[Elecraft] KAT 500 and open wire

[rv6amark]

Re:  "...what is the old dual air coil Heathkit B-1balun, a current or voltage type?  If I remember correctly, they are 4:1 ratio."

From the Heathkit manual:  "The Heathkit Balun Coil Set, Model B-1 is a convenient transmitter accessory which has the capability of matching unbalanced coax lines, used on most modern transmitters, to balanced lines to either 75 ohms or 300 ohms impedance".

The manual discusses its use with a dipole (~75 ohms) or a folded dipole (~300 ohms), and the analogy of using a line transmission line to get the desired impedance transformation.  It is a very short but interesting read.

The assembly manual shows how to wire it in 1:1 or 4:1 configurations.  The schematic is identical to the Elecraft BL2 , except it uses air core coils instead of ferrite coils, and there is no switch to easily change between impedance ratios.   

I have never used my BL-2, so I cannot vouch for its effectiveness.  I have often wondered if it might be compromised by the 2 bifilar wound "non-self-shielding" air core coils tightly packed into a metal enclosure resulting in enough capacitance or magnetic coupling to each other and the enclosure to reduce its effectiveness.

I do, however, open it up occasionally and admire those beautiful inductors!

Mark
KE6BB



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