Hi, how to make 2 IF from one IF amplifier circuit, to get higher gain

[michael1978]

Hi, i take one If amplifier, from internet and i want to make the second the same, but i don't know how to couple, of what i need to do, to get more gaing
can somebody help me?
here is one IF amplifier in ltspice, rename in asc, or remove only txt extesion.
and what is the best to do, is for fm receiver?

 

[berkeman]

Can you post a PDF screenshot of the circuit? That way I don't have to load your file into my SPICE simulator to be able to reply. (use the UPLOAD button in the lower right of the Edit window)

Also, are you meaning to convert to two different IFs to get the higher gain? It's probably not a good idea to series-connect two amplifiers working at the same frequency (stability can be a practical problem)...

 

[michael1978]

Can you post a PDF screenshot of the circuit? That way I don't have to load your file into my SPICE simulator to be able to reply. (use the UPLOAD button in the lower right of the Edit window)

Also, are you meaning to convert to two different IFs to get the higher gain? It's probably not a good idea to series-connect two amplifiers working at the same frequency (stability can be a practical problem)...

Hello berkeman, i make pdf file

 

[tech99]

Thank you for sending a pdf. The circuit shows an output load of 2k and this is about right for feeding a second stage. Just arrange the bias circuit so it is not short circuited by the winding. You also need an input arrangement to connect it to a mixer, and this could be the same thing again. Obviously you need to screen the coils from one another and be careful about layout to preserve stability.

 

[berkeman]

Hello berkeman, i make pdf file

Okay, so it's a pretty standard tuned CE BJT amplifier stage for 10.7MHz. You have some higher frequency signal that is mixed down to 10.7MHz, and you want more gain somewhere? Like I mentioned, just series connecting a couple high-gain stages can be problematic for stability. It's best if each IF amplification stage uses a different frequency. What is the original received frequency, and is this the only IF amp stage so far? Is the signal eventually converted down to baseband? Is the signal audio, video or digital? Can you say what the application is?

 

[berkeman]

Obviously you need to screen the coils from one another and be careful about layout to preserve stability.

Yeah, and consider a covered shield fence around each of the stages -- I've had real problems getting ganged amps at the same frequency to not oscillate...

https://e-fab.com/news/wp-content/uploads/2014/04/Shield_3D_1.jpg

 

[michael1978]

Thank you for sending a pdf. The circuit shows an output load of 2k and this is about right for feeding a second stage. Just arrange the bias circuit so it is not short circuited by the winding. You also need an input arrangement to connect it to a mixer, and this could be the same thing again. Obviously you need to screen the coils from one another and be careful about layout to preserve stability.

GoodMorning, i just have a problem, when i connect second stage, that have to be from first IF output 2K and after, do i need a capacitor only of also a resistor, and if i a need only capacitor, how much must be the value of capacitor and resistor, and output of second stage coupling? Thanks tech99...

 

[michael1978]

Okay, so it's a pretty standard tuned CE BJT amplifier stage for 10.7MHz. You have some higher frequency signal that is mixed down to 10.7MHz, and you want more gain somewhere? Like I mentioned, just series connecting a couple high-gain stages can be problematic for stability. It's best if each IF amplification stage uses a different frequency. What is the original received frequency, and is this the only IF amp stage so far? Is the signal eventually converted down to baseband? Is the signal audio, video or digital? Can you say what the application is?

Yes this the only first stage, and i want second stage, and Berkeman this for RF frequency is for fm receiver signals...

 

[tech99]

GoodMorning, i just have a problem, when i connect second stage, that have to be from first IF output 2K and after, do i need a capacitor only of also a resistor, and if i a need only capacitor, how much must be the value of capacitor and resistor, and output of second stage coupling? Thanks tech99...

I think you can get rid of R5 (2k) and connect L3 direct to C3 of the next stage.Please look at Berkeman discussion about stability; leave space to experiment.

 

[michael1978]

Yeah, and consider a covered shield fence around each of the stages -- I've had real problems getting ganged amps at the same frequency to not oscillate...

https://e-fab.com/news/wp-content/uploads/2014/04/Shield_3D_1.jpg

View attachment 232050

What is this, picture?

 

[michael1978]

I think you can get rid of R5 (2k) and connect L3 direct to C3 of the next stage.Please look at Berkeman discussion about stability; leave space to experiment.

Thank you very much sir, is working greetings.

 

[berkeman]

What is this, picture?

It is a drawing of an RF shield fence and top. They are commonly used on RF circuit boards to shield the components underneath from RF interference from other sources, and to contain RF energy being generated by the circuitry under the shield. I've used them in 2.4GHz Zigbee radio designs, for example. Here is a picture of a typical circuit board with several sections of RF circuitry that are using shields to lower cross-talk between them, and to protect against outside interference:

https://sc02.alicdn.com/kf/HTB1jeUO...tal-etching-EMI-RFI-shielding.jpg_350x350.jpg

And a picture of my PCBA with the radio section under the metal shield can:

 

[michael1978]

It is a drawing of an RF shield fence and top. They are commonly used on RF circuit boards to shield the components underneath from RF interference from other sources, and to contain RF energy being generated by the circuitry under the shield. I've used them in 2.4GHz Zigbee radio designs, for example. Here is a picture of a typical circuit board with several sections of RF circuitry that are using shields to lower cross-talk between them, and to protect against outside interference:

https://sc02.alicdn.com/kf/HTB1jeUO...tal-etching-EMI-RFI-shielding.jpg_350x350.jpg

View attachment 232121

And a picture of my PCBA with the radio section under the metal shield can:

View attachment 232120

Thanks man for explainig me, have a nice wekend