Another HF Loop Design


WA8LMF
 

The "Kite Loop" antenna was published in the July 2019 issue of QST, page 39.   This is a "skinny" loop, predominately vertical physically that radiates a horizontal polarized signal.  The original design consisted of 75 feet (23 m) of wire slung over a 30-foot (9 m)  telescoping mast and fed at the bottom with a tuner.   About a third of the way down from the top, the wires on both sides are pulled outward with guy wires or rope to form a kite-shaped loop.   The author built and modeled it for 20 through 6 meters.  By virtue of being fed at the center bottom of the loop, it is horizontally polarized, despite being a predominately vertically-shaped stricture.  It definitely does NOT depend on a ground plane or radial system,

Two days before a ham fest last weekend, I decided to build a variant of this thing.  I have a modified 50-year-old tent-camper trailer with a bracket for a 40-foot ( 12 m) telescoping German  "SpiderBeam" mast mounted on it.  Instead of pulling the sides of the kite outward with guys, I decided to push them outward with  1/2" PVC water pipe spreaders mounted to the mast with a plastic pipe "cross" fitting. The spreaders extend about 7 feet (2.1 m) to either side.  This makes the antenna setup self-supporting  I grabbed  72 feet (22 m) of AWG 12-gauge solid-copper insulated house wire and threaded it through holes drilled at the end of the pipe spreaders.  The bottom of the two wires were pulled back together and connected to the HOT and GND terminals of an Icom AH-4 tuner resting on the top deck of the trailer at the bottom of the mast.  The result is shown below. This is a crude cell cam shot taken just before rain broke up the hamfest.   I intend to get a better shot and then mark up the wires in an image editor so they show better,  at another ham fest this weekend. 

The light-weight all-aluminum trailer is towed effortlessly  by my Jetta TDI.  The Spiderbeam mast telescopes down to less than 4 feet (1.2 m) but can erected to full height in less than 4 minutes.   I have used this platform for all manner of HF and VHF/UHF portable antennas for Field Day, hamfests, radio club demos, etc and call it my "Porta-Site".   In the shot above, you can see the AH-4 auto-tuner resting on top of a yellow plastic bucket.    Normally the AH-4 is a single-ended tuner for random wires working against ground.  

I have made the whole tuner float above ground by wrapping multiple turns of both the control cable and the coax feed line through large ferrite cores and then placing the tuner body on an insulator (the kitty litter bucket).  This makes the AH-4 effectively a balanced-output device with both terminals ("ANT" and "GND") floating above ground.  I have used this technique at home for years to feed a  ladder-line-fed  balanced horizontal dipole with both an AH-2 and an AH-4. 

The ham fest outing last Sunday was the "maiden voyage" for this setup. It worked perfectly!    The author of the original Kite Loop article only used it on 20 through 6 meters.  Using a Yaesu FT-857 to drive the AH-4 and loop, I found it tuned effortlessly on 30, 40, 60 and 75/80 meters as well.  It not only tuned easily; it actually seems to be quite efficient. 

Spinning across WWV on 2.5, 5, 10 and 15 MHz (I have all the WWV freqs stored in adjacent memory channel slots on all my radios for quick propagation checks), I was astonished to hear WWV booming in on all the freqs above at S9+ around 10 AM local (US Eastern Time).   From my location in Michigan, the WWV transmitters are about 1000 miles (1600 km) away to the west in Colorado - normally I only hear the 2.5 and 5 MHz signals at night.    A ham buddy of mine made some contacts on 75 meters with a informal rag chew group he frequents on 3684 KHz with my lashup.  He was astonished at the solid signals over 200-mile-plus paths on 80m at  10 AM local time.

For casual setups at ham fests, this antenna is a vast improvement over either traditional verticals (never a decent ground plane in a temp setup, and incessant RFI/EMI issues).   Or the horizontal ladder-line dipole I would fan out from the top of the mast (downward sloping wires interfering with other people' spaces at the event).  The vertical loop fits entirely within my own space. 

The main problem is that the solid house wire is a pain to coil up and store -- it's just too stiff.   The next generation of this thing is going to use Wireman "Silky" poly-ethylene-jacketed 18-guage stranded copperweld wire.   I've used this stuff before and it's very managable for deploying and coiling up temporary antennas.



Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
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Home Page:          http://wa8lmf.net

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Chris Moulding
 

It looks very similar to the skeleton slot antenna design.

A vertical slot in a metal sheet radiates horizontal polarised radiation due to the RF current flowing around the edge of the slot.

A skeleton slot effectively removes the metal sheet leaving the edges of the slot.

In the UK this was originally used for 8 over 8 element TV and amateur 2m antennas by J-Beam. A very effective antenna back in the day!

Regards,

Chris