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JavaTC vs. Sig gen and Scope

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Chris Maness

Mon Jul 06 2015, 06:12AM

Registered Member #55389 Joined: Mon Jul 06 2015, 12:38AM
Location: Grand Terrace, CA
Posts: 29

I used a sig gen and a scope to find the resonant frequency of a coil wound with #26 2.36" OD PVC 15.5" long with about 800 turns. I used various programs I found on the net to tell me the theoretical resonance of the secondary. This value was somewhere between 670kHz and 850kHz depending on what program. My measured value was 180kHz. I got the biggest peak at that frequency -- 2V in and 35V out. All of the other peaks at various little places that responded were much lower, and not as clean looking as that big sine wave at 180kHz. I am not sure which to believe. I have the primary, secondary, and furniture built. I am trying to figure out my cap based on a 12 Turn pancake of bare #10 copper across my top board that is 11.5". The fact that I have 10000V OBIT @23mA leads the program to suggest 6nF for my tank cap. I would need close to 30nF to achieve 180kHz. That seems to be on the large side.

I am not sure what to believe, as it seems the self resonance of crystal radio coils seem to be even lower for much smaller coils (these are CR's that don't have tank caps). This is why I am not quite ready to trust the program.

Any suggestions? I guess I can just whip up some salt water laden jars to test real quick, and if I get some nice streamers go for something more efficient.

Thanks,
Chris

Dr. Slack

Mon Jul 06 2015, 07:44AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The difference between 180kHz and 700kHz is beyond 'a bit of inaccuracy', and sounds more like a configuration problem. We can't guess what you're doing on this amount of data. I notice that the ratio is in the ballpark of sqrt(10), which is what you'd get with a misplaced decimal point.

Please post a circuit diagram of what you are measuring, the raw measurements you've taken from that, and a screenshot of JavaTC showing the simulation parameters and result. Don't forget that scopes tend to have an x axis fine adjust which is easy to mis-set and get the wrong results for period.

It's neither straightforward nor obvious how to put multiple pictures in a single post. Post the second and subsequent pictures to the attachments > pictures_for_use_in_threads thread, edit copy from those to get the links, and edit paste the links into your main post.

I'm kind of assuming that as you amass the actual figures to post, you'll suddenly go 'OMG, spotted it!'

FreakyG

Mon Jul 06 2015, 08:28AM

Registered Member #1734 Joined: Thu Oct 02 2008, 04:07PM
Location: Heemstede, Netherlands
Posts: 8

Hi Chris,

I agree with Dr Slack, we would need more info to figure this out properly, however, I did just plug the figures you provided into JavaTC and got a fres of just over 400KHz. I then added a suitable topload and the fres dropped to 191KHz which seems perfectly within the realms of possibility and eerily close to your measured fres

Regarding your tank cap, I personally do not think that 30nF is large at all. I regularly used my 53nF tank cap for similar coils in the past.

Chris Maness

Mon Jul 06 2015, 02:20PM

Registered Member #55389 Joined: Mon Jul 06 2015, 12:38AM
Location: Grand Terrace, CA
Posts: 29

The test circuit is simple. I am using my signal generator's about across the primary coil, and the scope leads are attached to the secondary. There is no cap currently on the primary. I also used a few turns of wire before I wound the primary, and that gave the same result. I can paste the output of JavaTC here for a clearer picture:

I put my data into another coil program. It says it is resonant at
around 670kHz. Oh my. Not even sure what to think anymore.

J A V A T C version 13.2 - CONSOLIDATED OUTPUT
July 5, 2015 at 10:38:44 PM PDT

Units = Inches
Ambient Temp = 68Â°F

------------------------------------------- ---------
Surrounding Inputs:
------------------------------------------ ----------
100 = Ground Plane Radius
100 = Wall Radius
150 = Ceiling Height

------------------------------------------ ----------
Secondary Coil Inputs:
------------------------------------------ ----------
Current Profile = G.PROFILE_LOADED
1.18 = Radius 1
1.18 = Radius 2
23 = Height 1
38.5 = Height 2
861 = Turns
0.017 = Wire Diameter

---------------------------------------- ------------
Primary Coil Inputs:
------------------------------------------ ----------
Round Primary Conductor
1.5 = Radius 1
4.098 = Radius 2
23 = Height 1
23 = Height 2
7.7947 = Turns
10 = Wire Awg
1 = Ribbon Width
0.1 = Ribbon Thickness
0.006 = Primary Cap (uF)
4 = Total Lead Length
0.01 = Lead Diameter

---------------------------------------- ------------
Top Load Inputs:
------------------------------------------ ----------
Sphere #1: horz=5, vert=5, height=41.5, topload

----------------------------------------- -----------
Secondary Outputs:
----------------------------------------- -----------
673.82 kHz = Secondary Resonant Frequency
90 degÂ° = Angle of Secondary
15.5 inch = Length of Winding
55.5 inch = Turns Per Unit
0.001 inch = Space Between Turns (edge to edge)
532 ft = Length of Wire
6.57:1 = H/D Aspect Ratio
18.9339 Ohms = DC Resistance
23972 Ohms = Reactance at Resonance
0.47 lbs = Weight of Wire
5.662 mH = Les-Effective Series Inductance
6.325 mH = Lee-Equivalent Energy Inductance
6.285 mH = Ldc-Low Frequency Inductance
9.853 pF = Ces-Effective Shunt Capacitance
8.82 pF = Cee-Equivalent Energy Capacitance
18.002 pF = Cdc-Low Frequency Capacitance
3.46 mils = Skin Depth
5.555 pF = Topload Effective Capacitance
94.1658 Ohms = Effective AC Resistance
255 = Q

----------------------------------------------- -----
Primary Outputs:
----------------------------------------- -----------
673.83 kHz = Primary Resonant Frequency
0 % = Percent Detuned
0 degÂ° = Angle of Primary
11.42 ft = Length of Wire
11.41 mOhms = DC Resistance
0.231 inch = Average spacing between turns (edge to edge)
0.261 inch = Proximity between coils
1.01 inch = Recommended minimum proximity between coils
9.199 ÂµH = Ldc-Low Frequency Inductance
0.006 ÂµF = Cap size needed with Primary L (reference)
0.135 ÂµH = Lead Length Inductance
29.719 ÂµH = Lm-Mutual Inductance
0.124 k = Coupling Coefficient
0.124 k = Recommended Coupling Coefficient
8.06 = Number of half cycles for energy transfer at K
5.93 Âµs = Time for total energy transfer (ideal quench time)

------------------------------------------- ---------
Transformer Inputs:
------------------------------------------ ----------
120 [volts] = Transformer Rated Input Voltage
10000 [volts] = Transformer Rated Output Voltage
23 [mA] = Transformer Rated Output Current
60 [Hz] = Mains Frequency
120 [volts] = Transformer Applied Voltage
0 [amps] = Transformer Ballast Current

----------------------------------------- -----------
Transformer Outputs:
----------------------------------------- -----------
230 [volt*amps] = Rated Transformer VA
434783 [ohms] = Transformer Impedence
10000 [rms volts] = Effective Output Voltage
1.92 [rms amps] = Effective Transformer Primary Current
0.023 [rms amps] = Effective Transformer Secondary Current
230 [volt*amps] = Effective Input VA
0.0061 [uF] = Resonant Cap Size
0.0092 [uF] = Static gap LTR Cap Size
0.0159 [uF] = SRSG LTR Cap Size
42 [uF] = Power Factor Cap Size
14142 [peak volts] = Voltage Across Cap
35355 [peak volts] = Recommended Cap Voltage Rating
0.6 [joules] = Primary Cap Energy
361.9 [peak amps] = Primary Instantaneous Current
21.9 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
120.8 [peak amps] = Sec Base Current

----------------------------------------- -----------
Rotary Spark Gap Inputs:
------------------------------------------ ----------
1 = Number of Stationary Gaps
4 = Number of Rotating Electrodes
1800 [rpm] = Disc RPM
0.375 = Rotating Electrode Diameter
0.375 = Stationary Electrode Diameter
10.6 = Rotating Path Diameter

---------------------------------------- ------------
Rotary Spark Gap Outputs:
----------------------------------------- -----------
4 = Presentations Per Revolution
120 [BPS] = Breaks Per Second
56.8 [mph] = Rotational Speed
8.33 [ms] = RSG Firing Rate
13.043 [ms] = Time for Capacitor to Fully Charge
3.19 = Time Constant at Gap Conduction
750.73 [Âµs] = Electrode Mechanical Dwell Time
95.9 [%] = Percent Cp Charged When Gap Fires
13562 [peak volts] = Effective Cap Voltage
0.55 [joules] = Effective Cap Energy
353733 [peak volts] = Terminal Voltage
66 [power] = Energy Across Gap
22 [inch] = RSG Spark Length (using energy equation)

--------------------------------------- -------------
Static Spark Gap Inputs:
------------------------------------------ ----------
2 = Number of Electrodes
1.25 [inch] = Electrode Diameter
0.16 [inch] = Total Gap Spacing

----------------------------------------- -----------
Static Spark Gap Outputs:
----------------------------------------- -----------
0.16 [inch] = Gap Spacing Between Each Electrode
14142 [peak volts] = Charging Voltage
13783 [peak volts] = Arc Voltage
36888 [volts] = Voltage Gradient at Electrode
86142 [volts/inch] = Arc Voltage per unit
97.5 [%] = Percent Cp Charged When Gap Fires
4.942 [ms] = Time To Arc Voltage
202 [BPS] = Breaks Per Second
0.57 [joules] = Effective Cap Energy
359482 [peak volts] = Terminal Voltage
115 [power] = Energy Across Gap
24.2 [inch] = Static Gap Spark Length (using energy equation)

Thanks, Chris

Dr. Slack

Mon Jul 06 2015, 03:31PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

'scope leads attached to the secondary' falls somewhat short of a circuit diagram. But let's try some guesses.

If the scope ground terminal is connected to the secondary ground, and the scope input terminal to the secondary hot, then the resonance you are measuring is the secondary inductance in parallel with the scope's input capacitance *plus the capacitance of your input cable*. That could easily be north of 100pF total, rather more than the 5.5pF you've entered into JavaTC.

Please post a circuit diagram of how you are attempting to measure the secondary resonance.

Chris Maness

Mon Jul 06 2015, 03:52PM

Registered Member #55389 Joined: Mon Jul 06 2015, 12:38AM
Location: Grand Terrace, CA
Posts: 29

Yes, Dr. Slack. After typing the last post, I see that my approach was naive. Especially since the self capacitance is so small with such a large inductance, it would not take much from the scope to pull it WAY down. I will post a schematic in a little while, but your explanation of my scheme tells me you have the right picture.

Thanks for the tip,
I have a fiend that has a large grid dip oscillator capable of resonating down to 220kHz, I can use that or just go with JavaTC's values and see if I can get the coil to break out in streamers with some kludgy caps as a test. I will replace them with commercial caps if I can get the results I like. If there is a problem, I will borrow my friends grid dip.

Thanks a ton,
Chris KQ6UP

klugesmith

Mon Jul 06 2015, 05:24PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Chris Maness wrote ...
... I have a fiend that has a large grid dip oscillator capable of resonating down to 220kHz ...

A good fiend will help you move. A great fiend will help you move a body.

73
RKF

Dr. Slack

Mon Jul 06 2015, 07:00PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

You can still measure the resonance with a scope, just connect it appropriately. For instance, put a capacitor of 6pF between the scope input cable and the top of the secondary, and you'll reduce the load to the 5.5pF you've entered in JavaTC. If you don't have a 6pF capacitor, look up a suitable formula and make one from bits of foil or insulated wire. Put a bit of wire to the scope input as an antenna and waft it in the general direction of the secondary, and you will be able to measure the resonance substantially unloaded.

Chris Maness

Mon Jul 06 2015, 10:42PM

Registered Member #55389 Joined: Mon Jul 06 2015, 12:38AM
Location: Grand Terrace, CA
Posts: 29

I tried the tinfoil and polyurethane sheets. The whole lot rolled and put under cooking oil -- arced over. I then tried a salt water leyden jar with a heavy duty one gallon water bottle with salt. It punched a hole in it after working for a few minutes. It wasn't quite up to the right value for my design. It had 4nF. My design called for 6. I did have enough time to look for a peak going by one whole turn at a time from turn #7 to the last turn #12. When I had it on the last turn. It died almost instantly at that point. Probably punching a pinhole somewhere. I am really surprised because of the thickness of the bottle.

It was loud as HECK and pitted the drawer knobs I am using for my gap.

I am not sure what to do now other than using mason jars filled with salt water. I will need plenty though to get up to 6nF.

Thanks,
Chris

Chris Maness

Tue Jul 07 2015, 02:13PM

Registered Member #55389 Joined: Mon Jul 06 2015, 12:38AM
Location: Grand Terrace, CA
Posts: 29

Update: I used some really large whey protein jugs, and they seem to be holding up. Sparks are no where near the simulators 24". The primary resonates where it is supposed to, but I can only draw 4" sparks and it does break out a little with a screw on top I get 1.5" streamers. I have ordered real capacitors, so will report back when I get those installed.

Regards,
Chris

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