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Sec 9.5: Baluns for Yagi, Quad and Rhombic Antennas

By Jerry Sevick
From Transmission Line Transformers, Fourth Edition

Sec 9.5: Baluns for Yagi, Quad and Rhombic Antennas

To date, the most popular balun for antenna use has been the 1:1 (50:50- ?, nominally) trifilar design by Ruthroff. It has been used successfully in matching 50- ? coax to Yagi beams after shunt-fed methods were employed in order to raise the input impedance. It has also found success in matching 50- ? coax directly to 1/2- ? dipoles at heights of 0.15 to 0.2 ?, where the resonant impedances are 50 to 70 ?, respectively (the resonant impedance reaches a peak of about 98 ? at a height of 0.34 ?). Outside of these two cases, baluns have found very little use in matching 50- ? coaxial cable to resonant impedances far removed from the "nominal" 50 ?. For the experimentalists, baluns for the following antennas are offered.

Sec 9.5.1: Yagi Beams

Sec 9.3 and Sec 9.4 described Guanella baluns with ratios of 1:4 and 1:9 which can match 50- ? coax directly to Yagi beams with balanced and floating impedances of about 9 to 15 ? and 5 to 8 ?, respectively. Fig 9-18 shows a photograph of two other baluns capable of matching 50- ? coax directly to higher-impedance Yagi antennas. On the left in Fig 9-18 is a balun designed to match 50- ? coax to a balanced (and floating) impedance of about 20 ?. Its useful impedance range is...

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Antennas
Antennas are structures or devices used to collect or radiate electromagnetic waves.
Impedance Matching Networks
Impedance matching networks are electrical circuits which, when connected between two networks, match the output impedance of the source (the first network) to the input impedance of the load (the receiving or second network). The purpose of matching these two impedances is to minimize wave reflection and/or to maximize the transfer of power between the system and the load.
Transformers
Transformers are electrical devices that are designed to transfer energy from one circuit to another by electromagnetic induction. They are used typically to increase or decrease voltage as it passes from one side of the device through the other.
Signal Transformers
Signal transformers transfer information from one circuit to another by electromagnetic induction. They are used to increase or decrease the voltage from one side of a power transformer to the other.
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