Electronics > RF, Microwave, Ham Radio

Amplifying 27Mhz XTAL Oscillator

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stcoso:
Hi, I'm trying bulding a small (4-5W) RF gen from a XTAL oscillator.

I've used the following schematic to get the XTAL oscillating properly (just added a 0.7uH inductor accross C3 to get the xtal oscillating at the 3rd harmonics)  :


Obviously the output is very small (100mVpp). So i used another 2n3904 (in common emitter config, with a cap bypassing the emitter resistance). I get a nice sine wave, 1 Vrms (with a 50Ohm resistor as a load) but no real power at all.

I need something around 4W to drive a linear CB amplifier that i already have.

Searching through the internet i found a lot of schematics for small amplifier like the one i need but they use  some quiet old RF transistor wich are not so easy to find in local shops.

So..  i'm looking for some ideas that possibly involves parts easy to find.


Thank you

vk3yedotcom:
You will likely need several transistors to get it up to 5w.  Say a couple 2N2222A, then a 2N3866 or 2N4427 (to get you up to about 0.5 - 1w) then an MRF475 or similar for 5w. 

Unfortunately RF transistors are rare and are unlikely to be available from local shops. Maybe you have a junked 27 MHz CB you could pillage?

stcoso:
I just found local shop with IRF510 available.. so i'm looking for a schematic that could use these FETs instead of transistor.

T3sl4co1l:
IRF510 is quite poor at this frequency.

You're better off using ten 2N3904's in parallel!

Tim

snarkysparky:
First to get 5 watts into a 50 ohm load you will need a sinewave of magnitude.

5 =  V^2/50    or   V  =  15.8 V

So your final stage will need to be run from 25-30 Volts.

And the current magnitude will be

I^2*R = 5 W      or  I = sqrt(0.1)   =  0.316 A

I agree with Tim use several 2n3904 in parallel with individual emitter resistors.

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