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End Fed Half Wave Experiment – Part 3

By w4kaz, created on 2021.03.17 at 08:22:00 | last changed on 2021.05.06 at 22:33:20 |

 End Fed Half Wave Experiment – Part 1, End Fed Half Wave Experiment – Part 2 The “Tune-up-ening”

The first attempts to tune up the real antenna did not go well. I found from the trap dipole project attaching the wires beyond the trap was needed to get the higher bands tuned properly. This worked against me here. With the high impedance on the end fed I was better off tuning the 40m antenna segment without the coil and 80m tail attached. Unfortunately, I wasted a lot of time experimenting/snipping before I decided to detach the inner antenna from the coil.

Once taking that step, I found I had probably trimmed too much off. Tuning for 40m without the coil proved simple enough. After that the other bands were easier too. I was also able to re-attach the coil and 80m tail, and find tap settings and tail lengths to allow operation with good matches on 80m and 20m. With the 20m tails attached 40m operation on the upper edge is possible. With tails 40m SWR was a bit high on CW segment, although possible with a tuner. 10m seemed unaffected by the coil and tail. 15m provided low SWR only with the coil and tail detached, but SWR of 2:1 up to 3:1 with 80m coil and tail.

Antenna Stuff

The coil as wound measured out to 77.5uh, resonant at 3.85Mhz with 22pf of capacitance. It is ~63 close-wound turns on a mystery plastic coil form of […]

Continue reading End Fed Half Wave Experiment – Part 3

last changed on 2021.05.06 at 22:33:20 | Category: Antennas, Curiosities | Leave a comment

End Fed Half Wave Experiment – Part 2

By w4kaz, created on 2021.03.11 at 06:26:00 | last changed on 2021.05.06 at 22:33:03 |

End Fed Half Wave Experiment – Part 1

Construction

The Initial cut of the antenna and the completed feedpoint enclosure.

Having looked at many of the articles available on the WWW, I wound up favoring the design well documented by G0KYA, Steve Nichols.  When modeling the antenna I started out using a coil value of 67.5uh.  Then I ran the model using the appropriate value of impedance at each given frequency.  The coil as shown above is about 63 turns of 16ga solid insulated wire on a plastic coil form of just over 2 inch diameter.  That was right at the limit of the amount of wire I could lay down on the available form.  The completed coil resonated with a handy 22pf capacitor at 3.855Mhz, which calculates out to an actual inductance of close to 77.5uh.  With the coil value known, I re-ran the model to tweak the initial guestimates with actual values of XL for the model’s load.    Then cut wire for the 40m leg as well as the 80m tag end.  BEFORE tuning wire lengths are long, 71 feet and 15 feet(about 21.6 meters and 4.5 meters). 

Inductor

77.5uh inductor, ~63 turns of 16ga insulated wire wound on a 2 inch plastic form.

The coil form used seems better for RF than PVC pipe, and is a one-off that happened to be in the parts bin, original source un-remembered.  I gave it a run in the microwave, and it showed little […]

Continue reading End Fed Half Wave Experiment – Part 2

last changed on 2021.05.06 at 22:33:03 | Category: Antennas, Curiosities | Leave a comment

End Fed Half Wave-Experiment du’Jour : Part 1

By w4kaz, created on 2021.03.08 at 15:53:33 | last changed on 2021.03.12 at 22:12:18 |

Just about the only wire antenna in common use I had not experimented with is the End Fed Half Wave(EFHW). So WTF. May as well give it a go.Â

2021 planning had me booking a stay on Cape Lookout National Seashore(CALO) for the end of June rather than the end of July. I tried unsuccessfully to make the reservation in 2020, but could not. Success for 2021. So my FD 2021 will be from Cape Lookout.Â

Given the layout of the cabin I prefer at CALO campground I decided to tinker with the EFHW as a possible solution for allowing multi bands with least effort. The “least effort” factor is growing more important with each passing year. But the EFHW itself piqued my curiosity as well, and it seems it my provide a solution to the “least effort” vs. “works well” conundrum.  Â

So, here lies the experimental portion.  NUMEROUS versions of the classic 49:1 transformer are documented on WWW and in the now ubiquitous scrootoobe video. Version guidelines exist for either 80m or 40m multi band versions. Quite typically I chucked some of that and decided to re-invent the wheel – because what is the fun of experimenting if you are just going to follow the cookbook? Wellll…..not quite that either.

Where to start

Looking for a 40m size and decided to try modeling out a 40m EFHW fit out with a loading coil and tag end to allow 80m or 75m. The […]

Continue reading End Fed Half Wave-Experiment du’Jour : Part 1

last changed on 2021.03.12 at 22:12:18 | Tags: , , | Category: Antennas, Curiosities, Homebrew, Shack Project | Leave a comment