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Terrestrial Broadcasting
Terrestrial Television, Digital and Analogue
My own construction, 23dB gain, motorized aerial
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<blockquote data-quote="battenfan" data-source="post: 865290" data-attributes="member: 239108"><p>I'm guessing my antenna is closer to 75 than 300 ohm so I went for a simple 1:1 choke balun. I've tried an ugly coax coil in the past but I wasn't happy with how it behaved. The bifilar is from a flat-cable off a scraped computer. From the top of my head, the distance between the leads and the dielectric constant of the insulation makes its characteristic impedance close to 75 ohm. The coil's impedance at the lowest frequency should be >5 times higher than the antenna's. An one-layered air coil has its highest inductance when the length is 2-2.5 times larger the diameter.</p><p></p><p></p><p>I've probably overdone the number of wraps. I could have spaced them further apart. Nevertheless, at less than 2 meters off the ground pointing into trees in the rain, it has great reception at least up to channel 48, maybe 50 km from the transmitter of unknown power. Maybe I was just lucky. So many unknowns.</p><p></p><p>(Oh btw, 13MB pdf, but great read: _<a href="http://www.nonstopsystems.com/radio/balun-sevick.pdf" target="_blank">http://www.nonstopsystems.com/radio/balun-sevick.pdf</a> )</p></blockquote><p></p>
[QUOTE="battenfan, post: 865290, member: 239108"] I'm guessing my antenna is closer to 75 than 300 ohm so I went for a simple 1:1 choke balun. I've tried an ugly coax coil in the past but I wasn't happy with how it behaved. The bifilar is from a flat-cable off a scraped computer. From the top of my head, the distance between the leads and the dielectric constant of the insulation makes its characteristic impedance close to 75 ohm. The coil's impedance at the lowest frequency should be >5 times higher than the antenna's. An one-layered air coil has its highest inductance when the length is 2-2.5 times larger the diameter. I've probably overdone the number of wraps. I could have spaced them further apart. Nevertheless, at less than 2 meters off the ground pointing into trees in the rain, it has great reception at least up to channel 48, maybe 50 km from the transmitter of unknown power. Maybe I was just lucky. So many unknowns. (Oh btw, 13MB pdf, but great read: _[url]http://www.nonstopsystems.com/radio/balun-sevick.pdf[/url] ) [/QUOTE]
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Terrestrial Broadcasting
Terrestrial Television, Digital and Analogue
My own construction, 23dB gain, motorized aerial
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