(Part 3) How to Design, Build, and Test an RF Linear Amplifier (Input Board) 

RF Man, the removal of the resistor and replacement while watching the effect of the SWR.... that was very instructive. Thanks.

This is gold Sir.

Enjoyed a lot.

Again, I really appreciate this series. At one point, could you show your LT Spice simulation for IRF510 input impedance? Are you measuring the input impedance at the primary side of the input transformer? VA3GPJ

Fantastic, I'm learning a lot. Very thorough. Waiting for the next one. I am a bit confused. Question: The secondary is matched to 50 ohms, is this because the input Z of the IRF510 along with the input resistor is 50 ohms? Or are we just isolating the output of the radio from the input stage of the MOSFET and 50 ohms just happens to be the typical output Z of most radios and the MOSFET doesn't care about input ? In my mind I want to match the output of the transformer to the input Z of the MOSFET. Could you explain this please? Please correct my thinking.

Thanks for interesting and really educational information on building amplifier. I have a question on the resistor across the transformer. Would be an idea to have a variable resistor there in order to fine tune the Q?

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Are the pages you display available for download?

Can it design for 144mhz sir? Thankyou

Where did you find the formula for calculating the minimum inductance of the primary winding of the RF transformer? That formula is incorrect. The reactive resistance or reactance of the primary winding of the RF transformer at the lowest operating frequency, in this case, 10MHz, should be 5 to 10 times greater than the input impedance, which is 50 ohms in this case. An inductance of 11.2uH for the two windings is acceptable because its reactance is approximately 7 times greater than 50 ohms. You are unclear about the input impedance of the IRF510 transistors. You've placed a 60-ohm resistor in parallel with the input impedance of both transistors, thus lowering the input impedance to 50 ohms and making it somewhat variable with frequency changes. The cost of this is increased drive RF power. The concept of adapting input power from this perspective is not good because it results in increased drive power. The correct way to maintain relatively constant input impedance over the range of 1.8 to 30MHz is through properly designed negative feedback drain-gate. The whole point is for such an amplifier to operate throughout the mentioned HF range and provide approximately uniform output RF power at the output. I have more criticisms, but for now, let's stick to these.