9:1 UnUn Project

This project was a commission on behalf of Frank M1CPD who required a long wire UnUn. Perhaps better known as a Magnetic Longwire Balun, it is an impedance transformer whose purpose is to feed a high impedance long wire from a 50ohm unbalanced coaxial input.  With  a 9:1 turns ratio, this gives approx. 450ohm output impedance for the long wire. The design is on John M0UKD’s website  http://www.m0ukd.com/Magnetic_Long_Wire_UnUn/index.php.

The toroid used was  an (Amidon) Iron Powder  T200-2 core purchased from Ebay (here). This is rated at 650W SSB and 400W 100% duty cycle (Digital modes etc.). Note that this is different to the T130-2 (150W) used in John M0UKD’s original article.

Below some photos taken during construction and some comments.

Stuff Needed (but not the feet)

Counted as one wind

Nine turns later (and the feet are still there, must remember to wear black socks)

Cable tied down and soldered (see also the schematic on the website linked above)

Mounted in the Box

And finally finished.



Derek M0DXC  (Email: m0xdc@lefars.org.uk)

[Additional words by John G8DZH 7-Nov-2011]


Ready-built balun, Unun’s. Plus IP66 enclosures, SO239 sockets, toroids etc. to make your own.  http://stores.ebay.co.uk/urbasket-eu?_trksid=p4340.l2563

Further Reading

Amateur Radio (G3TXQ) – UnUn experiments  http://www.karinya.net/g3txq/unun/

A 9:1 Balun For Your End Fed Antenna by Robert Betts N1KPR http://www.bobsamerica.com/9-1balun.html

LEFARS Newsletter No. 89. Pages 25-26. My Pet UNUN by Dick SV0XBN/9 (members only – login needed)  http://www.lefars.org.uk/lefars_website/members/newsletters/issue_89_view.pdf

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