FT240-43 Torriod based on the W1JR design.

This form of choke is refered to as an Inline-Isolation Balun. Design is quite simple. 70cm of RG-142 high power coax coiled 8 times round a FT240-43 Torroid housed in a waterproof box and potted with Polyester resin. Termination is a chassis-mount SO-239 on opposite ends of the box. 

Balun is tested with full UK power limit due to power restrictions but under perfect 1:1 SWR conditions the FT-240 can handle 1KW of power.

Fully Assembled Balun £50

Parts to build your own

Torriod £9.00

70CM of RG-142 £6.00


Complete In-line Isolation Balun consists of

  • 10cm x 10cm x 5cm UV resistant Box
  • 1 x FT240-43 Torriod core
  • RG-142 high power Teflon Coax
  • 2 x SO-239 Chassis Mounted Sockets
  • All fixing hardware stainless steel
  • Potted for 100% WX proofing
 Feed at lowest band, E.G. 20m
Potted-Balun-MW0JZEClick for large image


Typical Sweep of FT240-43 Type 1:1 Balun Sweep is from 1 - 54Mhz

Typical sweep of FT240-43 type 1:1 Balun

Click for large image

All measurements taken on a MiniVNA

While every effort is made to replicate the sweep above each balun does vary slightly due to the tightness of the windings ETC.



2011. www.g3txq-hexbeam.com
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