Suggestions on how to build a good power amplifier

Status
Not open for further replies.

Abu Ammora

Full Member level 2
Joined
Jun 13, 2005
Messages
135
Helped
5
Reputation
10
Reaction score
2
Trophy points
1,298
Location
East Coast
Activity points
2,480
bfg97 amplifier

My FSK TX Circuit need power Amplifier , I tried to make Class C tuned Amplifier "Trasistor used 2N2222A" but i failed to tune the freq. Practically after implementing the Ct on PCB , So have anyone any suggestions to how build GOOD Power Amplifier , My Goal is 100 meter RF Link ?
 

bfg97 as amplifier

What Frequency are you using?
What power do you want at 100 meters?
What is your DC rails?

I would google your requirements.
 

Re: Power Amplifier

- Frequency is 90 MHZ

- About transmitted power i can't Determine it , as i know Pt=Pr+losss , and i don't know how to start and calculate the losses , But the targetted distance is 100 meter?

Dc rails is 9V
 

Re: Power Amplifier

Why No one replied , Is my Question Containing Some technical mistakes needed to be corrected or re-specified ?
 

Re: Power Amplifier

Friend. Its simply to easy to do and you should first look with Google.

If you want to know. do't try class C won't work. use a coil of 100nH from your collector to a resistor of 120 E to VCC and a resistor from 120E resistor/100nH point to base of 1.8 K. connect the Emitter to ground. input capacitors are 1 nF to base. and output capacitor is 180pF from collector to load(antenna).

This will give you some 20 dB gain with a BFG97 @ 100 Mhz.

regards,

Paul.
 

Re: Power Amplifier

Thanks Paul , But I want u tell me that the Circuit shown is the one you meant (Plz reply me yes/No)

And i want to ask about why the components take the exact values you posted , Can u give me short Description of them ?

Can you give me alternatives for BFG97 ? What about 2N2222A ?
 

Re: Power Amplifier

Hi, If I remember correctly it is the circuit i designed some years ago including the values for 100MHz. You can try a 2N2222A but this will not give the same gain. regards, Paul.
 

    Abu Ammora

    Points: 2
    Helpful Answer Positive Rating
Re: Power Amplifier

Allright Paul , i simulated your Ct and here's the results , but i think that the o/p contain only +ve half cycles Why? or is it enough ? Is In FM transmission We don't care for -ve cycles ?

i Watched also its spectrum , and i find Freq. component exist @ 100Mhz as you told exactly ..
 

Re: Power Amplifier

Hi, I made an error. 120 Ohm should be 56 Ohm !!.. And use a 50 Ohm load in your simpulation please !!.. Load should be placed from 180pF output capacitor to ground !!.

regards,

Paul.
 

Re: Power Amplifier

I made it and here's the results , Same problem , Paul
 

Re: Power Amplifier

Hi, What are you doing friend. You put 1 Volt into the amp and what do you expect 20 Volts or more output on a 9 volt battery ???.. you should lower the input power (voltage) or increase the power supply but you can't expect an 10 - 15 dB amplifier to feel happy with 1 volt input at 9 volt battery.

1 Volt input = 20mW or 13 dBm. This alone is already more than you need for 200ft.
Lower you input to 0.3 volt = 2.55 dBm or 1.8 mW the expected output is then some 20 - 50 mW. With a BFG97 @ 12 Volts you can expect 0.5 Watt with 7 dBm input.

Paul.
 

Re: Power Amplifier

Thanks Paul , you're right , i made the changes on simulation and it was OK , but if i know the sensitivity of my receiver , and i know the Distance and the operationg freq. how can i calculate the MIN Power req. to transmitt from TX , Do u know any practical equations or graphs to help me ?
 

Re: Power Amplifier

Hi, If your receiver's sensitivity is 10uV which is not good at all and your using a normal 1/4 L ANTENNA you should have some 100mW for your radio link (wideband FM) to get 200FT which is 60meter.

No formula's since this is something that you can't calculate since I don't know your enviroment but my knowledge is telling me this .

Paul.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…