(Using an *isosceles triangle*)
by Leonard WB3AYW 10/31/06
Originally Published by ARRG.US December 14th, 2006
(Used with permisson from WB3AYW)
This article is not intended to be a complete construction, or "build it" adventure,
but is intended to give you some ideas and good working lengths and spacings for use on various HF ham bands including 2 meters, and should work well when the antenna is properly supported. The antenna is high gain.
In 1996 I had a T-L antenna on the wall for two meters, when one Saturday it fell to the floor, breaking in two pieces. I decided to try a loop antenna and I only had one mounting point on the paneling, so I used tape to make a triangle, but if I used an equilateral triangle as in all of the antenna books, I would have to put a nail in the middle of the paneling; not in the groove. So I used my MFJ 259 antenna analyzer and when I changed the top of the antenna to another groove, the VSWR and the resistance were OK. I then tried a repeater that is about 20 miles away and voila full quieting. Later I checked into the net and no problems; they said it sounded good for an indoor antenna with a handy-talkie. It stayed on the wall and is still there as my emergency two-meter antenna. Then I decided to try the design on 40 meters and it worked! After testing with a three-element beam and the delta loop I then decided that there was not enough signal difference to leave up the beam in the woods.
evening, I was net control for our local ten meter net at 8 PM on
28.330. After several check-ins, I was told that my signal was down,
but steady and readable. I looked at the VSWR meter and it showed a
one-to-one. I then looked at my antenna switch and knew what was
wrong; I was on my 40-meter loop. I switched to my four-element beam
and everyone in the net said I was back to normal. After several
months I checked the delta loop for other bands and it had a three-to-one
VSWR on the worst band from 40 meters to 10 meters that I can
After the 40 meter delta was used on 10 and the VSWR was OK I then decided to build a delta beam for 10 METERS. I decided to point it to the South, so I only had to switch antennas instead of using net time to rotate my beam. I used the same design and it worked OK. I added a reflector and two directors to make it a four-element array. With my beam pointed to the South, signals were the same on both antennas, but the delta was picking up a wider beam width, so when I moved the one end to another tree to fine tune the direction I added two more directors and the beam width was narrowed enough for what I wanted. Now I do not have to rotate my beam all the time during the net.
The cost of my
six-element delta beam was only time; since the wire (you can use any size
that is on hand) that made up my three-element forty-meter beam was
recycled into yet another antenna in the woods. It is nice to have three acres of tall
trees to put my antennas in next to the house.
Then I built another
delta and pointed it to the east for tests. Tests with two-element
delta and a four-element horizontal Yagi at my QTH, with a four-element
Yagi that is on a rotator at W3TO's QTH about twenty air miles to the east
of my QTH. (This test does not take into consideration any feedline
losses because the main purpose is a vertical to horizontal signal report
test for dual polarity in the delta
My radio is a Kenwood TS870S and Jim's (W3TO) is an ICOM 751A.
Horizontal Yagi to horizontal Yagi - S9
Horizontal Yagi to vertical Yagi - S0
Horizontal Yagi to delta - S9
Vertical Yagi to delta - S7
The lowest S meter reading with W3TO's four-element Yagi being rotated and the delta was S3.
This shows that the delta
has an S7 gain and an S3 gain over the Yagi for DX purposes on fadeout
conditions, that is caused by polarity change. The impedance is 50
OHMS and the VSWR is non-existent with the .4 - .2 - .4 isosceles triangle
with no matching network.
refer to sides of loop in drawing below)
Subtract 4% for each director
Tuning notes for lowest swr:
Overall length of the driven element can be longer at first than what the chart above shows,then cut in center bottom and the overall length adjusted more or less as needed. Some trial and error may be done here. Twist ends together and solder when done.
Support ropes at bottom corners may also be slid up or down equally to increase or decrease angle at bottom sides. A combination of these procedures will help tune the antenna for lowest swr.
Editor notes...Since this could be a somewhat complicated antenna to support if multiple elements are used, you may wish to aim it in the general direction of your "most desired direction" and secure it in a fixed position. If you don't have suitable supports for the top and bottom sides, then you will have to modify the supports to suit your needs and location.
If you have the suitable materials and the ability, this would make a very cool multi element beam when used with a rotor or just build the driven element and hang on an inside wall for a great 2 meter emergency antenna or even stealth mode! References:
Definition: (*isosceles triangle*) A triangle with two equal sides. The angles opposite the equal sides are also equal.
ARRL Antenna Book
Edward M. Noll, 73 Vertical Beam and Triangle Antennas
VE3GEJ, 73 Magazine, June 1972. "Six elements on twenty meters. pp 17-20
My thanks to W3TO for testing and for the reports from N4WCK in Georgia, WA3PGL and W3AGF in Florida for signal reports, as this antenna was developed and WA3HDK for his support.