Dr Ronald Stiffler SEC technology

[itsu]

Gyula,

i just wanted to make this BF869 to oscillate with minimum changes in the circuit and now it did i will
leave it at that and continue with the BC337 which stays cool at around 100Vpp output.

I redid my L3 coil and have it resonate at 13.5MHz with the leds connected using my FG as drive.

When i use the BC337 oscillator set at 100Vpp output to drive it then the leds come on faintly, so
more tuning needs to be done.

When i connect a virtual ground (cliplead to the 2 1N4148 diodes center junction), then the leds really
take of, so i will use that virtual ground and tune to the max (5K trimmer pot inserted again as with
direct connect to the 12.5V battery, the oscillator flips to 3th harmonics (40MHz)).

Itsu

[gyulasun]

Hi Itsu,

Thanks and I understand,  okay.

The tuning for L3 in advance by the FG differs from what will be needed from the oscillator output, unfortunately, mainly because the FG output is purely resistive (no reactance). And first, I think, when L3 is connected to the oscillator and the LEDs are also attached to L3, it is the C_var trimmer cap which would need retuning a little first and then L3,  and then the trimmer cap again and so forth. They can mutually detune each other and this should be corrected in alternative steps, the indicator for tuning can be the LED brightness.

It is strange that the oscillator flips to its 3rd harmonic: how can the AC impedance of the collector tank be enough at 40 MHz when it is tuned to 13.5 I wonder.  Can you increase the capacitor value between the base-emitter up to say 50, 70 or even 100 pF? Maybe that will kill amplification at 40 MHz at the transistor input.
Gyula

[Slider2732]

Could the 3rd harmonic situation be related to the early experiments, where an LED in series with the +V input to the crystal lowered it by 3x ?
Example would be a 12MHz crystal that reported as running at 4MHz.
Something about the voltage stability maybe ?


Following a tip by iQuest, i've just got the FFT function going on my Rigol 1054Z.
The idea, is to make use of it with these and related projects.
Dr. Stiffler used to show the FFT output of his experiments and looking at the harmonics might be a clue when changes are made.
Pic attached of where am up to with setting it up...here shown measuring a possible exciter, based on 2 chokes. The FFT display itself is tiny and pressing the Hz/Div only seems to change the Offset, as indeed does the actual Offset button below it.
The scope was 'jailbroken' finally, have never done that and it now reports as a DS1104Z.

Itsu - I know you have been using your FFT and am wondering if your harmonics flip at a specific point of circuit tuning.

[gyulasun]

Hi Slider,

The example you mention: was it a 2 pin crystal or was it a 4 pin crystal oscillator?
I think the two cases are different: the 4 pin oscillators usually need 5V supply voltage +/-0.25V and a LED in series with them may reduce the voltage below the specified range, thus the internal RC coupled amplifier circuit may provide a favorable condition for oscillations at an odd numbered subharmonic of the built-in crystal. (This also depends on the cut of the crystal.)
And inside the casing of the 4 pin oscillator there is no tuned LC circuit while in Itsu's circuit case a single transistor works for high Q toroidal tank which should give additional selectivity for 13.5 MHz, this one thing in itself would show why the 40 MHz frequency is strange to appear. 

Gyula

[itsu]

Gyula,   Slider,

i made a video about my present setup showing the flipping into 3th Harmonics operations etc.
Also the spectrum (0 - 500MHz range) is shown on my Spectrum Analyzer both at 13.56MHz as with 40MHz operation,
see also the screenshots with harmonics table at both situations (the 104MHz at 2th screenshot is a local FM station).

I keep the input voltage low via the 5K trimmer pot to protect my transistor by limiting the collector signal at twice the input voltage, so roughly at about 24Vpp.
If i increase the input voltage it seems the signals get stronger and better (sine wave like), but my transistor won't stand it for long (46Vpp at the collector).

At the end i inserted a 47pF cap across base/emitter, but this does not prevent the oscillator to flip into 3th harmonics operation, even a 100pF cap seems to have no influence.

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

Itsu