Amp Input SWR circuitry


While testing the new amp design, I recognized that the Input SWR from 160–10M was not staying low due to the coupling of my binary pr-resistive network to the amplifier input. I want to utilize the binary pi-resistive network so that the amp and various drive sources may be matched up. The binary pi-resistive network provides 1–15 dB in 1dB steps. It is controlled by a dip switch on the board. My problem was with 1dB attenuation the input SWR was not constant from 160–10M. I tried a lot of different solutions and finally came up with what I think is a good one. The current amp schematic in pdf form is attached.  File Attachment: MOSFET AMP MODULE HFSPP V3.pdf (28 KB)

The solution I came up with is to use a 1:1 current balun using a 202–61 binocular core with #24 enamel wire. You can see the wiring of the core. The wire loops through a hole 3 turns. It is configured as a 1:1 current balun.

Balun1 hfspp3

Balun hfspp3pix

I invite any discussion about my impedance matching solution for this MOSFET type amplifier. The way the circuitry is laid out, I can have a isolated balanced input or have a low side common ground. I don’t find much literature or discussion about this sort of thing. My worse case test was on 10M with 1dB pi-resistive network. I measured 1.2:1. Other than that it was pretty much 1:1.

IF I can put this part of the circuit to bed, I can move on with power testing. I just wanted you to know that I am making progress and happy with this advancement.

73, K5OOR –  Virgil




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