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Baluns were made using bifilar wound twin mains flex, . .
. . and with RG179B/U 75 Ohm PTFE dielectric coaxial cable.
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).
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.
The baluns are mounted in rainproof boxes for outdoor use.
Mounted under a gutter, for easy access from a window.
|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|
SWR of the baluns from 1 to 60 MHz, terminated in 200 Ohms. Coaxial (red trace) and bifilar (blue trace).