WELCOME TO YU7EF ANTENNA
144 MHz LOW TEMPERATURE ANTENNAS
a large number of radio-amateurs has shown interest in my antennas
after basic characteristics were published in VE7BQH G/T chart,
and I am not able to answer numerous e-mail requests for data, I
have decided to publish the complete data and make them available
for all those willing to build and use my antennas.
the design of these antennas, the main focus was put on obtaining
an as low as possible isotropic temperature of the antennas and as
much as possible gain for given boom length resulting in best
possible G/T ratio. From all of these antennas would be possible
to get some more gain with sacrifice of temperature, bandwidth or
poor impedance. All antennas are optimized for pure 50 ohm feed
impedance with minimum possible reactance to avoid need for some
of specific feed solutions and impedance transformations such as
Gamma Match, T-Match, Hairpin etc. This way all antennas have very low
internal loss and very good efficiency.
up to 3 WL are mostly designed as width band designs, having in
mind that they can be used as a single antenna for the majority of
average users for every day use, by covering 144 – 146 MHz with
reasonable SWR. Longer antennas, however, are designed for a
rather narrow band as I would not expect someone to build a 4 or 5
WL antenna to use it for FM, but only for „low signal“
communications such as tropo DX, MS and EME at 144.0 – 144.5
every antenna there is a table of FREE SPACE dimensions for
elements diameters of 4, 5, 6, 8 and 10 mm – sizes most used.
Note that the driven element size is 10 mm in ALL cases and it is
for OPEN DIPOLE. As it is obvious from specifications, the use of
larger element diameters is recommended due to better
specifications (lower internal loss and better efficiency) but
also because of better mechanical strength, much more
to bending and damage by wind, ice and particularly birds.
Difference in weight of the antenna with 5 mm wire elements and
the one with 8x1 mm tubing is insignificant and one would not get
anything but a mechanically weaker antenna. My recommendation is
to use the 8 mm tubing whenever possible for best results.
on boom diameter used and type of element mounting, the element
lengths from the table need to be corrected accordingly. Boom
correction by DL6WU formula has proven to be reliable over the
years and the attached table shows the correction values for wide
range of boom sizes commonly used by hams.
every antenna, the tables show basic antenna specifications as
well as recommended E and H plane stacking distance for best G/T
ratio. With these stacking distances, a 4 yagi bay stacking gain
is generally about 5.9 dB compared to a
single antenna and with first side lobes down to 11 – 12 dB.
It is recommended that the stacking distance should be kept
from -10% to +5% of the optimum spacing for best results and
acceptable degradation of gain, temperature and G/T ratio of the
system. With every antenna there are also attached single antenna
H and E plane radiation patterns.
noted that Ta and G/T values in my tables are a bit different from
values shown in VE7BQH chart. Values in VE7BQH chart are all
calculated with „Yagi Analysis“ 3.54 that has tendency of
small error, making results more optimistic, probably from not
taking in account material elements loss, while all values for Ta
and G/T in my tables are calculated with program TANT
by YT1NT which is more precise – particularly when calculating
values for a 4 yagi bay. All values for Ta and G/T are calculated
for antennas elevated at 30° as recommended by DJ9BV and as it is
in YA program
recommendation is to always build antennas with INSULATED elements
THROUGH the boom since such a way of
construction is a good guarantee for many years of reliable
operation of the antennas without change in performance.
though driven element length in tables is given for open dipole,
my recommendation is to build antennas with folded dipole due to
many advantages compared to open dipole, except simplicity. With
folded dipole all you need is the use of classic WL/2 * k, 4:1
tolerances need to be kept as low as possible and by all means
should not be more than 1 mm while tolerance of ±0.5 mm will give
you perfect results and calculated specifications.
attention should be pointed to spacing measurement, and it always
has to be done as shown in the table -
cumulative. Never calculate separate spacings and measure it that
way since any measuring errors will accumulate and you will end
up with an antenna that is not what has been designed and
large number of these antennas has been built and used by hams
with excellent results.
any further questions and information feel free to contact me on
my e-mail :
would appreciate any feedback about Your experiences and results
as well as pictures, to be used for future projects and possible
corrections and modifications on existing designs.
All these designs are the result of many years' hard work and they represent
the intellectual property of the author. Distribution and
publishing of these data and information is permitted ONLY for
radio-amateur purposes and construction. Use of these information
and data for any commercial purposes is strictly prohibited
without the written authorization of the author.