[VHFcontesting] tuning a 6M plumbers delight dipole fed with a current balun

[Steve Kavanagh]

Mike

What you see is normal, I think.  There are a few factors at work:

(1) Yes, the balun pigtail length is important (and the size of wire/strapping used will make some difference, too).  I'd probably start with the overall tip-to-tip length of the dipole and add any excess length of the balun pigtails to come up with an equivalent length number.

(2) The 234/f rule of thumb is really intended for HF wire dipoles ( think), where the ratio of length to diameter is a huge number.  On 40 m a 14 gauge wire dipole has a length-to-diameter ratio of about 11,000, for example.  The resonant frequency is lower than the rule of thumb tells you (or the resonant length is shorter for a given frequency) for antennas with a smaller ratio of length to diameter ratio (which is about 220 in your case).

(3) It is possible (but definitely not certain) that the balun itself is introducing some inductive reactance in series with the impedance seen at the centre of the dipole.  That would move the resonant frequency down a bit more.  This would not be surprising since the balun is operating near the edge of its design frequency range.

You should be able to just tune it to frequency and enjoy.  In theory the impedance should be a little higher than 50 ohms at resonance but it should be close enough for your rig to be happy with the SWR.

73,
Steve VE3SMA