                        The SCALE Program
                          May 15, 2000

   Let's say that you have been using YW to analyze a particular 
Yagi, and that you like the response characteristics of this 
particular antenna over a frequency band. SCALE is a utility 
program that uses the same data files used by YW. 

   Note that an earlier N6BV Yagi program called BVYAGI also used 
the same basic YA file format, as did the YO (Yagi Optimizer) 
program. With the introduction of YW (Yagi for Windows), we have 
standardized on a filename extension of YW to distinguish the 
formats. An updated BVYAGI program is included with the CD-ROM 
for the 19th Ed. of The ARRL Antenna Book so that people who do 
not use the Windows 95 or later operating system can still 
evaluate YW files.

   As the name implies, SCALE will scale a YW design to a new 
frequency or to a new taper schedule. It saves the scaled design 
to a new disk file whose name you specify. You may then run YW to 
evaluate this new Yagi over the new frequency band. SCALE can 
also scale YW designs to create disk files compatible with MN or 
AO (Antenna Optimizer) by K6STI, or with NEC2, NEC/Wires, or NEC-
4, the mainframe-like method of moments program.

USING SCALE TOGETHER WITH YW

   When you first bring up SCALE, you will first be asked for an 
input file name. Let's say that you want to create a new YW file 
on the 2-meter band from an existing YW 6-element 20-meter design 
on an 80 foot boom called 620-80H.YW. Type in 620-80, followed 
by [Enter]. 

   After this, the Main Menu will appear on-screen. You will 
choose option number (2) [Enter], since you want to scale the 20-
meter antenna to 2 meters. A submenu will now appear, and you 
will again choose item (2), since you want to scale to a new 
frequency and new element taper. 

   SCALE will now ask for a new frequency. Type in 146.0, 
followed by [Enter], to place the new Yagi design in the center 
of the 2-meter band. You will now be queried whether you want a 
auto-taper or not. Since this design will be used with YW, you 
will answer N [Enter]. (The monotaper concept created using the 
auto-taper function in SCALE will be covered later in the section 
dealing with outputs from SCALE for other programs. Auto-taper 
can be used with earlier versions than 7.0 of the more sophistic-
ated K6STI program called YO, for Yagi Optimizer.)

   SCALE will now ask you to specify the first element by asking 
how many tapered segments you will want. Let's assume for now 
that you want to use 0.188" o.d. rods for your 2-meter elements. 
You will type 1, followed by [Enter], and then .188, followed by 
[Enter]. Follow this procedure for the other five elements. SCALE 
will automatically compute the required length for each element. 

   After you have entered .188 for the last element, number 6, 
SCALE will finish its calculations, and then show on-screen the 
length of the resulting boom, just for reference, asking you to 
give a filename for the new, scaled design. In our example, SCALE 
would compute the new 2-meter boomlength at 7.7 feet. An 
appropriate filename for the new 2-meter Yagi would be 602-8.YWG, 
meaning that it has 6 elements on 2 meters, and occupies an 8-
foot boom. SCALE automatically gives the filename the proper 
extension (*.YW, *.ANT, or *.NEC) depending on the program for 
which the file will be used.

   Next, SCALE will prompt you to enter a comment-line descrip-
tion of the Yagi that it just scaled. You might type in something 
like: "602-8.YW, scaled by SCALE from 620-80H.YW," or something 
like that. As you can see, I usually use the original disk file-
name, with a comment about the scaling that was done. There is 
room for a description 50 characters long. Note that if you 
simply hit the [ENTER] button rather than entering a label, SCALE 
will automatically use the disk filename for the label in the 
resulting file.

   After SCALE has saved the file to disk, it will go back to the 
Main Menu. You will probably wish to exit SCALE and then run the 
resulting data disk file through YW to verify that the automatic 
scaling is reasonable, and that the frequency response is 
appropriate. You will find that the taper schedule used for a 
Yagi has a subtle and not always intuitive effect on the pattern 
as a function of frequency, especially the F/R Ratio and the 
backlobes. In general the bigger the o.d. of the resulting 
element the less the "Q" of that element.

   You may have to run SCALE several times to compensate for 
these subtle effects. SCALE seems to shift the response in 
frequency more for severe taper schedules. Usually however SCALE 
produces designs for new frequencies that are very close to the 
desired results if a reasonable taper is used. 

   Now, let's try another example, scaling a 5-element 20-meter 
beam to 15 meters. We'll use the 520-40M.YW design as the input 
file. Again call up SCALE and enter the file 520-40M when 
prompted to do so. From the Main Menu choose option (2), and then 
option (2) from the submenu. Use a center frequency of 21.225 
MHz, and answer "N" to the prompt asking whether you want a 
monotaper or not. 

   Let's assume that you want to use some aluminum tubing you've 
been hoarding in the basement for just such a moment. You have a 
stockpile of 6 foot lengths of 0.875", 0.750" and 0.625" diameter 
tubing, each having a 0.058" wall thickness so that they will 
telescope together nicely. The center section of each element 
will be a single piece of 0.875" O.D. tubing laid across the 
boom, so that 36" sticks out on either side of the boom. Into 
this will go the 0.750" O.D. tubing, with 6" inserted into the 
larger tubing to create a strong joint. This means that 66" out 
of the total of 72" of the 0.750" tubing sticks out of the 0.875" 
tubing. Into the end of the 0.750" tubing will telescope whatever 
length of 0.625" O.D. tubing is necessary for each element. 


       Section     1        2        3
       Diameter    0.875"   0.750"   0.625"
       Length      36"      66"      variable


   Enter the data above as prompted for each element. SCALE 
computes the overall boom length as 26.378 feet, so an 
appropriate filename for the scaled design would be 515-27.YW, 
and an appropriate label might be "515-27.YW, scaled from 520-
40M.YW." Quit SCALE and call up YW to analyze 515-27.YW. You 
should find that SCALE has produced a very nice design that 
covers the whole 15-meter band well.

   Note: if the overall length of the segments making up an 
element adds up to a length that is longer than that necessary 
for resonance, SCALE will make the end segment a negative number. 
Obviously, this indicates that the next-to-last segment should be 
made shorter than originally specified, or that the operator had 
better pay more attention to his taper schedule. YW will also 
object to such a physically impossible designs!

CREATING DISK FILES FOR OTHER MODELING PROGRAMS

   With SCALE you can also convert a tapered yagi design to an 
equivalent "mono-taper" file that can be used directly by K6STI's 
MN or AO version of the MININEC3 antenna evaluation program, or 
by the NEC2 or NEC-4 antenna program.

   The output files created for MN, AO or NEC2 or NEC-4 will give 
an equivalent diameter (radius for NEC-2 or NEC-4) for each 
element. This diameter will usually be different for each element 
of a tapered design. This is because the program is creating for 
each element an equivalent monotaper that has the same reactance 
at the new frequency as the corresponding tapered element does at 
the original frequency. 

   SCALE will also center the boom of a scaled Yagi design at the 
mounting mast point, 0.000" on the X axis. This allows a program 
like MN, AO or NEC2/4 to evaluate "Christmas Tree" arrangements, 
such as when a 15-meter Yagi is stacked 5 feet over a 20-meter 
beam. Such "short stacks" can cause severe interactions, usually 
altering the performance of the higher frequency Yagi, sometimes 
quite drastically. 

   YW is designed to evaluate strictly single-frequency Yagis, 
rather than stacks of Yagis. On the other hand, the MN or AO or 
NEC2/4 programs are more general-purpose modeling programs, 
although they operate considerably more slowly than does YW. 

