Dr Ronald Stiffler SEC technology

[itsu]

While waiting for "the next step", i made a comparison between my just received SMD Schottky diodes (mbr0520lt1G
20V, 500ma) and the earlier used 1N4148 diodes.

These SMD diodes have a Forward Voltage drop of 140mV measured with my Fluke DMM (diode test setting) and
the 1n4148's measure around 600mV, so for a 14 diode ring this means a total difference of 7v (9V versus 2V).

The leds behave differently with the schottky diodes, the resonance peak frequency is much lower (4.6Mhz) and less
broad, depending if i have attached the DMM for measuring the voltage (18.05V).
Also the white cliplead to the back of the leds has to be there.

With the 1N4148's, the resonance frequency is higher (7.2MHz) with or without the DDM leads and much broader,
but the leds are not that bright on as the voltage across them is about 17.65v.

I used my FG for these tests as with the Xtal osc. it ran only with the 1N4148 diodes (13.56Mhz), not with the schottky's.
Using some lower frequency Xtals (4.4Mhz , 3.5Mhz, 6mhz) made some difference, but adding any DMM lead or scope
probe killed the leds, so i was unable to make some readings.

So we do not see the 7V Forward Voltage drop difference having much effect as probably its being smoothed out by the leds
(zener effect?).

Video here: https://www.youtube.com/watch?v=ZdgvmFIAkQw


Gyula,  i have seen your earlier comments, i will reply to them tomorrow.


Itsu

[gyulasun]

Hi Itsu,

You wrote: "So we do not see the 7V Forward Voltage drop difference having much effect as probably its being smoothed out by the leds (zener effect?)."

Yes, the smaller voltage drop can mainly manifest in the loop as an increased current (the LEDs brightness increased) because of the voltage limiting LED characteristics (they are relatively good Zener diodes). If you feel like doing, compare the currents in the loop when the Schottky and when the 1N4148 Si diodes are used (driving them from FG).
If not the LEDs were used as the load in the diode loop but say a linear load like a resistor, then the 7V difference could be measured more readily across the resistor, depending on the load current, of course (forward diode drops are current dependent).

It is interesting the frequency went down when the Schottky diodes were used, this might be explained by their much higher self capacitance in the reverse direction, see Figure 3 in data sheet: https://www.onsemi.com/pub/Collateral/MBR0520LT1-D.PDF   Unfortunately, no switching time is specified for this diode, although they recommend it for high frequency rectification, probably very good for up to some ten kHz to rectify with low voltage drop.

Thanks for testing this diode type, I appreciate your kindness.

Gyula

[itsu]

Hi Itsu,

I wonder why your setup peaks around 9 MHz when driven from the FG instead of the 13.5MHz the oscillator provides, the difference sounds too high at first.

Could it be due to the oscillator output being a high impedance source while the FG has the usual 50 Ohm low impedance output and the "shunting" effect of the latter via the overall stray capacitances of the 'enviroment'  (the lattice as the Doc would put it) can have such a high detuning behaviour? Well, maybe this is the case.
I assume that none of two L3 coils can be tuned individually by a small piece of ferrite rod to increase brightness any further, once the oscillator tank capacitor is set to the maximum light: this would insure the two L3 is in resonance around 13.5 MHz.
In case the coils would need tuning towards a little higher frequency, then try to use a piece of Alu or copper rod (say with a few mm OD and 10-15 mm long) because they will have the effect of increasing coil resonant frequency (versus the normal decreasing effect of a ferromagnetic core).
And if this same could be found for the case when the FG drives the two L3 coils, then my assumption would be correct, otherwise not.

Notice in the Doc's latest video the two L3 coils are placed far enough from each other length wise, your coils have parallel axis, this gives higher chance for mutual coupling than that the Doc's coils position. I mean there is a higher 'built-in detuning' possibility in your arrangement for the two coils (but this may not be a drawback).

Thanks for the video.

Gyula

Gyula,

i think when putting 2 coils in series, the inductance adds up, so the total inductance becomes 2x 27uH = 54uH.
This will cause a lower resonance frequency when the capacitance stays equal (13.6 becomes 9MHz).

As i mentioned in the SMD diode post, the double L3 resonance peak (the range in which the ledstrip is lighted),
is very broad covering between 7 to 15Mhz with the 1N4148's.

So the Xtal osc at 13.6Mhz was able to light the ledsstrip (1N4148 diodes), but when fine tuning using the FG it
peaked the lighs around 9 and 7.7Mhz.

I did not try to tune the both L3 coils, but i was looking if there is some change when moving the both vertical
L3 coils to or from each other.
Only when they are almost touching each other (so very close) there is a change for the better (mutual coupling).

I did at first try with the both L3 coil laying flat on the bench like Dr Stiffler did, but the effects were the same.

I will try some of your suggestions tonight, including the current measurement.


Thanks,   Itsu

[gyulasun]

Hi Itsu,

Okay on the total inductance in series connection, they add up indeed and normally the result is the sum of the two IF there is no mutual coupling between the two coils. From this, two things may come:

to maintain the 13.56 MHz resonant frequency for two coils in series, what if the individual coils are reduced in advance to around 2 x 13.5 uH ?  Will they give the quarter wave voltage maximum at their top when fed with 13.56 MHz? 

The other thing is the effect of mutual inductance, as is the case with your two coils much closer to each other than in the Doc's setup, it increases (or reduces) the sum of the two inductances.

It is the magnetic coupling which can make the tuning very broad, it is ok that maximum brightness comes when you place the coils very close (almost touching) each other but how the quarter wave resonance may develop at the top of the coil is a good question in that case.
Of course I do not mean you reduce the number of turns for the two L3 coils and check them at 13.56 MHz. All I mean is the use of 2 coils in series may make tuning more complex. 

Gyula

[tinman]

All--I'm not sure now that a 'Ring Modulator' is like the 'Stiffler Loop'.  The Ring Modulator (like Gyula mentioned) is all about mixing two input signals.  We are dealing with just one here.  It was perhaps a trip down a rabbit hole. That was an interesting idea but maybe a waste of time to pursue that explanation.

Slider----Yep.  If Doc lights up an LED panel stuck in the ground more than about 6 inches away from the SEC----- I will be surprised also.

---Lidmotor

6 inches 
I'll give you 6 feet at a frequency of just 100KHz

I see ya'll still using diodes 

Meet Mista Transista
10V P/P-->100KHz 
Duel inductive bass drives,with double junction capacitive enhancers 

Whens the challenge start?


Brad