ADVENTURES WITH  ANTENNAS
PT.1

(Leading down the path to an MLA)

Living in an apartment or a house with NAZI-Like HOA's can be frustrating to the modern Ham, in fact, the apartment we lived at 10 years ago was so much easier to rig up an antenna system compared to where we are now.

I have tried indoor dipoles, no-ground ham sticks, and even the MP1 "Super" Antenna with nary a success during the course of several years. My sanity has been preserved by either ignoring HF altogether, selling off my equipment, or using indoor wires near a window for listening purposes only.

For several reasons it became clear to me that this year it would be time to put-up or shutdown, with the latter not truly being an option. "But what could I do successfully" I asked myself, especially with our current Sunspot cycle in the doldrums'?

The hunt for a solution had begun!

[disclaimer - I am definitely NOT an expert in antennas. Anything you read here should be double-checked via web sources. I'm throwing out information that I've picked up from reading, surfing, and watching videos, so I may err unintentionally, 'Nuff Said]

One likely candidate presented itself in the form of an end fed half-wave wire (EFHW). These antennas are basically a wire, precut to a certain length, attached to an UnUn as opposed to a Balun, fed with at least 22 feet of coaxial feedline plugged into a antenna tuner by the transceiver.

FIGURE A

There is plenty of information about the specific lengths you can choose to get easy-to-tune low SWR, but for my purposes that length was going to be 33.3ft. The UnUn (Unbalanced-to-Unbalanced) would typically be either a 4:1 or 9:1 ratio, with 9:1 being the current favorite for builders of their EFHW antennas.

The >22ft. length of coaxial feedline would actually be acting as a counterpoise, negating the absolute need for an Earth ground. Just GOOGLE UnUn and/or EFHW antennas and you'll find a butt load of information. Do the same on YouTube and then be prepared to spend hours upon hours watching different operators testing a variety of homemade or OEM designs.

Figure A shows the basic, simple idea behind the EFHW antenna. You take a 1/2 wave length of wire (in my case - 33.3') connected to the "Impedance Transformer" i.e. - a 9:1 UnUn, which has 22 ft. or more of coaxial feedline, running to your rig and external antenna tuner.

FIGURE B

On EBAY, you'll find a variety of "Mystery" boxes similar to the one in FIGURE B.

There are several exterior connections. These are:

1. An SO-239 (bottom)

2. Connection for the length of wire

3. And, a connection for your ground / counterpoise




Assembled UnUn's are usually priced from around $40 to as high as $100. So what is the secret Mojo inside?



FIGURE C

By looking at FIGURE C, you can see that it's nothing more than a circular ferrite core with groupings of 3 wires wrapped on 4 turns around and through the ferrite core.

Ferrite cores are something you've seen before, and can be found in many different electronic designs -

Computer power supplies / motherboards, etc.

With one difference: The particular material used to make up a ferrite core is specifically matched for RF / HF situations.

One wire connects to the center pin of the SO239, another to the SO239 ground, yet another to where your half-wave wire will attach, and finally to the lug where a ground / counterpoise will be attached, should you use one (that's the tricky part - not using a ground-counterpoise).

FIGURE D

A diagram of what you see in Figure C is viewed on Figure D.

There is no magic.

As well, typical results will vary from "GREAT" to "Argh" I wasted my money





I had issues using one inside on the 2nd floor without the counterpoise. Outdoors, running QRP with my FT-817ND I had good results, and better results when I utilized a counterpoise. I bought the least expensive UnUn with antenna wire off Ebay for about $39. I was lazy and did not feel like scrounging around for one part or the other so I picked the least expensive-yet-well-regarded setup and suggest that, in lieu of building one, do the same thing. During November-March I might be tempted to use one at the local park, but the SE Texas heat is not my friend. 

For some excellent information on end fed antennas you could google or simply check out AA5TB's website!


Is the end fed good for an indoor antenna? I can only speak for myself and in my situation - No.  My antenna wire was 33' however, if you had the space, a longer wire with a counterpoise might be doable. But, that's a lot of wire strung around your QTH.

MAGNETIC LOOP ANTENNAS

When it comes to antennas, as a rule, there is NO magic. As a rule. The closest thing to "Magic" is the Magnetic Loop Antenna, or, MLA. Most of the commercial MLA's under $500 with the exception of the MFJ model,are built for QRP communications, usually under 25 watts. These QRP MLA's are very portable and break down into a small canvas carrying bag very easily. They are great for taking your station off-the-grid.

Most MLA's can be used horizontal or vertical and all of them have common traits like: 

1. Being very narrow-banded, requiring constant tuning if you change your operating frequecy more that 15Khz.
2. VERY directional when used as a vertical.
3. Quiet. Because of the narrow bandwidth the MLA will let you minimize electrical noise as well as helping with adjacent channel rejection.

In PART 2 of my article (Aug-Sept) I will go into more detail about MLA's and the benefits or drawbacks of using one.

And now... A look at the weather:

   

73,

Woody