Click
spreadsheet to download all files in ZIP format
As
a convenience to builders of the
log periodic antennas described on this site, permission
to download the copyrighted software for mechanical and electrical
design of antenna elements (in IBM PC format) has been granted
by the ARRL.
The associated book is by David B. Leeson, W6QHS (now W6NL),
"Physical Design of Yagi Antennas". This text and
copyrighted software are available from the ARRL. The book is
ARRL # 3819. The software on floppy disk is available separately
as #3827 IBM PC or #3843 Macintosh.
Spreadsheet
Update
Sept. 17, 2003
Dave Leeson, W6NL contributed these comments along with
new spreadsheets.
As
you may know, when I wrote the Yagi book the current revision
of the EIA tower standard at that time was EIA222C. Subsequently,
they upgraded their treatment of forces on cylinders in
yaw, and the current revision EIA222F has a more accurate
model for wind forces (it also has a slightly different
treatment of cylinder drag coefficient and gust statistics,
but the effect of this is minimal).
Essentially,
the new spec takes account of the issue that almost all
the force from air on a cylinder is due to pressure variation,
not viscous force. So no matter what the distribution
of pressure around the a mast, boom or element almost
all the force is perpendicular to the surface. This would
affect the calculation of boom force and equivalent area
(it would be the greater of element or boom area rather
than the square root of the sum of the squares), which
would modify the mast calculations. This has no effect
on the element calculations.
I've done some experiments with PVC elements and booms
stuck out the sunroof of a moving car that satisfy me
that this is a reasonably accurate model (I caution my
grad students not to confuse a model with real life!).
Kurt Andress, K7NV, author of YagiStress, concurs with
the use of the new model for boom and mast calculations,
and suggests a simple supporting experiment holding a
PVC pipe cylinder out the side window of a car.
Under the EIA222 model, all wind force on cylindrical
parts is perpendicular to their axis, so that in an oversimpified
picture all element force is directed along the boom.
However, there is vertical gusting that must be considered
(most boom failures I've seen are from the boom blowing
up and breaking at the center). I use an estimate of 15
degree angle above or below horizontal for winds over
flat ground and 30 degrees for hilly sites. I've revised
the mast and boom spreadsheets to reflect the slightly
lower forces from the EIA222F model. The new ones are
MastF.wk1, Mast2F.wk1
and BoomF.wk1.
If
you set the vertical gusting angle to zero on the BoomF.wk1,
you get the "boom force only" situation that ignores the
potential effect of the elements.

W6NL SPREADSHEETS FOR PHYSICAL DESIGN
OF YAGI ANTENNAS
From
the readme file on the original distribution diskette:
The
accompanying spreadsheets are in the Lotus 123 WK1 format.
They are also available in Macintosh Excel format. Be sure to
make a backup copy before you change anything, as these files
are not protected. The following spreadsheet files are included:
AREA.WK1
Calculates element areas from section dimensions
ELEMENT.WK1 Calculates element wind and ice survival
BOOM.WK1 Calculates boom survival and torque balance
MAST.WK1 Calculates mast survival
MAST2.WK1 Calculates multisection mast survival
SLOPE.WK1 Calculates sloping foreground reflection gain
Start
with your Yagi antenna dimensions (the manufacturer's manual
is a good place to start, but you may have difficulty finding
wall thicknesses). Open AREA.WK1 and enter the element dimension
information. This will calculate the element areas.
To use ELEMENT.WK1, enter the same information for any element
into that spreadsheet. It will calculate the wind and ice survival
speeds. You can experiment with different section lengths, and
you can add additional internally reinforced sections (increased
wall thickness). You will find that the best design is a balance
between wind and ice survival; for the strongest element of
a given length and weight, work to make the survival speeds
the same for all sections.
ELEMENT.WK1 also contains the W6QHS taper algorithm, which can
be used to convert a cylindricalelement Yagi design (as generated
by several popular Yagidesign computer programs) to the mechanically
stronger tapered format. This algorithm can also be used to
adjust dimensions of strengthened elements so they provide the
same reactance as the original tapered elements on which they
are based.
To use BOOM.WK1, enter the element area data from AREA, and
enter the element spacing and boom dimensions. BOOM will calculate
the boom survival speed for both unguyed and guyed configurations.
You will need to become familiar with the required dimensions
to enter, such as the boom guy attachment points and brace offset.
Use this spreadsheet to maximize boom survival by experimenting
with different section diameters and wall thicknesses. You can
enter up to five boom sections, and you can make the reflector
and director sides asymmetrical.
BOOM.WK1 also calculates the element and boom torque balance,
and suggests dimensions for the compensating element. As you
become familiar with BOOM, you will see how to use boom compensating
sleeves to compensate for balun and coax moments. For simplicity,
BOOM does not consider ice loading.
MAST.WK1 calculates mast survival from mast dimensions and antenna
areas. Enter the dimensions and yield strength of the mast.
For each antenna, enter the total element effective area, the
boom effective area and the location on the mast. MAST2.WK1
uses the same techniques as ELEMENT and BOOM to calculate survival
of multisection masts.
SLOPE.WK1 calculates groundreflection gain for an antenna above
a sloping foreground. Enter the frequency in MHz and the height
of the antenna above the intersection of the slope line extended
to the tower. Alternatively you can calculate the effective
height for a tower set back from the edge of the slope. This
worksheet also calculates, for the angle of maximum radiation,
the center and limits of the ground reflection (Fresnel) zone.
These spreadsheets are quite rudimentary. If you are familiar
with spreadsheet development, you can link them and expand their
usefulness. For more information, see the book "Physical
Design of Yagi Antennas," published by the ARRL (ARRL order
no. 3819). Copyright © 1992 The American Radio Relay League.