Your load (R2) is 2k. Reactance of L1 is 628Ω.
But for frequency stability and for reliable excitation
reactance of L1 should be lower as much as possible than R2.
Selected 50 nH has reactance 31.4Ω.
So 2000 / 31.4 ≈ 64.

Pay attention to value of V1 in circuit right to green curve.
It is 12V.

These resistor and capacitor are important in real circuit, but not necessary for simulation.

With changed values of capacitors C3, C4 feedback power goes to emitter is not enough for oscillation.

Circuit works with capacitor C4=1μF, but it takes about 10ms for beginning oscillation,
because of long charging time through resistor R5 51k.
===================
Below see reliable and frequency stable circuit, which works with load 2k.

View attachment 191096

Thank you, will change inductor and make changes.. didn't pay attention to voltage source sadly. trying shortly but why did you do 2000/31.4? thinking should be doing parallel combination but okay : learning more today : question getting more stupid

In my example, I used the CQ1 parameter - the average transistor capacity on the collector side. The collector capacity of this transistor (from the spice model) is 4 pF at zero offset. In this generator, the voltage is greater than zero and the average collector capacity is accordingly smaller. I have set 3 pF, although this capacity is likely to be smaller. I also added the entire capacitance of the feedback capacitor to the total capacitance of the resonant circuit, although it is more correct to attach an equivalent capacitance equal to the capacitance of two consecutive capacitances. This would also reduce the total capacity of the resonant circuit by about 0.4 pF.
I have made a rough calculation of the inductance of the coil. I used COIL64 (Coil32) to calculate the coil. This is a good program (multilingual) and I suggest you use it. The result is a small coil of three turns. View attachment 191106

Thanks I see little better now


Missing a lot of things in understanding
and sorry but what's the CQ1 in the transistor as you say is different from feedback capacitor? how did you see it is 4pf at zero offset?

Maybe missing something : Q in program of your work is 209

 

Yes, Q in program of your work is 209.
At first, I made a preliminary calculation and proceeded from the typical qualities of inductance. If I had taken a thinner wire and a smaller coil diameter, I could have obtained a lower Q-value (or a higher serial resistance).
But the dependence of the collector capacity on the voltage.

 

Your load (R2) is 2k. Reactance of L1 is 628Ω.
But for frequency stability and for reliable excitation
reactance of L1 should be lower as much as possible than R2.
Selected 50 nH has reactance 31.4Ω.
So 2000 / 31.4 ≈ 64.

Pay attention to value of V1 in circuit right to green curve.
It is 12V.

These resistor and capacitor are important in real circuit, but not necessary for simulation.

With changed values of capacitors C3, C4 feedback power goes to emitter is not enough for oscillation.

Circuit works with capacitor C4=1μF, but it takes about 10ms for beginning oscillation,
because of long charging time through resistor R5 51k.
===================
Below see reliable and frequency stable circuit, which works with load 2k.

View attachment 191096

See
View attachment 191099

Made both circuits on copper clad board but not working : really annoying and no knowledge gained in sodering

Although after making 2nd circuit which i did first (almost same as my original): touching scope probe made the circuit oscillate with about 0.5v pk-pk and was about 68Mhz (c1 was reading 25pf but other capacitors were close to normal value)

After making Danko's circuit (after long soldering and hoping for oscillation) : did not work : first circuit stopped working too even though touched probe

Frustrating : need oscillation

Checked connections and everything seems fine but surely making mistake but dunno..Anything to check?

Guess back to study and later start with 10Mhz and go from there

Really doubt can make sense from images but maybe is construction technique problem : anyway could have done it better?
measured the base and emitter voltages and checked out with theory

But thanks for your helps : but need oscillation

 

As shown in the last few posts, the transistor characteristics have quite an effect on the operation of this circuit. That is another reason to consider other circuits where the device characteristics have less effect. In the real world device properties do vary both with temperature and age and also through production runs. As soon as you build a second copy that starts to matter. That is a good reason to choose a type of circuit create to minimize dependence on transistor properties.

 

But thanks for your helps : but need oscillation

A.
1. Seems too long wires/leads.
2. Temporary use C3 and C4 both 6.8p.
3. Measure by probe 1:10.
4. Connect probe to emitter (mark "Osc").
B.
5. Connect probe to R5. If no oscillations, then solder resistor R_test and connect probe to Osc2.
6. Rebuild coil L1. It should be 2 turn with inner diameter 5mm for 100 Mhz.

 

Hello,

Perhaps you could try the "manhattan style" prototyping.
The attached PDF will give you more info.

Bertus

 

Another approach is to just wire the components together keeping the leads a short as you possibly can. No circuit board at all, and make it tiny. I have done this a few times over the decades and it has always worked.

That little yellowish lump at the left end of the battery holder is the FM transmitter. No circuit board, not plastic breadboard, only the components connected to each other.

By the way, in case it is helpful, below is the circuit of this particular transmitter. The transistor can be a 2N3904.

 

1. Seems too long wires/leads.
2. Temporary use C3 and C4 both 6.8p.
3. Measure by probe 1:10.
4. Connect probe to emitter (mark "Osc").

View attachment 191140

The string C6 and R5 will very effectively prevent any oscillation. Why are they there? what is their intended purpose?
And note that this does not look that much like any colpts oscillator that I have seen. Where do these circuits come from?

 

1. Seems too long wires/leads.
2. Temporary use C3 and C4 both 6.8p.
3. Measure by probe 1:10.
4. Connect probe to emitter (mark "Osc").

View attachment 191140

Yes changing C4 to 6.8p made difference and measuring from emitter

Like Bordodynov's circuit the oscillation could see at 64Mhz while touching probe can see it here but at 25Mhz but less pk-pk but given up on 100Mhz for now....read a bit then do 20Mhz then advance little by little

Hello,

Perhaps you could try the "manhattan style" prototyping.
The attached PDF will give you more info.

Bertus

Thanks : upgrading to this nearest future

As shown in the last few posts, the transistor characteristics have quite an effect on the operation of this circuit. That is another reason to consider other circuits where the device characteristics have less effect. In the real world device properties do vary both with temperature and age and also through production runs. As soon as you build a second copy that starts to matter. That is a good reason to choose a type of circuit create to minimize dependence on transistor properties.

There are lots of 100Mhz on google but understand your point: like you're reading my book : section on stability with temperature

 

can see it here but at 25Mhz but less pk-pk

Good. See instructions in post #25, section B.

And note that this does not look that much like any colpts oscillator that I have seen. Where do these circuits come from?

These circuits are from Colpitts, modified by me.
Changes is in addition resistor between emitter and feedback capacitors.
This resistor eliminates distortion of oscillations, when emitter resistor is lowered for increasing power of oscillations.

The string C6 and R5 will very effectively prevent any oscillation. Why are they there? what is their intended purpose?

This string imitates outer resistive load for oscillations. Resistor R5 consumes only 1/64 of bank reactive power.
Not so much.

 

was trying to learn more

B..seems like changing the coil removed oscillation or reduced amplitude that can't see

which transistor will work better than 3904 in this? 4401?

Actually it is oscillating at the emitter but really low amplitude like before...86Mhz
and you meant *10 on probe right?

but why really low amplitude?

 

Reducing the positive feedback will reduce the amplitude but more important is it also reduces the distortion. and distortion equates to harmonic content.

 

What is the input capacity of your input divider? This parasitic capacitance can greatly change the circuitry setting. That is, by climbing into the circuit with an oscilloscope, you can change it drastically compared to the circuit in the simulator. Also determine the load. If it is a small (short) antenna, its impedance is capacitive. There are formulas for calculating this capacity. If the load impedance is about 2 k", as shown in some of the above diagrams, a buffer stage is required. Also if you want to see which frequency, connect an oscilloscope to the circuit via a small capacitor. For example, 1 pF. Or, as I did, I wrapped a small spiral around the oscilloscope input with an insulated wire and connected the two ends of this wire to the control point. You will be observing a small signal, but you will remove the influence of the oscilloscope on the circuit. You can simulate the effect of an oscilloscope in a simulator by replacing the oscilloscope with an equivalent capacitance.

 

1) Eelctrolyte never is capable to work any above few kHz, thus must add the certain cermic cap into Vcc
2) Base of bjt must be grounded for AC by means of some ceramic cap. Spice may misapply the voltage source parameters in such meaning, just put the cap on there
3) The distorted form of oscillations is clear sign that positive loop is too strong and tank Q-factor is too weak. Just diminish the collector to emitter capacitance until broken oscillations and then slightly increase it to renew generation. If still the form is not good enough, then take a measures to increase the conture Q-factor.

 

was trying to learn more

(Some text removed for clarity)

which transistor will work better than 3904 in this? 4401?

Of the two the 2N3904 is a little more likely to perform well because its rated FT is a little higher than the 2N4401. In most applications you might also have to look at noise figures and the emitter current at which FT is specified to determine which one offers an advantage if any.

 

Another approach is to just wire the components together keeping the leads a short as you possibly can. No circuit board at all, and make it tiny. I have done this a few times over the decades and it has always worked.
View attachment 191147
That little yellowish lump at the left end of the battery holder is the FM transmitter. No circuit board, not plastic breadboard, only the components connected to each other.

By the way, in case it is helpful, below is the circuit of this particular transmitter. The transistor can be a 2N3904.

View attachment 191149

Thanks : for this your circuit what is the inductance? want to test analytic skills

Also is there any way to know what base voltage is going to be before hand? no right?

and for transistors, seems 2n5179 will do a great job

 

Actually it is oscillating at the emitter but really low amplitude like before...86Mhz
and you meant *10 on probe right?
but why really low amplitude?

Check probe. It should be "x10".
In oscilloscope setting set for channel you use:
1. Fullband
2. Probe Rate: x10
I built test circuit and was trying to find method for HF collector voltage measuring:

Almost have not parts, therefore tank capacitor C2 is 100p and feedback capacitor C3 are DIY, with unknown capacitance.
D1 and C4 added for amplitude collector voltage measurement.
HF p-p voltage = 2 * (0.5 + (V_dmm - V1)).
Measured V_dmm in test circuit is 20.6V, so HF Vp-p = 18.2V.
In process of V_dmm measurement oscilloscope probe should be removed from circuit.
Current, consumed from V1 is 5.5mA
and 16mA, when no oscillation (iron rod inside L1).
Voltage on emitter - see emitter.png.

 

Check probe. It should be "x10".
In oscilloscope setting set for channel you use:
1. Fullband
2. Probe Rate: x10
I built test circuit and was trying to find method for HF collector voltage measuring:
View attachment 191371
D1 and C4 added for amplitude collector voltage measurement.

Nice... don't understand d1 and C4...learned a bit today how to analyze
Just did one and soldered : about to test it

Will do tonight...D1 for ? limiting amplitude? some oscillators have diodes at FET gate : for what?

and is that diy capacitor or diy inductor?

 

Both inductor and capacitor are DIY. Arrow pointed to capacitor.
Diode D1 and capacitor C4 served for HF voltage measurement only.
We can not see HF voltage by oscilloscope, but may accurate measure it by this way.

 

We can not see HF voltage by oscilloscope, but may accurate measure it by this way.

hmm don't understand

and that arrow is pointing to capacitor? is capacitor not 2 metal plates seperated by insulator?
looks like inductor but okay : inductor wires have capacitance maybe

in your circuit, what will C3 be for 100Mhz getting about 102pf which is really close to c2 as 100pf but okay...testing

oh , understand D1 nd c4...like rectifier ; get the peak voltage

Unfortunately after first try, circuit not working for me : mistake

I give up
Thanks