[Elecraft] re:Baluns - give me a kit!

Mon Jun 3 01:36:04 2002

Baluns are not particularly difficult to make - the only problem is finding the
correct ferrite for the torroid.  As already stated there is plenty of design
information on the internet.

The balun I made to feed our open wire fed doublet in NFD this weekend uses a pair of
(I believe) FX1588 Philips torroids taped together to make a single torroid.  I
acquired these a long time ago, and believe they are now hard to come by.
Construction is as per the designs in the ARRL handbook - a trifilar winding of 10
turns of wire is used.  This is configured by means of a miniature toggle switch to
change between the 1:1 and 4:1 ratios, a single contact switch can do this.  There is
nothing magical about baluns, but it is worth noting that the common mode rejection
is better in the 1:1 case, but as this requires a trifilar winding it is probably the
reason why 4:1 is more often used.

You need enough inductance in the torroid to give correct response on the lower
bands.  If as in our case we wanted top band operation, many of the more commonly
available torroids simply don't have a high enough AL.  But once you have found the
right part, the rest of the construction is childs play.

Of course as mentioned the real use of the balun in this case of feeding tuned line
antennas is unbalanced/balanced transformation.  Whatever the impedance ratio is, the
atu will probably be able to cope.  We found it matched better in the 1:1 position
but that was probably just related to the actual impedance we had.  There is nothing
magical about these baluns, they are remarkably simple, and they certainly do the job
they intended.

73s Dave G3YMC
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http://www.dsergeant.btinternet.co.uk