Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Suggestions on how to build a good power amplifier

Status
Not open for further replies.
Abu Ammora

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

    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

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top