First step in building a Field Day dipole

2 May

Here’s a 1:1 current balun I wound for the folded ‘skeleton sleeve’ 40m/20m dipole antenna that we’re building for our second Field Day antenna:

1:1 current balun: 10 bifilar wound turns of 18 AWG magnet wire covered in 16 AWG PTFE insulation, wound onto an Amidon FT-150A-K toroid. This will comfortably handle 100 Watts at Field Day.

It may not look a big deal, but it actually is. Its functions in life are two-fold:

  1. to ‘choke’ off common mode currents flowing on the outside of the coax feed line braid that could enter the shack (bad news)
  2. provide a transition from the BALanced antenna to the UNbalanced coax feed line (good news)

Here’s what it looks like housed in its plastic box:

The plate to the right is specially designed to accommodate 450 ohm ladder line with full strain relief. In this antenna, the ladder line is the antenna, not the feed line. Coax is attached to the SO-239 socket at the left and fed back to the operating position.

Want to learn more about the skeleton dipole and baluns? Of course you do:

Folded Skeleton Sleeve Antennas

Simple explanation of balun theory and construction:
http://vk6ysf.com/balun_guanella_current_1-1.htm

And if you’re really, really interested in balun theory, here’s the definitive guide from W7EL:
https://eznec.com/Amateur/Articles/Baluns.pdf

Don’t forget: Tuesday, May 16 at 7pm, Red Cross House.
I’ll be talking all about Field Day with slides and demonstrations at the WARA May meeting. If you’re coming along to Field Day (you are, right?), I would strongly recommend you attend.

73. Steve, VA7KH

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