Cheap Yagi Antennas for VHF/UHF
by Kent Britain, WA5VJB
edited by
John Maca, AB5SS
[Editors notes: The antennas described
in this article were built as the result of several discussions between
Kent and a Cuban radio operator. While there are plenty of high
performance antenna designs, most of the parts required to build them are
not available in Cuba. There just isn't an EPO or Radio Shack available in
Cuba. Kent accepted this as a challenge to design a really good antenna
that could be built with little more than ground wire, coax and a wooden
boom. Using the latest antenna design software, he has developed several
variations for 144 thru 1296 MHz. Apparently, the designs work very
well... Kent entered the 432 MHz version in a recent antenna contest and
lost by 0.2 dB to a Midwest ham who had copied his design. Though
disappointed in losing, it did prove to Kent that the antennas can be
easily replicated with consistant performance.]
If your
planning to build an EME array, don't use these antennas. But, if you want
to put together a Rover station with less than $500 in the antennas or
just want a good antenna for the home, read on.
These antennas are
relatively small, easily constructed from common materials/tools and have
surprising performance. The feed method is greatly simpified by directly
soldering the coax to the driven element. No baluns or gamma matches are
used in this design. This simplified feed uses the structure of the
antenna itself for impedance matching. The spacing of the director and
reflector elements from the driven element directly affects the feed point
impedance of the antenna. So, the design starts with the feed (driven
element) and the elements are built around it. Typically, a high gain
antenna is designed in the computer, then you try to come up with a
matching arrangement for a 31.9 Ohm feed! For the cost about 0.5 dB of
gain, these antennas make some design compromises for the feed impedance,
use an asymmetrical feed and make trade offs for a very clean pattern.
But, they allow simple measurements, have wide bandwidth, the ability to
grow with the same element spacing AND... you can build these antennas for
$5!!!!
The booms used for these antennas is 1/2" X 3/4" wood. The
elements have been made from silicon bronze welding rod, aluminum rod,
hobby tubing and solid ground wire with no change in performance. Since
you want to be able to solder to the driven element, silicon bronze
welding rod, hobby tubing and #10 or #12 solid copper wire have been used
and work fine. A drop of "Super Glue", epoxy or RTV is used to hold the
elements in place. A good coat of Polyurethane should be applied to the
wooden boom to protect it from the weather. A polyurethane varnished 902
MHz version has been in the air for a year now with little deterioration
in performance.
And now for the antenna designs. These antennas
have been carefully designed to have the highest dB's/Dollar ratio of
anything around They were designed with YagiMax, tweaked using NEC and the
driven elements experimentally determined on the antenna range. The driven
element design is the same for all frequencies except for the length (L)
and separation (H). See Figure 1 for details on the driven element. All
dimensions are in inches. 
144 MHz. This antenna is peaked for
144.2 MHz but performance is still good at 146.52 (emergency use only!)
Driven element dimensions are L = 38.5" and H = 1.0" Elements are 1/8"
diameter.
| 144 MHz | REF | DE | D1 | D2 | D3 | D4 | |
| 3 Element | Length Spacing |
41.00 0.00 |
8.50 |
37.00 20.00 |
|||
| 4 Element | Length Spacing |
42.00 0.00 |
8.50 |
37.50 19.25 |
33.00 40.50 |
||
| 6 Element | Length Spacking |
40.50 0.00 |
7.50 |
37.50 16.50 |
36.50 34.00 |
36.50 52.00 |
32.75 70.00 |
222 MHz. This antenna is peaked for 222.1 MHz but
performance bearly changes at 223.5 MHz. Driven element dimensions are L =
24.5" and H = 1.0" Elements are 3/16" diameter.
| 222 MHz | REF | DE | D1 | D2 | D3 | D4 | |
| 3 Element | Length Spacing |
26.00 0.00 |
5.50 |
23.75 13.50 |
|||
| 4 Element | Length Spacing |
26.25 0.00 |
5.00 |
24.10 11.75 |
22.00 23.50 |
||
| 6 Element | Length Spacing |
26.25 0.00 |
5.00 |
24.10 10.75 |
23.50 22.00 |
23.50 33.75 |
21.00 45.50 |
432 MHz. This antenna is peaked for 432.1 MHz.
At this frequency, this antenna is getting very practical and easy to
build. Driven element dimensions are L = 13.0" and H = 3/8" Elements are
1/8" diameter.
| 432MHz | REF | DE | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | D9 | |
| 6 Element | Length Spacing |
13.50 0.00 |
2.50 |
12.50 5.50 |
12.00 11.25 |
12.00 17.50 |
11.00 24.00 |
|||||
| 8 Element | Length Spacing |
13.50 0.00 |
2.50 |
12.50 5.50 |
12.00 11.25 |
12.00 17.50 |
11.00 24.00 |
12.00 30.75 |
11.25 38.00 |
|||
| 11 Element | Length Spacing |
13.50 0.00 |
2.50 |
12.50 5.50 |
12.00 11.25 |
12.00 17.50 |
12.00 24.00 |
12.00 30.75 |
12.00 38.00 |
11.75 45.50 |
11.75 53.00 |
11.00 59.50 |
902/903 MHz. This was the first antenna I
built using the antenna to control the driven element impedance. The 2
1/2' length has proven practical, so I haven't built any other versions.
Driven element dimensions are L = 5.7" and H = 1/2" Elements are 1/8"
diameter.
| 902/903 MHz | REF | DE | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | |
| 10 Element | Length Spacing |
6.20 0.00 |
2.40 |
5.60 3.90 |
5.50 5.80 |
5.50 9.00 |
5.40 12.40 |
5.30 17.40 |
5.20 22.40 |
5.10 27.60 |
5.10 33.00 |
1296 MHz. This antenna is the veteran of
several "Grid Peditions" but I have yet to actually measure the gain.
Dimensions must be followed with great care. The driven element is small
enough to allow 0.141 semi-rigid coax to be used instead of RG-58. Silicon
Bronze welding rod was used for the elements but any material can be used.
Driven element dimensions are L = 4.0" and H = 1/2" Elements are 1/8"
diameter.
| 1296 MHz | REF | DE | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | |
| 10 Element | Length Spacing |
4.30 0.00 |
1.70 |
3.90 2.80 |
3.80 4.00 |
3.75 6.40 |
3.75 8.70 |
3.65 12.20 |
3.60 15.60 |
3.60 19.30 |
3.50 23.00 |
OTHER VERSIONS
421.25 MHz
ATV. 421 MHz Vestigial Sideband video is popular in North Texas
for receiving the FM video repeaters. The driven element for these
antennas is designed for an impedance of 75 ohms. So RG-59, or an `F'
adapter to RG-6, can be directly connected to a cable TV converter/Cable
Ready TV on channel 57. Driven element dimensions are L = 13.0" and H =
1/2" Elements are 1/8" diameter. Spacing is the same for all versions.
| 421 MHz ATV | REF | DE | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | D9 | |
| 6 Element | Length | 14.00 | 12.50 | 12.25 | 12.25 | 11.00 | ||||||
| 8 Element | Length | 14.00 | 12.50 | 12.25 | 12.25 | 12.00 | 12.00 | 11.25 | ||||
| 11 Element | Length Spacing |
14.00 0.00 |
3.00 |
12.50 6.50 |
12.25 12.25 |
12.25 17.75 |
12.00 24.50 |
12.00 30.50 |
12.00 36.00 |
11.75 43.00 |
11.75 50.25 |
11.50 57.25 |
450 MHz FM. Yea, I understand it's FM, but
sometimes a newcomber needs a cheap antenna to get into a repeater or give
you a simplex QSO during a contest. Driven element dimensions are L =
12.0" and H = 3/8" Elements are 1/8" diameter. Spacing is the same for all
versions.
| 450 MHz FM | REF | DE | D1 | D2 | D3 | D4 | |
| 6 Element | Length Spacing |
13.00 0.00 |
2.50 |
12.10 5.50 |
11.75 11.00 |
11.75 18.00 |
10.75 28.50 |
435 MHz AMSAT. The larger versions have not
been fully tested and I appreciate the help and motivation from KA9LNV for
these antennas. Updates and performance evaluations are planned for a
later edition of the AMSAT Journal. A high Front-to-Back ratio was the
major design consideration for all versions. The computer predicts 30 dB
F/B for the 6 element and over 40 dB for the others. NEC predicts 11.2,
12.6, 13.5 and 13.8 dBi for the 6, 8, 10 and 11 element respectively.
Using 3/4" square wood makes it easy to build two antennas on the same
boom for cross- polarized operation. Offset the two antennas 6 1/2" and
feed in phase for Circular Polarization. Or, just build one antenna for
portable operation. Driven element dimensions are L = 13.0" and H = 1/2"
Elements are 1/8" diameter. Spacing is the same for all versions.
| 435 MHz AMSAT | REF | DE | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | D9 | |
| 6 Element | Length | 13.40 | 12.40 | 12.00 | 12.00 | 11.00 | ||||||
| 8 Element | Length | 13.40 | 12.40 | 12.00 | 12.00 | 12.00 | 12.00 | 11.10 | ||||
| 10 Element | Length | 13.40 | 12.40 | 12.00 | 12.00 | 12.00 | 12.00 | 11.75 | 11.75 | 11.10 | ||
| 11 Element | Length Spacing |
13.40 0.00 |
2.50 |
12.40 5.50 |
12.00 11.25 |
12.00 17.50 |
12.00 24.00 |
12.00 30.50 |
11.75 37.75 |
11.75 45.00 |
11.75 52.00 |
11.10 59.50 |