                        The SCALE Program

   Let's say that you have been using YA 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 YA. (Note that an 
earlier Yagi program called BVYAGI also uses the YA file format, 
as does the YO (Yagi Optimizer) program.)

   As the name implies, SCALE will scale a YA 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 YA to 
evaluate this new Yagi over the new frequency band. SCALE can 
also scale YA designs to create disk files compatible with MN or 
AO (Antenna Optimizer) by K6STI, or with NEC2 or NEC/Wires, the 
mainframe-like method of moments program.

USING SCALE TOGETHER WITH YA

   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 YA file 
on the 2-meter band from an existing YA 6-element 20-meter design 
on an 80 foot boom called 620-80H.YAG. Type in 620-80, followed 
by [Enter]. 

   After this, the Main Menu will come up 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 YA, 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 the more sophisticated K6STI program called YO, 
for Yagi Optimizer, but not for YA.)

   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.YAG, 
meaning that it has 6 elements on 2 meters, and occupies an 8-
foot boom. SCALE automatically gives the filename the proper 
extension (*.YAG, *.ANT, or *.NEC) depending on the program for 
which the file will be used.

   Next, SCALE will prompt you to enter a comment-line 
description of the Yagi that it just scaled. You might type in 
something like: "602-8.YAG, scaled by SCALE from 620-80H.YAG," or 
something like that. As you can see, I usually use the original 
disk filename, 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 YA 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.YAG 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.YAG, and an 
appropriate label might be "515-27.YAG, scaled from 520-40M.YAG." 
Quit SCALE and call up YA to analyze 515-27.YAG. 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. YA 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 antenna program.

   The output files created for MN, AO or NEC2 will have an 
equivalent diameter 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. 
Such a design with multiple diameter elements will cause YA to 
balk, since it requires a single taper schedule for all elements. 
YA's bigger brother YO will accept such files with no problem, 
however. 

   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 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. 

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

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