Radiofax antenna: 9:1 longwire balun – DIY

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Radiofax, described in an earlier post, can be received by use of dedicated devices or a home made system. Such system would consist of a SSB radio, laptop with appropriate software and an antenna.
The key element of such kit is the SSB radio. This may be, for example, a portable radio Sony ICF 7600. Unfortunately its built-in antenna does not allow clear reception of the weather fax signal. That problem can be solved by a home made longwire antenna.

Making own longwire antenna with balun 9:1 impedance transformer is not particularly demanding.
The basic components set may look like this:

– Toroid iron powder core T130-2 manufactured by Amidon
– About two meters of enamelled copper wire ø 1-1.2 mm
– Coaxial cable – impedance 50 ohm (RG-58)
– Plug PL259
– Socket SO239
– 3.5 mm jack plug mono
– Approx. 10 meters of insulated wire
– electrical box
– Two banana sockets and plugs

Antenna connectors PL259 and SO239 can be replaced with a BNC connector and the banana connector by any other type. The toroid core can be recovered from the old power adapter.

Three sections of the copper wire, approximately 65 cm long each, were wound 9 times around the core.

Next the wire was cut to the correct length and enamel was removed from the endings. Soldered connections were made as in the images below.

The coil was then inserted in the box.

The last bit was to attach the connectors to the coated wire and the coaxial cable.

The set looks like below.


Some more information can be found here: