rf transistor matching

[salviador]

I have any low power transistor work in vhf , I polarized DC for an optimal working point.
My question , If I do not know s-parameters of transistor, how can I build matching network in Input and output?
If I connect Bi-Directional Coupler and connect reflect channel in oscilloscope and forward in second channel oscilloscope and  with network L/C tuning for see in oscilloscope low reflection and maximun forward, is correct?

[John_BS]

Yes, what you've said is basically correct. It is difficult to give very specific advice regarding the amplifier, as we don't know how you are using it: I'm assuming it's class A?

Points to watch:

1. If you change the output loading /match, it will reflect back into the input match, so either make sure you're happy with the output before matching the input, or perform the matching iteratively.   
2. The coupler should ideally have a directivity spec better than the match you wish to acheive, say by 10dB or so.
3. If you're   matching the input to obtain maximum forward gain, and are not trying to achieve a high return loss (for critical filter termination, for instance), a figure of about 12db is adequate.
4. The coupler should be fed from a good 50 ohm source; a 6 or 10dB pad on the input to the coupler is a good idea.
5. Ditto the 'scope terminations need to be close to 50 ohms to prevent standing waves on the measuring ports.  If your 'scope has significant input capacitance, 6 or 10db pads direct on the inputs will help with this.

John

[salviador]

Thank you very much John, very clear