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HF 4:1 Baluns
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Specifications
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These baluns were made for use with a doublet antenna. Two types, bifilar and coaxial, were investigated.
Click on a thumbnail below to see a larger picture
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The schematic. |
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Baluns were made using bifilar wound twin mains flex, . . |
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. . and with RG179B/U 75 Ohm PTFE dielectric coaxial cable. |
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It was found, by trial and error, that 7 turns was just right for best bandwidth & lowest loss. Two stacked ferrite toroids of 4C6 material are used (Philips part no. 4322 020 97201). |
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Each toroid is 36 x 23 x 15mm (D x d x h), two together are good for 400W. For further reading, see the calculation in para. 3.2.2 in the Philips application note NCO8703 in the list below. |
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The baluns are mounted in rainproof boxes for outdoor use. |
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Mounted under a gutter, for easy access from a window. |
SWR & Insertion Loss
The insertion loss of each type of balun was measured, on each band, using two identical baluns back to back.
| Band | Bifilar | Coaxial |
| 1.8 | 0.158 dB | 0.154 dB |
| 3.8 | 0.077 dB | 0.070 dB |
| 7.0 | 0.065 dB | 0.057 dB |
| 14.0 | 0.079 dB | 0.066 dB |
| 21.0 | 0.107 dB | 0.102 dB |
| 28.0 | 0.150 dB | 0.121 dB |
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SWR of the baluns from 1 to 60 MHz, terminated in 200 Ohms. Coaxial (red trace) and bifilar (blue trace). |
These measurements were made with a N2PK VNA using Exeter software.
Philips Application Notes
NCO8703: Wideband Linear Power Amplifier (1.6 - 28 MHz) for 300 W PEP with 2 MOS transistors BLF177 (pdf 165kB)
ECO6907: Design of H.F. Wideband Power Transformers (pdf 122kB)
ECO7213: Design of H.F. Wideband Power Transformers; Part II (pdf 57kB)