13.56 MHz Power Amplifier Reverse Engineering Process

Thread Starter


Joined Sep 12, 2019
Hi everyone,

I'm trying to reverse engineer a power amplifier operating at 13.56 MHz whose power output is 45 W. I'd like to understand the circuit's schematic so that I can design my own amplifier with the same operating frequency, but with a scaled down power output of 17 W.

First, I started off trying to recreate the schematic on LTSpice. I ran into some issues with the layout of the schematic used in the amplifier that are described below.

*On a side note, the attachments to my LTSpice simulation as well as the amplifier's schematic are at the end*

1. T1 is a three-legged transformer that is drawn on the schematic as this symbol:

On the PCB itself, it is a toroidal core wounded with 2 copper wires than run along with each other in a parallel manner. The middle wires that are tied together, designated as a+b, represents port 2 on the symbol seen above.

I am confused as to whether this is a 1:1 transformer or an iron core inductor. On LTspice I have drawn it as a 1:1 four-legged transformer where additional output on the secondary core is grounded.

2. T3 is a 1:2 transformer that has an additional fifth leg represented by the symbol shown below:

The transformer before winding it with wires looks like this:

After winding it with wires:

In the LTSpice schematic, I replaced the third port on the transformer which originally goes to ground with the fifth port's connections. Is it fine to do so?

3. Since there is no 78L06 model on LTSpice, I have opted for the LT317A regulator instead.

4. I am unsure of what the inductance used for RFC high-frequency choke coil L1 is so I'm currently starting off at 100 uH.

When I tried running the simulation on LTSpice, I cannot get any voltage or current reading across my load resistor. Could you help guide me as to what I should be troubleshooting first?

Thank you in advance kind folks!


Thread Starter


Joined Sep 12, 2019
Hi, no this isn't coursework.

I'm just trying to better understand what each part of this amplifier I bought off AliExpress does and how it can be reconfigured to output either a higher or lower power.