa. The result under these conditions is incomplete instantaneous amplitude cancellation at the notches, resulting in incomplete energy transfer and difficult or impossible quenching - the system is 'out of tune'.

> When two resonant circuits are coupled together, the frequency response contains two distinct peaks at two different
> frequencies.

Two different frequencies, yes, but only distinct on a 'sweep' if k is greater than about 1/Q.

D.C. wrote:
> Maybe frequency splitting isn't the best term

There are some grounds for arguing that. In bringing up another resonator to the first, a second 'degree of freedom' is being introduced. It only appears as a 'splitting' of the previous single mode when the new resonator has its uncoupled Fres close to that of the first. It sure looks like a splitting when you watch the sweep as the coupling is increased, but it doesn't look at all like a splitting if you start with overcoupled k but with one coil tuned to a very low Fres. As you raise the Fres of that coil towards the other, the sweep will show the lower resonance peak appearing to 'push' the other resonance away.

> two separate resonant freqs occur with overcoupling which produces two separate points along the coil when potential
> peaks occur.

That's not quite right. For both modes, the potential peaks are at the secondary top.

> these two pure freqs start "beating" against each other and standing waves occur.

Seen in the time domain, they beat together to produce the desired beat envelope and notches.

But...standing waves always occur, regardless of k, so long as Q is greater than about 6. We *want* the standing waves - they are just another name for a resonance or 'mode'. It's incorrect to suggest that standing waves only occur during overcoupling and are undesirable.

(Of course, standing waves - resonances - higher than the two which make up the beat *are* likely to be undesirable because they do create additional voltage maxima within the secondary.)

Paul Nicholson - Manchester, UK.

Date: Wed, 24 May 2006 10:30:32 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: <a1accounting

Hi,
> Original poster: "Daniel McCauley" <dhmccauley@easternvoltageresearch.com>
>
> The resonant points, as you state, are not equidistance from the
> resonant peak. Each one is different, and can be defined by
> the following equations:
>
> Fupper = Funcoupled / sqrt (1-k)
>
> Flower = Funcoupled / sqrt (1+k)
>
> where k = coupling between the two resonant circuits
>
Actualy only true for simple (lumped) resonators. A more accurate version for our case would be

Fupper = Funcoupled / sqrt (1-k -(k^3)/6..)

Flower = Funcoupled / sqrt (1+k+(k^3)/6..)

which is an educated guess just to be provocative
snip

Date: Wed, 24 May 2006 10:32:44 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: <a1accounting

Hi, >
>
> Original poster: "Dr. Resonance" >
>
> The resonance points occur at two different frequencies each
> equidistant from the resonant peak. Maybe frequency splitting isn't
> the best term but two separate resonant freqs occur with overcoupling
> which produces two separate points along the coil when potential
> peaks occur. Then, these two pure freqs start "beating" against each
> other and standing waves occur.
>
The each of the two resonances frequencies in the secondary are caused by the standing waves. You could call them standing wave resonances or wave resonances.

The wave is reflected at the top end and reflected at the bottom end. At the bottom end the reflected impedance of the primary allows two possible resonances.

One way to look at the wave resonance is to say that the reflected waves from both the top and bottom are such that they beat and reinforce each other.

>From the perspective of the primary the two resonances (lumped) are
caused by the referred impedance of the secondary which is, due to the wave resonance, can be L or C either side of its normal wave resonance.

Date: Wed, 24 May 2006 12:07:52 -0600 - Subject: Re: Re: Frequency Splitting

Original poster: <a1accounting
Hi Dr,
>
> Original poster: "Dr. Resonance"

> When we scope our coils and set the coeff of coupling the freqs move
> off of center evenly in both directions. I suppose it is possible to
> get one different from the other but in all cases I have seen
> involving TC tuning they always move to both left and right an even
> amount of space on the scope indicating equal off freq from center
> freq resonance points.

Yes your correct. For K up to about 0.2 thats what you would see given by the following aproximation

Fupper = Funcoupled / (1-k/2)
Flower = Funcoupled / (1+k/2)

>When we adjust coeff of coupling with our
> drive motor I have never seen one point move more than the opposite
> freq point. This is, of course, without HVpower using only a sig gen
> as driving source.
>
> Dr. Resonance

Date: Wed, 24 May 2006 22:37:32 -0600 - Subject: Re: Frequency splitting...... Food For Thought

Original poster: Jared E Dwarshuis

We can actually use a mechanical model of a tuned coupled oscillator to gain insight into the nature of the phenomena of "Frequency Splitting"

We can have a spring stuck to a wall with a spring constant k and a mass m . Then we add a coupling spring (k prime) then an identical mass followed by another duplicate spring k (which we attach to the adjacent wall).

Now we need a relevant starting point. Let us hold the left mass stationary at its natural resting point where displacement equals zero.

Let us now displace the right mass an arbitrary unit of 1 to the right of its natural resting point.

Now let us examine the predicted frequency of the left mass at the instant where time equals zero. It is simply: w = sqrt (k/m). But what is the instantaneous frequency at time equals zero of the right side's mass that is displaced one unit. It is: w = sqrt(( k plus Kprime)/m)

Now the interesting part, is that given a duration of time we will find that the mass on the left has been displaced by -1 unit, and the mass on the right will have zero displacement. Thus at this instant in time, they have switched frequencies, where the right side now has the left sides old frequency, and the left side now has the right sides old frequency.

Implication: The frequency for a given side is constantly changing between sqrt (k/m) and the sqrt of ( k plus k prime)/ m.

Sincerely: Jared Dwarshuis