Mysterious Resonant Circuit

[aleks]

@aleks

I'm sure you understand that actual work being done is not limited to things as tangible as a weight being lifted. Conversion of an energy to heat or another energy is a valid form of work. Similar to what Eldarion stated... in a carbon resistor little will change until heat extremes are met or the frequency applied is so high that the inductance of that resistor and the leads must be considered.
I dislike having to deal with the complexities of pulsing and alternating signals but it is a simple fact of life with electronics. Accuracy with these signals causes problems for more than the layman.

Well, I think you are missing one thing (or maybe I'm mistaken on it), is that resistor not necessarily converts all current into heat. I see it pretty wrong to equate power going along resistor to heat it dissipates. After all, the only purpose of resistor is to provide resistive path to current. This, in turn, simply disfavors one energy path in comparison to another energy path: this can be seen as returning part of the energy back to the previous segment of the circuit while dissipating a bit of it as heat as well. A segment of wire may have a high power going along it, but only a bit of it turning into heat. And of course, motor is not the only thing that can be used. You may use some special calorimeter, or put a LED and measure its light energy output.

[duff]

Hi Duff,

EMDevices wrote about his coils number of turns in the 1st page of this thread for you:

So eventually you have used the same because Peter also used EMDevices's turns numbers as he wrote.

Regarding your waveforms shown in the previous page I think you have two oscillations of different frequencies in the same oscillator circuit.  This is not unusual in HF oscillators where there are at least two frequency selective networks or pair of components. 
The first is I think the R2C1, this gives the lower frequency oscillations (this is about the 20us time (4 * 5us)). (Notice the value of C1 is modified by the base-emitter input capacitance which from the 2N4401 data sheet can be max 30pF, for a Philips made such transistor, http://www.nxp.com/acrobat_download/datasheets/2N4401_4.pdf ).

The second is your 8.2uH base feeding coil L1 together with C1 + also the base-emitter input cap value, I think this constitutes the higher frequency operation of around 16 MHz as your digital meter in the oscilloscope shows.

Because the waveforms from EMDevices or Peter do not show a two frequency operation I think the lower frequency operation cannot occur in their circuits due to smaller loopgain or feedback for that lower frequency but in your circuit it can.
Mannix reports he has not used ferrite cores (if I understood it right) so this explains why his wire lengths affect so much the frequency (without ferrite core the coils has much less inductances).  He has not reported on the double frequency oscillations but he can see this with a scope only.

Regards,
Gyula

@gyulasun

Woh - I missed EM's response. I believe he did an edit on that post and I never read again after the initial posting. Thanks for pointing that out.


I see what your saying with regards to the base emitter capacitance however when I had the 0.01uF in the circuit I saw the same effect.  Don't you think the .01uF cap would have swamped out the junction capacitance?


-Duff

[pese]

I, and many other engineers, have used these carbon film resistors in VHF radio equipment--they do not change value by any significant amount, even at 144Mhz.  If the measurements of resistor voltage were taken with the scope probe and scope ground attached close to the resistor body, then the results are definitely valid.

Eldarion

any metal film or carbon resistor is inductive IF there surface is not
tublar (outside an ceramic or glas body. or even it is an comosite resistor
(as usual in 1959 60 and longer is USA. that was and carbon powder tat is pressed in the middle of an plastic (bakelite) tube.

most resitors NOW are withe an carbon (or metal) surface that is windeing (as snake) outside and zylindiic body. So the are inductuctive with mostly 5 to 10
turns on the body.
THAT MAKE INDUCTIVITY  that will even make problems in some FM circuits,
but it can used also if an small choke is needed, and can replased with an resitor.
(some oszillator circuits, even low-power trnsmitters , will work this way)
Pese

[xee]

@ duff
You were not asking me, so I hope I am not cutting in. But I suspect the 0.01 uF capacitor acts like an RF short-DC block. The reactance of the 0.01 uF capacitor will be very low so when added in series with the higher reactance from the transistor it will have little affect on the resonant frequency. I hope that explanation makes sense.

[duff]

@ duff
You were not asking me, so I hope I am not cutting in. But I suspect the 0.01 uF capacitor acts like an RF short-DC block. The reactance of the 0.01 uF capacitor will be very low so when added in series with the higher reactance from the transistor it will have little affect on the resonant frequency. I hope that explanation makes sense.

@xee

Not a problem -

Actually you guys have helped a lot - Thanks!


-Duff