[Antennas] balun question

[David Kelley]

>I have a Van Gordon 4:1 balun that I use on my
>homebrew G5RV antenna.  It goes between the 300 ohm
>twinlead and the 75 ohm coax.  While doing some
>checking on my different coax runs this weekend,
>noticed that the coax for the G5RV is shorted between
>the center pin and the braid.  Traced the short back
>to the balun.  Is this normal for a 4:1 balun-to have
>the center pin and outside connector shorted, or did
>mine go bad.  Any feedback is appreciated.
>
>73s John NE0P

John,

If the balun is a trifilar-wound (3-wire) type, then yes,
there could be a DC short between the braid and the
center conductor.  Many of the 4:1 designs have the
"bottom" end of one winding connected to the "top"
end of another, so there would definitely be a DC
short.  Any edition of the ARRL Handbook or Antenna
Handbook should have a discussion of baluns in it.
If you look at the circuit diagrams, you'll see
immediately why there's a DC short.

73,
Dave

--
Dave Kelley, NB4J
State College, PA
Centre County