B Why does my LC circuit not oscillate its energy between Electric & Magnetic fields?

[Tom.G]

View attachment 351647
If that spectrum is realistic, I suspect that those low resistor values have made the circuit into an RC oscillator.

I recommend that you put the correct resistors (as shown in the simulation) in the circuit; you might actually get the expected results. (The batteries will last longer too.)

Just for grins, change the resistor values in the simulation to the values you actually used. It would be interesting to see what results you get.

Cheers,
Tom

 

[James2018]

View attachment 351647
If that spectrum is realistic, I suspect that those low resistor values have made the circuit into an RC oscillator.

I recommend that you put the correct resistors (as shown in the simulation) in the circuit; you might actually get the expected results. (The batteries will last longer too.)

Just for grins, change the resistor values in the simulation to the values you actually used. It would be interesting to see what results you get.

Cheers,
Tom

Yes, that is what I am going to do, I am going to make a simulation of the actual circuit and see what it does.

 

[James2018]

Oops, seems resonant frequency of my circuit is actually 40 Hertz. In this simulation I used every value for resistor, capacitance and inductance and input DC voltage like in real circuit.

Here is the animation to see AC is present in the tank circuit

 

[James2018]

Antenna oscilloscope - not a pure sine wave, but beats

 

[Baluncore]

The Colpitts circuit you are using has bias voltage dependent on the Re and Rc values.
Here is a different Colpitts circuit, one that I prefer, it uses fewer components and the bias is not dependent on the exact resistance values. Design is for 1 MHz. It has no antenna, the RF output is from the coil current of ±2.7 mA peak, while the circuit runs on less than 0.5 mA.

 

[James2018]

The Colpitts circuit you are using has bias voltage dependent on the Re and Rc values.
Here is a different Colpitts circuit, one that I prefer, it uses fewer components and the bias is not dependent on the exact resistance values. Design is for 1 MHz. It has no antenna, the RF output is from the coil current of ±2.7 mA peak, while the circuit runs on less than 1 mA.

View attachment 351662

And it doesn't matter what resistance values I use, at all? And what values are for capacitance for C1, C2, C3? I don't understand the codes.

 

[Baluncore]

C1, C2, C3? I don't understand the codes.

The convention on circuit diagrams is to move the SI prefix to where the decimal point was. That prevents problems with missing decimal points.
C1 = 0u1 = 0.1 uF = 100 nF.
C2 = 1n0 = 1.0 nF.
C3 = 220p = 220 pF = 0n22.

Keep R1 = R2, at about 33k. Anything from 22k to 47k is OK.
Make R3 about half of R1. 12k to 22k should be OK.

 

[James2018]

The convention on circuit diagrams is to move the SI prefix to where the decimal point was. That prevents problems with missing decimal points.
C1 = 0u1 = 0.1 uF = 100 nF.
C2 = 1n0 = 1.0 nF.
C3 = 220p = 220 pF = 0n22.

Keep R1 = R2, at about 33k. Anything from 22k to 47k is OK.
Make R3 about half of R1. 12k to 22k should be OK.

But my battery cannot deliver currents through resistors with values above 1k. It is not alkaline. I will try but I have to order online these high resistance values they are not found in the local electronics shop. But wait I can make them out of graphite and paper. https://pxt.azureedge.net/blob/fe8d...tutorial/make-a-resistor/clip-to-resistor.jpg

 

[davenn]

But my battery cannot deliver currents through resistors with values above 1k. It is not alkaline. I will try but I have to order online these high resistance values they are not found in the local electronics shop.

Rubbish .... what sort of battery ?

 

[Baluncore]

But my battery cannot deliver currents through resistors with values above 1k. It is not alkaline

Your battery is 5 volts, is it not?
Ohms law applies. It is low value resistors you must avoid.
Your battery may have trouble supplying the current of 45 mA needed for your 56 ohm base bias circuit.

 

[James2018]

Rubbish .... what sort of battery ?

Coin battery... It drains quickly and delivers 15mAh

 

[James2018]

Your battery is 5 volts, is it not?
Ohms law applies. It is low value resistors you must avoid.
Your battery may have trouble supplying the current of 45 mA needed for your 56 ohm base bias circuit.

I will make those high value resistors with graphite and paper. I cannot find them for sale so easily in my country

 

[davenn]

I will make those high value resistors with graphite and paper. I cannot find them for sale so easily in my country

Which country ?

 

[Baluncore]

E12 series resistors from 1 ohm to 10 megohm are everywhere.
What is your country?
https://en.wikipedia.org/wiki/Ohm's_law

 

[James2018]

E12 series resistors from 1 ohm to 10 megohm are everywhere.
What is your country?
https://en.wikipedia.org/wiki/Ohm's_law

Romania

 

[davenn]

Don't you have access to some old scrap electronics... TV's, VCR's etc?
They are a great source for parts

 

[James2018]

Don't you have access to some old scrap electronics... TV's, VCR's etc?

I did fabricate some 16k resistors out of graphite and paper and they worked as indicated my multimeter measuring in resistance mode.
The graphite from a #2 pencil lead will give you somewhere between 5k ohms and 40k ohms of resistance per centimenter.
https://makecode.adafruit.com/learnsystem/pins-tutorial/devices/make-a-resistor

 

[davenn]

I did fabricate some 16k resistors out of graphite and paper and they worked as indicated my multimeter measuring in resistance mode

Not really suitable for what you are trying to achieve.
Surely you have some family, friends etc that have some old gear
you can strip for bits.
I have been doing that since I started in electronics as a kid 55 or so years ago. Am 65 now and still salvage parts from old gear

 

[Baluncore]

If there is somewhere that repairs electronics nearby, they may give you used items for parts.

If there is someone nearby who has many antennas on their house, they might be a member of Federaţia Română de Radioamatorism. They can help you find what you need.

Or contact FRR for an introduction to a local amateur or club.
https://www.hamradio.ro

 

[James2018]

If there is somewhere that repairs electronics nearby, they may give you used items for parts.

If there is someone nearby who has many antennas on their house, they might be a member of Federaţia Română de Radioamatorism. They can help you find what you need.

Or contact FRR for an introduction to a local amateur or club.
https://www.hamradio.ro

There is an electronics shop nearby but they have only resistances between 1 and 1000 ohms. Well, I'll just order them online sometimes.

 

[Merlin3189]

My guess is at about 120 MHz, in the VHF radio band, lasting for less than 1 us.
You might hear a momentary single click from a VHF AM radio receiver.

It would not be visible on a scanning spectrum analyser, because it is too rare, and so would probably not happen at the right time during one sweep.
You could see it on a storage or digital oscilloscope, but only with a scope bandwidth better than 1 GHz, and then only if it triggered and stored in one single sweep.


If you increase the number of turns on your coil from 8, by a factor of 10, to 80 turns, the frequency of resonance will come down by a factor of 10² = 100, into the MW AM broadcast band. You could then hear it in that band, and see it on a low-cost oscilloscope with 20 MHz bandwidth.

If you could arrange a circuit to repeat the resonance at an audio frequency, you could tune in to the resonance frequency and hear that audio tone on an AM radio.

How are you switching the current through the LC circuit ?

My guess is at about 120 MHz, in the VHF radio band, lasting for less than 1 us.
You might hear a momentary single click from a VHF AM radio receiver.

It would not be visible on a scanning spectrum analyser, because it is too rare, and so would probably not happen at the right time during one sweep.
You could see it on a storage or digital oscilloscope, but only with a scope bandwidth better than 1 GHz, and then only if it triggered and stored in one single sweep.


If you increase the number of turns on your coil from 8, by a factor of 10, to 80 turns, the frequency of resonance will come down by a factor of 10² = 100, into the MW AM broadcast band. You could then hear it in that band, and see it on a low-cost oscilloscope with 20 MHz bandwidth.

If you could arrange a circuit to repeat the resonance at an audio frequency, you could tune in to the resonance frequency and hear that audio tone on an AM radio.

How are you switching the current through the LC circuit ?

I think 122 kHz not MHz. The clue is uF. RF tends to come in at pF for VHF.

 

[Baluncore]

I think 122 kHz not MHz. The clue is uF. RF tends to come in at pF for VHF.

I agree, I slipped an engineer's order of magnitude in my estimate.
But why quote it twice?
For so few turns on the inductor, the capacitance was ridiculously large and resistive.

 

[James2018]

I agree, I slipped an engineer's order of magnitude in my estimate.
But why quote it twice?
For so few turns on the inductor, the capacitance was ridiculously large and resistive.

I assembled your circuit with the 33k and 15k resistors and the BC547B transistor, but I kept the values in the resonant LC to the original effective capacitance of 50 nF and effective inductance to 1.35 uH, I did not use 220 pF and 1 nF and 120 uH because I want to keep the original frequency of 612.6 KHz. I will test the radio AM reception soon, when I am not busy.

 

[Baluncore]

... because I want to keep the original frequency of 612.6 KHz.

I don't think the frequency is 612.6 kHz, because if it was, you would hear the quiet spot there with the AM radio.

You need to wind a coil with the correct inductance to oscillate at 1 MHz, that is the mid-point of the BC band. You can then have 60% errors, and it will still be in the AM BC band.

 

[James2018]

no problem I will increase the coil length of the variable inductor so it can have 0.506 uH instead of 1.35 uH to get a resonant frequency of 1.001 MHz.

 

[James2018]

I don't think the frequency is 612.6 kHz, because if it was, you would hear the quiet spot there with the AM radio.

You need to wind a coil with the correct inductance to oscillate at 1 MHz, that is the mid-point of the BC band. You can then have 60% errors, and it will still be in the AM BC band.

Problem, this time no detectable voltage is reaching the inductor (yellow tube covered in tape) at all. May be under 0.1 milliAmperes, the transistor is correctly connected as I know and the resistances are all the right values and connected like in your diagram.

 

[Baluncore]

Problem, this time no detectable voltage is reaching the inductor (yellow tube covered in tape) at all.

The coil is grounded at one end, and DC isolated at the other with two capacitors, C1 & C2, so it should have zero DC voltage.

This circuit oscillates with a high signal voltage, about half the battery voltage, so that might make voltage measurements with a DMM difficult.
Check the base voltage is half the supply.
Check the emitter voltage is about 0.6 volts below the base voltage.

Build your circuit over a sheet of paper, so you can write clear values against components, and C B E against the transistor.

Compute the inductance. I cannot see the coil detail. What is the number of turns on the coil? What diameter, and how long is the coil?

 

[James2018]

The coil is grounded at one end, and DC isolated at the other with two capacitors, C1 & C2, so it should have zero DC voltage.

This circuit oscillates with a high signal voltage, about half the battery voltage, so that might make voltage measurements with a DMM difficult.
Check the base voltage is half the supply.
Check the emitter voltage is about 0.6 volts below the base voltage.

Build your circuit over a sheet of paper, so you can write clear values against components, and C B E against the transistor.

Compute the inductance. I cannot see the coil detail. What is the number of turns on the coil? What diameter, and how long is the coil?

37 turns (not counting the half turns at the legs of the coil), 6.4 cm long, 0.8 cm diameter. I made one bad connection in the circuit, the wires are NOT supposed to touch where the red circle is, right?

The simulation shows that if the wires touch there, a "capacitor loop with no resistance" forms and no current flows. If the wires don't touch there, everything is working.

 

[Averagesupernova]

I made one bad connection in the circuit, the wires are NOT supposed to touch where the red circle is, right?

Of course not. What would be the point of this? Think about how the transistor works and why that connection would be wrong. At this point I would have hoped you would understand this.

 

[James2018]

Of course not. What would be the point of this? Think about how the transistor works and why that connection would be wrong. At this point I would have hoped you would understand this.

Don't worry, I fixed the circuit.