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Showing posts from August, 2013

A 5/8 wavelength vertical for 10 meters. Post #224

How would you like to build a 10 meter vertical with some gain and a lower radiation angle than the usual quarterwave vertical?  You can realize this goal by building and using a 5/8 wavelength vertical antenna on the popular 10 meter amateur radio band.

If you use 50-ohm coaxial cable as your feed line, you'll need a matching device at the base of the antenna to make the antenna work correctly.  However, you can simplify the matching problem by using 450-ohm ladder line, a 4:1 balun, and a short piece of 50-ohm coaxial cable connected to the antenna terminal of your antenna transmatch.  The 5/8 wavelength vertical also requires a ground radial system to realize its full potential.  The radial system needn't be an extensive affair buried in the ground.  I used six elevated 5/8 wavelength radials for my antenna.  Thanks to the ladder line, the 5/8 wavelength vertical also is usable on 20 and 15 meters.

Faced with a more complicated construction project than the usual quarterwa…

The Bent Dipole or Inverted "U" antenna. Post #223

Have you ever wanted to erect a full half wave dipole antenna for your favorite amateur radio band, but just didn't have enough horizontal space to put the antenna?  This could be a problem for 80 and 40 meter dipoles, which can stretch out to 135 feet/41.15 meters (80 meters) and to 67 feet/20.42 meters (40 meters).

According to an article by Claude Jollet (VE2DPE), most of the rf radiated and received by a dipole is concentrated "in the middle 60% or so of the antenna...the ends can be dropped down from the horizontal without much adverse effect."

That was great news to me, since my back yard has a maximum length of 50 feet/15.24 meters bordering the rear of my house.  So, if I bent the horizontal dipole at the 60% part of the flat top and let the remaining length hang down well above ground, I should still retain most of the dipoles good qualities.

I decided to erect a quickly built bent or inverted "U" dipole to see what results I could get.

MATERIALS:

Usi…

A Full Wavelength Loop for 40 through 10 Meters. Post #222

Having built a series of verticals, inverted vees, half squares, and loops for my amateur radio activities, I decided to "thin the heard" of my less than successful antenna efforts and concentrate on a few antennas that have given me the most contacts and overall satisfaction.

Although I love the ease of assembly and portability of homebrew vertical antennas, I just don't enjoy the labor involved in putting in a ground radial system.  The elevated counterpoise systems I've used have been less labor intensive than the buried radial approach, but, still, there is a lot of wire running around my property which is a safety hazard for children and pets.

The inverted vee antennas are being kept for portable and emergency use.  I have a few telescoping fiberglass masts which make raising these antennas an easy task.

Since I lack the space to erect a 80-Meter horizontal 1/2 wavelength flat top dipole (the familiar "doublet" antenna), I have put that antenna on my …

A 15-Meter Half Square Antenna. Post #221

Now that my 20-Meter half square antenna is performing well, it's time to build its companion for 15-Meters.

The half square antenna is a basic 2-element wire array using two 1/4 wavelength vertical elements connected at the top by a horizontal 1/2 wavelength phasing line.  The antenna is fed in phase and shows bidirectionality, modest gain, and some immunity from noise on its sides.  A ground radial system isn't required.

By feeding the half square in one of the upper corners, we find the current maximum and a fairly good match to 50-ohm coaxial cable.

MATERIALS:

Since my two MFJ fiberglass masts were already being used by the 20-Meter half square antenna, I decided to make two new masts out of those 4-foot/1.21 meters surplus military fiberglass poles you see advertised in the Amateur Radio magazines.  I had enough mast sections to make two, 20-foot/6.09 meters masts.

Two 7-foot/2.13 meters wooden support stakes for the masts.

Number 14 AWG housewire to make the horizontal…

A simple 20-Meter half square antenna. Post #220.

I thoroughly enjoyed my first half square antenna during this past weekend.  Built for 40-meters, the easily assembled antenna exhibited a bidirectional pattern, offered some gain, required no ground system, and was fairly immune to noise and qrm from the sides.  I disassembled the antenna on Monday and stored it for future use.

Now, I wanted to build a similar antenna for 20-Meters, one of my favorite DX bands.  I generally followed the pattern of the earlier half square with a few modifications.

In general terms, the half square antenna is a basic 2-element wire array fed in phase using two 1/4 wavelength verticals connected by a 1/2 wavelength horizontal phasing line running from the top of each vertical element.  According to Rudy Stevens (N6LF), "the theoretical gain over a single vertical is 3.8dBi."  The half square is fed at the top of one of the verticals, where the current is at a maximum.  This arrangement is a good match for a 50-ohm coaxial feed line.

Although …

A Simple 40-Meter Half Square Antenna. Post #219

On Friday, 09 August 2013, I built my first 40-Meter Half Square Antenna.  Several hams I know have used this simple antenna to increase their contacts on 80 and 160 meters.  The antenna provides some gain over a single vertical antenna and offers some signal rejection off the sides.

According to my preliminary research, the half square is a wire antenna with 2 vertical elements fed in phase.  One quarter-wave vertical is fed at a  top corner where its attached by a coaxial center connector (such as the Budwig HQ-1).  The other end of the coaxial connector is attached to a horizontal half-wave phasing line and then connected to another quarter-wave vertical aiming down to the ground.  Both vertical segments are insulated from ground.  The vertical elements are supported by masts or other objects such as trees.  With the antenna being fed at a top corner, the current portion of the antenna is high with a good match to 50-ohm coaxial cable.  No ground radial system is required.
Accordi…

An 80 through 10 Meter doublet antenna. Post #218

Sometimes the simple things in life are best.  This reasoning can be applied to amateur radio antennas, where cost and ease of assembly are factors for your "antenna farm".

As much as I like towers and 4-element monoband HF antennas (I've used them during Field Day events), the cost of such structures can really ruin my retirement income.  So, as I've done in the past, I've designed and built simple antennas that "do the job" without depleting my bank account.  In most cases, limited funds, restrictive operating conditions, lack of space, and proximity to neighbors have dictated easily built antennas such as verticals, inverted vees, delta loops, and small flat-top dipoles.

Recently, my xyl and I were clearing some of her property in the Puna District when I saw two Norfolk Pine Trees separated by approximately 120 feet/36.58 meters.  There was a branch on each tree approximately 50-feet/15.24 meters above ground.  These branches would make a suitable…