meridio
Newbie level 2
rf power amplifier circuits hf
Hi
I need some help..Ive been trying to build a RF amplifier for 12MHZ .But ive had some problems driving power.
The basic oscillator is a colpitts one with crystal using a BJT 2N2222 .Output is taken from BJT colector.The bjt colector also has a choke tied to +Vcc.But I need to boost output power. Just 1 BJT isnt enough for getting 180Vpp and 200mA current that my circular antenna(radius=30cm) needs.
I´ve put that antenna into BJT colector in series with the choke.but i just get 26Vpp using +15 from a DC power supply .And current is really tiny...And it starts to oscillate so oddly. So I decided to leave colector and choke alone and put Antenna as a colector load out of that circuit. I dunno what to do. Finally Antenna has 0 Volt and circuit stop oscillating and i just see DC component in oscilloscope.
Ive tried a buffer ....but even a BJT buffer draws current and oscillator stop....
How can solve I this problem? ..I really need a RF power amplifier 128Vrms and 200mA. Are there any circuits or schematic can help me solve this?
Ive designed a buffer with a bjt and a power booster with mosfet (as a power amplifier) .In my SPICE simulation works perfectly. But in real PCB...it doesnt work!
Please help me
Thanks for your help
Meridio
electronicadamelltda@gmail.com
Hi
I need some help..Ive been trying to build a RF amplifier for 12MHZ .But ive had some problems driving power.
The basic oscillator is a colpitts one with crystal using a BJT 2N2222 .Output is taken from BJT colector.The bjt colector also has a choke tied to +Vcc.But I need to boost output power. Just 1 BJT isnt enough for getting 180Vpp and 200mA current that my circular antenna(radius=30cm) needs.
I´ve put that antenna into BJT colector in series with the choke.but i just get 26Vpp using +15 from a DC power supply .And current is really tiny...And it starts to oscillate so oddly. So I decided to leave colector and choke alone and put Antenna as a colector load out of that circuit. I dunno what to do. Finally Antenna has 0 Volt and circuit stop oscillating and i just see DC component in oscilloscope.
Ive tried a buffer ....but even a BJT buffer draws current and oscillator stop....
How can solve I this problem? ..I really need a RF power amplifier 128Vrms and 200mA. Are there any circuits or schematic can help me solve this?
Ive designed a buffer with a bjt and a power booster with mosfet (as a power amplifier) .In my SPICE simulation works perfectly. But in real PCB...it doesnt work!
Please help me
Thanks for your help
Meridio
electronicadamelltda@gmail.com
