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 |