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     Northam, Western Australia
     QRZ Page: VK6YSF

 

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1:4 CURRENT BALUN FOR HF AND LOW VHF

1:4 Current Balun for the upper HF bands from about 10MHz to the 6m band at 50 - 54MHz.  10 December 2025. 


 

Requiring a balun to feed a balanced antenna from an un-balanced tuner or directly from a radio for the upper HF to low VHF bands, a 1:4 Guanella Current balun design using two FT140-61 ferrite toroid cores was selected. An impedance transformation balun may be required due the variations in impedances often encounter with multi-band balanced antenna system.

The Guanella Current balun is a low loss, broadband balun that will ideally choke off common mode currents entering the radio room and importantly provide a transition from the un-balanced output of the tuner to the balanced antenna.

 

Construction

 

The 1:4 current balun is derived from two 1:1 current baluns with each consisting of a close double bifilar winding of 3.5 turns wound evenly spaced around the FT140-61 Ferrite Toroid Cores. The wire is PTFE (Polytetrafluoroethylene) silver plated copper wire, of 1.0mm diameter (AWG 18), and white for this project.

Figure 4 Schematic of the 1:4 Guanella Current balun .

 

 

Figure 5 Wiring of the 1:4 Guanella Current balun.

 

Type 

Impedance transformation

Ratio

1:4

Frequency Range

8.0 ~ 60MHz

Core Used

FT140-61 Ferrite Toroid Core x 2

Number of turns

Core 1 = 4.5 turns x 2, Core 2 = 4.5 turns x 2. PTFE silver plated copper wire, 1.0mm, AWG 18, White.

SWR

1.2:1 or less. Ref: Figure ?

 

Photo 1 1:4 balun assembled.

 

1:4 balun testing 

Photo 2 Shows the Nano VNA antenna analyser plot viewing a 200ohm resistive load through the 1:4 balun. Note the 200ohm resistor appears as 50ohms due to the 1:4 balun ratio transformation resulting in an ideal SWR of 1:1. This plot shows an SWR ranging from 1.0 MHz to 60MHz with a 1.1:1 or better SWR from 10MHz to 60MHz.

 

While the core choosing is not ideal it has tested as sufficiently efficient impedance transformation at the intended power levels of 100w or less.

For Summary of suitable ferrite cores and core types for a frequency range of 100 kHz to 50 MHz for power levels of 50W, 100W, and 500W continuous and SSB. It assumes good thermal management and proper balun design. See: Power - Ferrite Core Design  

 

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Page initiated 10 January, 2025 

Page last revised 10 January, 2025

 

 

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VK6YSF JS8Call and Olivia 8/250 operations.

Current activity is generally, however not restricted to operations with JS8Call and Olivia 8/250 on the 20m and 40m band.

Proposed band and mode activity is often communicated on HamSpots: https://hamspots.net/js8/ or my profile on 

X: https://x.com/vk6ysf97230 .

Feel free to contact me to discuss or arrange a schedule for a contact.

 

VK6MJM LF (136 kHz) and MF (474 kHz) Beacon

VK6MJM is a  LF/MF station located in Manjimup, Western Australia.

Mode: Mode: FST4W 300 (Similar to WSPR)

Station details were presented by Peter Hall (VK6HP) at PerthTech 2024.Presentation PDF: Peter Hall VK6HP at PerthTech

QRZ Page: VK6MJM on QRZ.com

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Amateur Radio Station VK6YSF - Promoting amateur radio communication and experimentation.