Dr Ronald Stiffler SEC technology

[gyulasun]

Hi Slider,

Yes, quasi any kind of coil having any inductance from say 20 uH to 100 uH or higher could help increase the impedance in the collector. This is a good reason again to visit the shed...     to find some RF coils on that board with the many crystals.
If you find that such a coil causes only a little increase in collector voltage amplitude (monitorod on your scope versus the negative rail),  then connect some more similar in series. 
You can also use that coil you refer to, if nothing else.  Or if you have an RF type ferrite core, then just wind 20-30 turns on it from any enamelled wire and see the amplitude. Radial or axial type chokes are also useable here.

What is the output unloaded amplitude of your AD9850 sig gen around this 13 -14 MHz?

[itsu]

Playing around with my 3 coil setup.

Now measuring not the input, but the output to the led strip.

Using the FG it turns out that i have 18V dc across the leds turning them on faintly.
I compared with another similar led strip attached to my PS set at 18V dc.

Lateron switching over to the crystal oscillator instead of the FG.
It will not light the leds directly attached to the 3 coil setup, only via a capacitively
coupled setup (double sided PCB touching the input wire isolation).

The output on the led strip is the same as when on the FG, like about 18V dc.

Screenshot shows the purple and blue signals being the plus and minus side of the led strip,
with red the math function blue - purple to show the resulting DC voltage (18V).


Video here:  https://www.youtube.com/watch?v=ac51I-cdMbE&feature=youtu.be

Itsu

[gyulasun]

Hi Itsu,

The 18V DC is created by the AV plug diodes across the LED diodes (7 LEDs in series and this is in parallel with another 7 LEDs also in series). You know the voltage - current characteristics of LEDs are like that of Zener diodes hence the 17.8 to 18 V DC level automatically developes across the array (LED string).   Seemingly the basic 3 V forward voltage for a single white LED is not valid here because 18V / 7 = 2.57 V only, instead of the 2.9V to 3.3V range but I think this lower value comes from the parallel connection of the two series strings. (like for Zeners or for normal diodes the parallel connection does reduce the original Zener breakdown or forward voltages)

If you connect two such LED boards in series to add their '18V levels' and feed them with the AV plug, then the input RF energy may be able to light them both, albeit they maybe would not have similar brightness than in the single board case. And you would then see a 33-35V or so DC on the scope Math. 

By the way, I assume if you connect an electrolytic cap across the DC wires of the LED board with the correct polarity, then it would serve as a puffer capacitor for the AV plug diodes and maybe you could check the DC level not only with the scope but with a normal DC voltmeter. A 47 to 100 uF, 25 or 36 V rated electrolytic would be ok for such test. (Notice: if you remove the LED board from the puffer cap, then a 160V DC rated capacitor should be used to handle the unloaded DC level from the AV plug.)

Regarding the need for a capacitive coupling when the xtal oscillator drives the 3 coils instead of the FG, I think also the input of 3 coils may represent a low impedance and loads down too much the toroidal tank. Perhaps you can see this on the scope what happens to the near 100 Vpp across the toroidal tank when you attempt to drive the 3 coils.

Could you use a low pF value trimmer capacitor instead of the PC board? I mean a few pF, max say 10 pF. To make the tuning of such capacitor relatively hand_effect_detuning free, you could make a 'trimmer cap' by twisting two enameled wires together, say you make a 10 cm long twist and leave the 2 wires open at one end. Then connect the two other wire ends as a coupling capacitor between the tank and the 3 coil setup. To tune such capacitor, just cut down the open end of the twist gradually say by 1 cm or half a cm at a time and see the brightness.

Nice experiment by the way, thanks for showing.  Would have one question: what is the LED board current when you drive it from the power supply 17.8 V DC?

Gyula

[itsu]

Gyula,

thanks for the comments, i will digest them later this weekend.

The question you have i can answer, as the current pulled by the PS at 17.8V was 2.2mA.

Measuring the current from the battery feeding the oscillator was fouled up by RF? as i could not get
a correct reading.

itsu

[Slider2732]

And another reply for Gyula
A 100uH axial inductor was tried and unfortunately has pulled the output further down.
Will try various other methods, including winding on a ferrite core and seeing how the output changes with increasing winds. Will start at 1 turn.
Sorry about the delay, been publishing books. That's 4 in the past few days, 2 of them today.

Here are 2 scope shots.
The first is the 13.5225MHz 2 pin crystal circuit output running through the boost circuit.
The second is the AD9850 at 13.6MHz.
Scope probe is on the 100uH output from the Collector, other end is on the Ground of the boost circuit.