RX antenna - K9AY loops switch with FIXED Rload

Current version 3.1 (last rev 2.2.2019)(Edit)

Quick Start Guide

Assembling KIT(Edit)

All parts you need - KIT(Edit)

The drill drawing(Edit)

Paste the drawing on the box and fix it with some tape.

Schematic diagram(Edit)

- version 3.1

Insert rest parts(Edit)

- small yellow Caps 104 = 100nF 3x

- yellow small polyester capacitor 104 1x

- bigger yellow PTC - EX10 1x

- black inductor 1x

- two blue Varistors

- two small resistors 1k

- two LEDs - pay attention to polarity! Long leg is +++

- Rload 2W resistor on the bottom side


- By the jumper JP3 you can select 50 or 75 Ohm coax output

- Jumper JP1 must be short if you want to control direction over coax

- By the jumper JP2 you can select controlling over coax or DC voltage on connector X3

TRANSFORMERS winding - very important thing!(Edit)

    • for 50 ohm coax feed line : 2 turns on primar (coax) and 6 turns on secondar side (loop)
    • for 75 ohm coax feed line : 2 turns on primar (coax) and 5 turns on secondar side (loop)

- In version 2.3 and higher, you can select Coax impedance by jumper JP3.

- Transformer should have 5 + 1 turns.

Common-mode coax choke(Edit)

- choke measurements

Wind the coax(Edit)

  • Common mode current choke construction
  • Wind 4 turns on one side than cross to another side of cores and wind rest turns.

Solder the coax (Edit)

KIT - all parts assembled.(Edit)

- sri photo of older PCB version

Example of controller(Edit)

- Injector to coax line:

- direction controller

K9AY loops design example.(Edit)