Photo: Similar 10 element Yagi antenna
The antenna describe here has proved itself as one of the best I have used through the years. This antenna has won many VHFcontests through the years and has withstand severe weather along the Southern Cape Coast known for its stormy weather in winter. Constructing this antenna is straight forward, to the point and you should not have any problems if you stick to the basic rules of antenna construction. This antenna is a 14 element closed-spaced two meter beam. It features high forward gain accociated with a narrow beam width. It has a excellent front to back ratio and is especially suited for DX contacts where maximum gain and narrow beam width is required.
Boom Length: 4.72 meter
Longest Element: 1000 mm
Turning Radius: 2.42 meter
Wind Survival: 120 km/ph
Mast Diameter: 41 mm to 52 mm
Boom Diameter: 32 mm (round); 25mm x 25mm x 3mm (square)
Weight: 3.5 kg
Gain: 15.2 dBi (13.0 dBd)
Front-to-Back Ratio: 20dB
Maximum SWR: 1:2 – 1
Band Width: 4 Mhz
Maximum Power: 250 watts continuous, 500 watts P.E.P.
Impedance: 50 ohms ( with balun)
All dimensions are in millimeters and all the aluminum, nuts, bolts, u-bolts, screws and teflon are locally available in South Africa at hardware stores. Be careful when you buy the aluminum. Ensure that the diameter of the aluminum is the correct size. Measure before you buy!! The elements have 12mm and 6.5mm diameter while the boom is 25mm x 25mm. Now lets look at the element table before we start the contruction proses.
|Element||Element Position||Element Length|
|Reflector||30mm (tip of boom)||1000mm (6.5mm)|
|Radiator||355mm||852mm (2 x 426mm) (12mm)|
12 x 22mm x 5mm Stainless Steel Self tapping Screws
5 x 42mm x 4 mm Stainless Steel Machine Type Bolts
8 x 4mm Machine Type Nuts
3 x 52mm x 4 mm Stainless Steel Machine Type Bolts
12 x 4mm Stainless Steel Washers (plain)
12 x 4mm Stainless Steel Spring Washers
3 x SO239 Sockets
1 x 100mm x 25mm Angle Aluminum for SO239’s
2 x 12mm Plastic End Caps to fit over driven element
26 X 6.5mm Plastic Caps to fit over elements
2 x 54mm x 6mm Stainless Steel Bolts
2 x 6mm Stainless Steel Washers (plain)
2 x 6mm Stainless Steel Spring Washers
1 x 6 meter 25mm x 25mm Aluminum Square Tubing (Boom)
2 x 6 meter 6.5mm Aluminum rod for Elements
1000mm x 12mm Aluminum tube for Driven Elements
2 x 25mm x 25mm Plastic End Cap to fit over or into the Boom
2 x U- Bolt TV Clamps
3 x PL259 Connectors
1 x 770mm RG213 Co-Ax Cable for balun
1 x 150mm x 25mm x 15mm Teflon Insulator
12 x 3mm x 10 mm Stainless Steel Machine Type Bolts (For SO239 fastening)
1 x 3.2mm x 500mm Aluminum Braizing Rod (For Hairpin Match)
1 x 130mm x 100mm x 5mm Aluminum Plate (Mounting Bracket)
1 x 100mm x 25mm x 3mm Aluminum Plate (Mounting Bracket Washer)
10 x Cable Ties (Tie RG213 Balun to Boom)
1 x 50mm x 10mm x 2mm Alumiinum Plate (Attaching plate (clip) for Hairpin Match)
I start off with measuring the boom length, marking the element placements and center punching the spot were the holes will be drilled for the elements. One word of advice, never drill through both sides of the boom at once. First drill one side then the other side. This will ensure a centre hole on both sides. After measuring and punching I drill the holes, first with a pilot drill (4mm) and then with the correct size (6.5mm) to fit the elements. Holes drilled, it is now time to drill the 4mm holes that will affix the elements to the boom.
Affix the boom-to-mast clamp and install the U-Bolts. Nearly ready, but we haven’t finish the installation of the balun to antenna connections. Refer to the photo
for this process. Ensure good soldering joints to the SO-239 connectors and use terminal lugs to affix to the driven element. (See photo) Waterproof the coax connections with Coax-Seal or some similar substance. Install the plastic caps on the ends of hte boom, driven element and elements. Use the 2 cable ties to secure the balun to the boom and more cable ties to tie the feedline to the boom and to the mast. Be sure to insultate any connections from the boom or the mast. This completes the assembly procedures.
Driven Element: The SWR can be lowered ot less than 1.2:1 at a desired frequency by carefully trimming the driven element. Keep the element symmetrical by cutting the same amount from each side. Typical SWR under normal conditions is 1.2:1. Each installation however is different, so cut the driven element for the lower SWR at your particular location. Measure the SWR as close to the antenna as you can for accurate results. The SWR should be measured with the mast at right angles to the elements. With the dimensions and material I used an 1.2:1 SWR was obtained.
As already mentioned this antenna is a real contest winner and especially suited for DX. Why wait, get the aluminum and build this antenna and you will be surprised by it’s “performance”. Hope to hear you on 144.400 Mhz soon!!
TEST RESULTS: UPDATED: 26 March 2008!
The 10 Element 2 Meter Beam (front page photo) was installed and tested today (26 March 2008). Unfortunately I do not have a MFJ Antenna Analyzer, but trust that somebody will sponsor me with one soon. (Wishfull thinking??) So the only equipment I have to really test this antenna is the old faithful SWR meter and Field Strength meter. This equipment have tuned many antennas in the past and this time was no different. The following chart show the Bandwidth/SWR/Frequency of the antenna I constructed. The only difference is that I used 10mm tubing for the reflector and the driven element. I obtained the following measurements:
SWR CHART: FREQUENCY 144.400 Mhz – 147.400 Mhz; 50 WATT RF; ANTENNA HORIZONTALLY POLARIZED; 6 METERS OFF THE GROUND
|144.400 Mhz||1.3 : 1||146.300 Mhz||1.1 : 1|
|145.000 Mhz||1.3 : 1||146.400 Mhz||1.1 : 1|
|145.200 Mhz||1.2 : 1||146.500 Mhz||1.1 : 1|
|145.300 Mhz||1.2 : 1||146.600 Mhz||1.1 : 1|
|145.400 Mhz||1.2 : 1||146.700 Mhz||1.1 : 1|
|145.500 Mhz||1.2 : 1||146.800 Mhz||1.2 : 1|
|145.600 Mhz||1.2 : 1||146.900 Mhz||1.2 : 1|
|145.700 Mhz||1.2 : 1||147.000 Mhz||1.2 : 1|
|145.800 Mhz||1.1 : 1||147.100 Mhz||1.2 : 1|
|145.900 Mhz||1.1 : 1||147.200 Mhz||1.2 : 1|
|146.000 Mhz||1.1 : 1||147.300 Mhz||1.3 : 1|
|146.100 Mhz||1.1 : 1||147.400 Mhz||1.3 : 1|
|146.200 Mhz||1.1 : 1||Bandwidth:||3 Mhz|
The Field Strength Meter confirmed an excellent front-to-back ratio with very little RF at the back of the antenna, but a full scale reflection on the meter in front of the antenna. Very little reflection of the meter was noticed on the sides of the antenna. I did not trim the driven element and the current length is as indicated in the construction section.
The following radio amateurs have used this antenna in contests:
Nico ZS4N – Antenna Measurements
Johan ZS2I – Photos of Antenna Components
Pieter ZR6AHT – Questions and Comments