Folded Skeleton Sleeve Antennas

Skeleton Sleeve Dipoles (4)I am always interested in trying different antenna designs, especially if they are simple to construct and provide increased functionality. While perusing some old issues of QST magazine online I found a series of articles that discuss a design called the Folded Skeleton Sleeve. The design is a unique way to build a dual-band resonant dipole or groundplane vertical. The articles appear in the May 2011, October 2011, October 2012, December 2013, and March 2015 issues of QST magazine.

I was particularly interested in this antenna design because a simple resonant dual-band antenna could be very useful for deployment at Field Day or for EMCOMM purposes. Other multi-band antenna designs exist and can perform quite well (windoms, off-center-fed dipoles, G5RVs, non resonant end feds, dipoles fed with window line, etc.), however, most of these require a wide range antenna tuner to achieve a decent SWR on multiple bands. Other designs, such as trap dipoles, can be heavy and cumbersome with multiple points of failure. The folded skeleton sleeve design exhibits non of these limitations.

Design

Folded Skeleton Sleeve AntennaThe folded skeleton sleeve at first looks like a standard folded dipole, however, the top radiator is not continuous. Two notches are cut along the top of the window line to create the parasitic element that allows for operation on the higher frequency band.

A 75M / 40M antenna should be perfect for both EMCOMM (these are the most common HF bands used for emergency communications) and Field Day. A 40M / 20M antenna is equally perfect for Field Day and the combination of the two provides a lot of operating versatility from two simple antennas that cover the three busiest Field Day bands. I also decided to construct a 40M / 30M antenna for use as a portable antenna for digital communications.

Construction

Skeleton Sleeve Dipoles (2)Skeleton Sleeve Dipoles (3)I built the antennas using 18AWG stranded copper-weld 450 Ohm window line (Wireman #553) and folded dipole insulator kits (Wireman #804) which make fantastic strain reliefs for securing the window line. I also made my own 1:1 baluns in a similar design to what I have done before, except this time I used FT-150A-K toroids and 18AWG wire which allowed me to make the baluns smaller in size while still being adequate to handle 100W. To house the baluns I used Bud Industries PN-1322-DGMB NEMA 4X enclosures. These are well made boxes and they feature convenient mounting tabs that are easily bolted to the center insulator.

75/40 Bandwidth

75 Meter Band

  • 2:1 SWR:  3.68-3.785
  • 3:1 SWR:  3.63-3.86

40 Meter Band

  • 2:1 SWR:  7.18-7.238
  • 3:1 SWR:  7.1-7.3

While the bandwidth of this antenna is not particularly wide, it is easily matched to the radio’s 50 ohm output with practically any antenna tuner.

My ham radio club used the 75/40 at our Field Day site for the duration of the event. While obviously intended for use on 75 & 40 meters, the antenna was used on the higher bands as well with the help of a wide range antenna tuner. Over the course of field day this setup resulted in over 350 CW contacts.

40/30 Bandwidth

40 Meter Band

  • 2:1 SWR:  7.158-7.33
  • 3:1 SWR:  7.073-7.448

30 Meter Band

  • 2:1 SWR:  9.93-10.24

This antenna exhibits better bandwidth than the 75/40 and even reaches an SWR of 1.1:1 on 30 meters.

40/20 Bandwidth

This antenna is by far the best design of the bunch. This configuration results in an SWR of under 2:1 across the entirety of both the 40 and 20 meter bands.

Antenna Winders

Skeleton Sleeve Dipoles (5)Since ladder line can be annoying to work with since it doesn’t coil easily, I decided to build some winders from 1/2 inch PVC pipe to keep the finished antennas organized. I built a larger one for the 75/40 antenna and smaller ones for the 40/20 and 40/30 antennas. I am really pleased with how these turned out and plan to build more for use with other antennas; they are a fantastic way to avoid a tangled mess.

 

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