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YS Version 2.15

The Ultimate Yagi Mechanical Design Software
By Kurt Andress, K7NV























                                     Don't let this happen to you!


YagiStress (YS) is a full featured, graphical, user friendly program that performs structural analysis on horizontally polarized yagi antennas constructed from round tubular sections. 

YS can work in Imperial or Metric Units, and is likely to tell you more about a yagi antenna than you ever thought you needed to know.

YS has been used by commercial manufacturers and premier station builders for several years. You can have the same tool to complete your antenna designs. No more guess work or trial and error methods! 

If you are serious about Yagi antenna design (I.E. You actually intend to build one), you should not leave your mechanical fortunes to chance!

Here are some YS commercial users:

bulletHygain Antennas
bulletForce 12 Antennas
bulletCushcraft Antennas
bulletCal-Av Labs
bulletKMA Antennas
bulletDX System Radio


YagiStress Website <click to learn all about it.

You can obtain a free Demo version of YS by clicking here YS DEMO.

To use your free YS Demonstration program.
Save the YSdemo1.zip file to a directory of your choice.
Unzip the file with WINZIP to a directory such as YS_Demo. You should see two files, YS.exe is the program and YSDOC.txt is the operating manual.

Then type YS at a Dos Promt, or open one in Windows by double clicking on the file.

The YS Demo & YS program are DOS based software. They were not written for the Windows environment, but may be run as a Windows 95/98 DOS application. They will not mess up your Windows system and are easily erased. 


May the "Forces be with You"

73, Kurt


What is the difference in YS and YS PRO?

YS Beta Test Version 2.5X For Professional Users
Latest rev date 4-10-03

While I do everything I can to make sure the upgrades are functioning properly,
this is still considered a development version of the program.


YS now performs analyses according to several design spec's.
The spec can be selected by the user.

The current spec's are:

EIA-222-C Old Basic Wind Speed standard, loads generated from Basic
Wind Speed values, includes 1.30 gust factor. Represents current
commercial antenna design methodology, if the designers are
using the "Crosswind Principle." I can't verify that all of
them are. Drag coefficients from the spec applied.

EIA-222-F Current EIA spec, loads generated from Basic Wind Speed
values including height/exposure and gust factors.
"Crosswind Principle" applied. Drag coefficients from the
spec applied.

UBC 1997 Current UBC spec, loads generaterd from Basic Wind Speed
values including specified gust, height, and exposure factors.
"Crosswind Principle" applied. Drag coefficients from the
spec applied.

No Spec Peak Wind Speed design, no additional factors applied.
Uses the generally accepted drag coefficients for flat and
cylindrical members.

You guys may have some questions about the stuff you see on the screen,
let me know. The wind speed formulas and drag coefficients are displayed
for each spec.
I haven't tried the British spec CP3, as I don't have enough of it to do
it properly.
The fun will come down the road, as I hear that both UBC and EIA are going
to be coming out with new spec's within the next year or so.
Hopefully, I have configured the code properly to make upgrading the code
as painless as possible.

UBC is the only spec in the group that has 3 different exposure criteria
added to the wind pressure formula.

They are:

B - Shielded exposure with buildings, or other natural features within 1 mile
of the site.

C - Flat open terrain extending 1/2 mile from the site.

D - Severe exposure, 80 Mph Basic speed and up, flat unobstructed exposure
within 1/4 mile of large bodies of water.

After playing with it a bit, it is interesting to see that UBC "D" exposure
produces nearly the same loading as EIA-222-F. Both spec's require antenna
height to determine the wind pressures.
222-C and "No Spec" are not height dependent.

UBC '97 states that EIA-222 is a recognized spec, and proof of satisfying
the EIA spec constitutes compliance with UBC. That's some good news, and
makes sense, as EIA-222-F is equivalent to the most severe UBC exposure.

For those of you that may be familiar enough with the new UBC code, to wonder
how I transformed the tabular parts of the spec into YS....
Using a great little program I ran across years ago, I came up with some
linear equations that are identical in form for each of the UBC exposures.
The equation constants, for each of the exposures differ.
These formulas produce values with a standard deviation of .0025 from the
tabular values in the spec. The tabular values in the spec are rounded to 2
decimal places, so the equation generated values should be close enough.
These are the combined height, exposure, gust factor coefficients that appear
in table 16-G.
The stagnation pressure in table 16-F is really .002562 V^2, when rounding
errors are accepted.

The "No Spec" option is a simple straight forward look at peak wind speed
survival. The others are based on Basic Wind Speed values, for one mile of
wind across the structure, with a general expectency of having the
condition occur in a 50 year period. The Basic Wind Speeds are normally
chosen from the tables or maps of the various spec's.

The idea is that one has already, or will be installing a tower to hold
the antennas, that has been designed in accordance with one of
these spec's. The most likely candidates are EIA-222-F and UBC '97.
EIA-222-C is there just for comparative evaluation with what was done in the past by
some of the commercial antenna builders and may still be done.

If a tower is designed to a specification, it would make sense to design the
antenna according to the same criteria.

Once the antenna has been designed, one needs to use the projected area
figures provided for the antenna to evaluate the tower loads.

It is important to note that this is different than what is currently
done with commercially built amateur antennas. Most of these values are
effective areas normally reduced to 2/3 of the projected areas, in accordance
with the old EIA-222-C spec. For some commercial antennas, we have no idea
what the area figures mean! Some may still be using the Pythagorean formula to
determine area.

It has been a fair amount of research and work to roll all this into the code,
but I think what is here is ok.

YS now sports a coax database, compliments of Press Jones, N8UG, for user
convenience. I asked Press for his recommendations for all coax
that would be suitable for use in the section that forms the flexible loop
around the mast, and connects the antenna to the feedline running up the
Let me know if you think the database is missing any popular suitable

Following suggestions from Eric, N7CL, I have pitched the old "New Antenna"
model building routine. It was a pain to write, and a pain to use.
Now, when you select the New Model option, YS just loads the file named
NEWMODEL.YS2. Then you just go about using the normal YS editing features to
create a new antenna. You can customize the NEWMODEL file to be whatever
you think is a good place to start from.
This got rid of a bunch of code that made room for new stuff.

George, K5TR, asked for a "copy element" function in the normal editing
mode. Since, I 86'ed the new model building routine, I added "Copy Element" to
the "E"lements options. Now, when you are making a new model you can define
a taper schedule for one element, and then copy it to all the others, then go
to each one and adjust the locations and lengths to get what you want.

YS Beta Test Version 2.51 2-06-00

Fixed a problem found by N7CL, that would crash the program if a very short
section was placed at the end of the boom.

The Safety Factor check mark was not getting erased in the Torque screen. N7CL

After changing the Safety Factor, the program was reanalyzing the antenna,
but not updating the new element wind speed. N7CL

Imposed height limits on the wind speed spec's. The UBC charts cover 10'-400'.
My equations are accurate in that range. N7CL

The units for entering height are fixed at Feet or Meters, and are independent
from the YS units toggling feature "U".

Added another element resonance method. K6STI provided me with a subroutine to
generate a monotaper equivalent element via W6NL's (ex-W6QHS) method. Another routine
from Brian calculates the self impedance angle of the element.
This is ATAN(zi/zr), zr = self-resistance, zi = self reactance.
This method of maintaining element resonance is much more accurate.
The W6NL or W2PV method may be selected by using the Frequency option from the
main menu.

I added a little convenience feature to the element resonance display. It
tells you whether the element needs to be lengthened or shortened to get
back to the original resonant frequency.

A dozen or so display changes and housekeeping.

K6STI sent me the latest version of ED.exe for editing notes. I changed the
screen text lines when shelling out to it, so it should look better.

YS Beta Test Version 2.52 4-24-00

1) Fixed some errors in the various windspeed spec algorithms. These are
correct now and all track exactly with the various methods.

2) Fixed bug, when changing alloy, YS did not automatically reanalyze antenna.

3) Added a program configuration file YS.CFG. This lets you declare a default path to the
YS model files. This allows you to keep all your models in a Directory, like My Documents\YS,
that you frequently back up,
You can select either "I"mperial or "M"etric units for the default.
You can set the default taper algorithm to "W2PV" or W6NL".
The rest of the lines set the default units for the various display screens.
- is for small units (inches/mm), + is for large ones (feet/meters).

4) Fixed a bug that caused loading the newmodel file to crash.

5) Fixed bug in element display screen when "next element" was used.

6) Other minor housekeeping and little display bug fixes.

YS Beta Test Version 2.53 2-7-02

1) Added alarm deactivation to YS config file. "+" activates the audible alarm, "-" turns
the alarm off.

YS Beta Test Version 2.54 4-10-03

1) Added a switch to turn gravity off/on. Press "G" in the main menu and it will the toggle
the feature. This is used to design a freestanding vertical element.