BACK TO MAIN MENU
By Art Blick, VE3AHU
11 Manitou Crescent E.,
Reprint from October 97 of TCA
"Plumber's Delight" a simple and economical 2 metre antenna
A few months ago, we received two variations of "standard" antenna designs and consider them worthy of mention.
The first, submitted by Bernard Burdsall, VE3NB, is called the "Plumber's Delight" and is constructed from scrap pieces of half inch copper tubing.
In essence, it is a half-wave dipole fed by 50-ohm coax cable through a gamma match. It also includes a copper tubing support that is a quarter-wave from the antenna elements so that, when strapped to a metal pole or tower, it will increase the forward power in the direction of the antenna elements. See Figure I.
The original design used a small ceramic trimmer capacitor (7-45 pF) with a 5-1/2inch length of No. 14 AWG copper wire, to form the gamma match.
This capacitor will handle 10 watts of RF with no problem. But the capacitor has been replaced with a small 50 pF variable mounted in a small plastic pill box to handle greater RF powers and to overcome probable weather effects.
The design uses a copper "T" fitting to hold the two antenna elements and the support tube together and a 90' elbow, or another "T" fitting, to hold the other end of the quarter-wave support tube and a length of tubing for strapping to the mast or tower. Two stainless steel clamps can be used to strap the support to the mast or tower.
A "proper" two-element Yagi beam could be made by soldering two 20-1/2-inch pieces of tubing into the open ends of the "T" fitting and centrally mounting the antenna on a mast (a wooden or plastic mast if mounted for vertical polarization). See Figure 2
Using the antenna as a Yagi beam will give a forward gain of about 5 dBd (dB gain over a dipole), almost one full S-unit of signal strength (one S-unit = 6 dB).
The SO-239 female coax connector is mounted on the antenna "T" fitting with two self-tapping screws.
A piece of 1/4-inch-thick plastic is mounted on the support tube to hold the gamma match capacitor.
A 3-3/4-inch length of 1/2-inch copper strapping supports the far end of the copper wire. See Figure 3.
The latter is formed around the copper tubing element and held tight by a brass screw and nut.
The antenna does perform well with gain in the direction away from the support mast or tower and it is very simple to tune.
Adjust the gamma match capacitor to obtain an SWR of 1: 1. If a 1: I match cannot be obtained with a 5-1/2-inch length of copper wire, shorten or lengthen it and readjust the capacitor until a 1:1 SWR match is obtained.
It is best to use a 6- to 7-inch length of wire to start and bend the extra length back around the gamma wire until a match is obtained. Then cut off the extra length.
Many hardware and plumbing suppliers have frequent sales of 1/2-inch copper tubing and fittings so building the antenna from scratch should cost less than $10, not counting the cost of the capacitor, coax fittings and cable used.
Most "old-timers" will have such capacitors in their junk boxes and such components and coax fittings can usually be found at Amateur fleamarkets.
BACK TO MAIN MENU
[ TOP ]