N2FFL's "Miracle Whip"

In my desire to setup a portable HF/VHF station I have built a battery power supply and have been experimenting with compact portable HF homebrew antennas.

This is my version of the "Miracle Whip" for portable HF operation. The original antenna can be seen in the July 2001 issue of QST , page 32. I'm not go into great detail about the construction of the antenna here so I recommend that you read the article in QST. ARRL members can view the article online here.

Musings on the Miracle Whip design an "easier to build" version from G4FON. He has two loop designs and other things also which are worth a look here.

The antenna described in QST was designed to attach to the antenna connector on the rear of the Yaesu FT-817. The Icom IC-706 has two connectors (one for HF & one for VHF/UHF) on the rear and I want to have access to both when the "Miracle Whip" is being used. I've built the antenna so it will sit on a tabletop. The whip is a Radio Shack 270-1408B 6 section telescoping antenna which extends to 72" (the antenna is 14" collapsed, two of these could be used to construct a collapsible 6/2 meter dipole for portable operation). I've installed a PL259 on the end of the whip so it can be removed for transport and storage.

The variable inductor I've constructed is electrically the same as the one in the article with some slight physical differences.

The completed antenna...

The schematic...

The Whip...

Click on an image for a lager view.

LEFT: the base of the whip before modification. CENTER: After modification. The "tab" on the end has been cut off & a hole drilled to accept a 12 ga solid copper wire (soldered in place). A small piece of 1/4" ID vinyl tubing (not rubber hose as some is conductive) has been slid over the outside of the antenna, this acts as an insulator and a bushing. RIGHT: Finished! A PL-259 has been screwed on over the vinyl tubing. The copper wire was then soldered to the center pin of the connector.

The Variable Inductor...

LEFT: The rheostat before disassembly, it's alot smaller than I had expected. CENTER: The toroid, it has had 64 turns of 26 ga enameled wire evenly wound on it. RIGHT: The completed variable inductor.

In the QST article it is stated that the antenna will tune and function on 80 - 2 meters. This is not the case with mine. I've tried varying the length of the whip to no avail (the article calls for a 48" whip). Unless otherwise noted the whip is fully extended. On 80 meters the SWR is 4 to 1, ouch, I get a better match on 160 where the SWR is 2.5 to 1. On 40 meters the match is much better, with an SWR < 1.75 to 1 across the entire band. 20 meters is even better, with an SWR < 1.5 to 1 across the entire band (if I'm careful I can get it down to 1.1 to 1). On 17 meters I have to fully collapse one section of the whip then the SWR can be brought down to < 1.5 to 1. On 15 meters the SWR can only be brought down to 2.5 to 1 (the wiper is at he end of the windings) and RF feedback into the radio starts to become a problem. Using the antenna on 12, 10 & 6 meters is not an option as the SWR is very high. I'm going to have to do some experimentation & see if I can bring the SWR down on those bands.

I would have to say yes. After testing I went on to 20 meters and tuned the antenna. With everything set up on the basement floor I was hearing quite a few strong signals (20 - 40 dB over S9). I then worked a station in New Hampshire and received a 59 signal report, not bad considering I'm in New Jersey and was only running 20 watts.