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.
Derek M0DXC (Email: firstname.lastname@example.org)
[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
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