Hello, can somebody check my transistor amplifier schematic?

[Baluncore]

Sir you kno what i make it, i remove the filteres and they work? WITHOUT FILTER

That is a very wise move.

I modeled the filters yesterday to find the low pass frequency and the design impedance of the interface. I found that they got something wrong in their design but I have not worked out what their mistake is yet. The more I look at that paper the more suspicious I am that it was a typical student exercise. Maybe they got the phase and amplitude swapped on their transfer function?

 

[Mark Harder]

I don't know enough electronics to answer this myself. But I was wondering if the set of uncoupling caps on the 12V supply is adequate to remove any couplings of oscillations between the transistor collectors. Are these arbitrary? Or do their values and placement affect performance significantly?

 

[michael1978]

That is a very wise move.

I modeled the filters yesterday to find the low pass frequency and the design impedance of the interface. I found that they got something wrong in their design but I have not worked out what their mistake is yet. The more I look at that paper the more suspicious I am that it was a typical student exercise. Maybe they got the phase and amplitude swapped on their transfer function?

GOODMORNING;They make mistake, i don't know i am not a specialist, but when i remove all lpf, is working but frequency i think is 150mhz, but leave forgetit i make you tired, i going to do it one man he show me how to do it, i feel bad because, i make to much bussi with this oscillator leav it, i make one, which one man he told me. Ok Thank a lotsssssss Have a nice wekend.

 

[michael1978]

I don't know enough electronics to answer this myself. But I was wondering if the set of uncoupling caps on the 12V supply is adequate to remove any couplings of oscillations between the transistor collectors. Are these arbitrary? Or do their values and placement affect performance significantly?

i am either not specialist

 

[Baluncore]

Are these arbitrary? Or do their values and placement affect performance significantly?

They are critical. Those capacitors are not important to simulation but they are shown so they will not be forgotten when a real circuit is built.

One big problem with amplifiers, especially RF circuits, is when the output currents get back to the input stage which can then cause oscillation. So the design of the power supply as a low pass filter is as important as the design of the signal path.

It is important that multiple capacitors of different construction are used to bypass the supply. Electrolytics are slow and have high inductance so will need a faster capacitor closer to the circuit. Inside the circuit where active components connect to the power supply there will need to be fast ceramic capacitors, say 1nF.

 

[michael1978]

They are critical. Those capacitors are not important to simulation but they are shown so they will not be forgotten when a real circuit is built.

One big problem with amplifiers, especially RF circuits, is when the output currents get back to the input stage which can then cause oscillation. So the design of the power supply as a low pass filter is as important as the design of the signal path.

It is important that multiple capacitors of different construction are used to bypass the supply. Electrolytics are slow and have high inductance so will need a faster capacitor closer to the circuit. Inside the circuit where active components connect to the power supply there will need to be fast ceramic capacitors, say 1nF.

Thank Your Sir

 

[michael1978]

They are critical. Those capacitors are not important to simulation but they are shown so they will not be forgotten when a real circuit is built.

One big problem with amplifiers, especially RF circuits, is when the output currents get back to the input stage which can then cause oscillation. So the design of the power supply as a low pass filter is as important as the design of the signal path.

It is important that multiple capacitors of different construction are used to bypass the supply. Electrolytics are slow and have high inductance so will need a faster capacitor closer to the circuit. Inside the circuit where active components connect to the power supply there will need to be fast ceramic capacitors, say 1nF.

sorry i come back one more time to you, now is working like your, because i was making exmperiments and i did, just the frequence i don't know they change from 90MHZ to 95MHZ, i don't know how to repair this one

 

[Baluncore]

1. I have no idea what you are wanting. What is broken? When did it last work OK? Are you considering an Ltspice or a SIMetrix simulation? Please give a link to the relevant circuit.

2. You do not have to quote a complete post to reply. Select the relevant part of the post, then right click to quote that small part only.

 

[michael1978]

1. I have no idea what you are wanting. What is broken? When did it last work OK? Are you considering an Ltspice or a SIMetrix simulation? Please give a link to the relevant circuit.

2. You do not have to quote a complete post to reply. Select the relevant part of the post, then right click to quote that small part only.

No my question, was the circuit you make it in LTSPICE, i make yesterday the same in SIMETRIX, i study your circuit in LTSPCIE,, after my circuits from yesterday is working perfect, Only the tuning is not working when i put probe to the cathode it changes the frequence from 90 to 100Mhz, i mean when i change the voltage at for .8V to 6.5V (is that normal working)?
here the circutis

 

[Baluncore]

You have tangled the varicap circuit.
I believe that your C4=42pF cap was used to represent the varicap circuit.
Remove C4=42pF.
Remove C10=100pF.
Connect varicap D1 cathode, to the open bottom node of L1.

Don't forget to remove the LPF.

 

[michael1978]

You have tangled the varicap circuit.
I believe that your C4=42pF cap was used to represent the varicap circuit.
Remove C4=42pF.
Remove C10=100pF.
Connect varicap D1 cathode, to the open bottom node of L1.

Don't forget to remove the LPF.

Goodmorning sir, i did not remove the c10(47p), because is not working, C4 i and lpf i remove, now with 2V is output 88MHZ AND 6.5V is 108Mhz, output to emitter of q2, thnx man