                Documentation for AAT.EXE Program
                    Ver. 1.0, Mar 10, 1997
                     by R. Dean Straw, N6BV
             Senior Assistant Technical Editor, ARRL

   AAT is a software tool designed to put an antenna tuner 
through a huge battery of tests. The name "AAT" is short for 
"Analyze Antenna Tuner."  AAT uses the same core algorithms as 
the TLA program, but it uses them automatically to evaluate 2,277 
combinations of resistance and reactance in the amateur bands 
from 1.8 to 29.7 MHz. At each impedance, AAT sees if the tuner 
can make a match, while meeting performance criteria set by the 
operator.

USING AAT

   The best way to learn how to use AAT is to actually try it 
out. Let's assume that you want to evaluate a Tee-network on 
the ham bands between 1.8 to 29.7 MHz. 

   First, you need to get into the subdirectory containing 
AAT.EXE, and then you can boot up the program. You do this using 
the CD [change directory] command in DOS. 

   If you have done a standard installation using the INSTALL 
program provided with the diskette in the back of the 18th 
Edition of The ARRL Antenna Book, the default directory for AAT 
is \ANTBOOK\XMSNLINE.

      CD \ANTBOOK\XMSNLINE [Enter]

Now, Type:

      AAT [Enter]

and you will see the AAT's main menu. 


SETUP CHOICES - D (Defaults)

   The Defaults stored in the program represent realistic values 
for typical components, but you may want to change them to 
whatever you like. For example, an unloaded Q of 200 for a roller 
inductor is pretty typical. If the inductor is located very close 
to a metal chassis, however, the unloaded Q can drop as low as 50 
to 75. This induces extra losses in the inductor.

   An unloaded Q of 1000 for an air-variable capacitor with 
wiping contacts is also pretty typical. A vacuum-variable 
capacitor, which has bellows-type contacts, may have an unloaded 
Q of 5000. Even at Qu = 1000, however, the main losses in a tuner 
are not likely to be in the variable capacitors -- they'll still 
be in the coil, because of its lower unloaded Q.

   You may set the power into the tuner from the transmitter to 
whatever you like. The default setting is 1500 W, the maximum 
amateur limit in the USA. 

   You may also change the value of the resistance the tuner is 
striving to achieve at its input when it is tuned properly. For 
example, some designs use a 1:4 autotransformer at the input to 
transform 12.5 ohms at the input of the tuning network to 50 ohms 
for the transmitter. This strategy allows components with 
practical values to be used for certain standard types of marine 
antennas (a 35-foot whip, usually), but it does result in higher 
losses in the tuner than a straightforward 50 ohm resistance at 
the tuner's input.

SETUP CHOICES -- M (Min/Max)

   AAT needs to know the range of capacity in the tuning 
capacitors. AAT assumes that identical capacitors will be used in 
the input and output for Pi-network and Tee-network tuners. AAT 
does allow you to specify a fixed padding capacitor at the output 
to augment the output capacity at 160 and 80 meters. 

   To use the M function in AAT, first, you would want to choose 
suitable variable capacitors for the input and output capacitors. 
Let's assume for your Tee-network tuner that you decide to use 
the popular Johnson 154-16-1, which is rated for a minimum to 
maximum range from 32 to 241 pF, at 4500 V peak. Stray capacity 
in the circuit is estimated at 10 pF, making the actual range 
from 42 to 251 pF. So, you would enter 42 when AAT asks for the 
minimum capacity, and 251 when it asks for the maximum.

   Note: if you decide to use a dual-section type of variable 
capacitor, where you switch in manually one or both sections, 
specify the minimum capacity of one section (plus an estimated 
stray capacity -- usually 10 pF is about right), and enter for 
the maximum capacity the sum of the two sections, plus double the 
stray (about 20 pF typically). For example, if each section of a 
dual-section capacitor ranges from 24 to 191 pF, then you would 
use for the minimum value 24 + 10 = 34 pF, and 191 + 191 + 20 = 
402 pF for the maximum value. 

   The program next asks you if you want to specify a fixed 
capacitor across the output variable capacitor for 160/80 meters. 
If you do want to switch in such a fixed padder capacitor, answer 
"Y" for yes. Then you may specify the value. AAT will only allow 
you to specify a value less than or equal to the maximum capacity 
you entered in the last step. This is so that the tuning range of 
the capacitor with and without the switched-in padder will cover 
a continuous range.

   Next, you choose the maximum inductance for the variable 
inductor to be used in your tuner. Many people use the popular 
Johnson 229-203-1, which has a maximum inductance of 28 
microhenries, and an unloaded Q of at least 200. 

SETUP CHOICES -- P (Power Loss)

   Let's say that you decide to set a power-loss limit of 20%, 
equivalent to a power loss of about 1 dB. Bear in mind that for 
1500 W input to the tuner, you will burn up 300 W of power inside 
for a 20% power loss! Whatever value you enter for percentage  
power loss, AAT will compute and display the equivalent in dB.

SETUP CHOICES -- V (Voltage Limit)

   AAT allows you to specify two different voltage limits for the 
variable capacitors used in a Tee or Pi-network tuner. For the L-
network, a single value for the voltage rating is used. The 
voltage limit you enter is the peak voltage rating, sometimes 
known as the "peak withstanding voltage" on capacitor 
specification sheets.

NETWORK CHOICES 1 TO 4

   AAT's opening menu shows the choices you have to operate the 
program, including the default values stored internally. Hitting 
a number 1 to 4 tells the program to make its calculations for 
the network type you have chosen. AAT will ask you to confirm 
that you really want to go ahead using the values on-screen for 
the components. 

OUTPUT FROM AAT

   After AAT goes through its full range of computations, it will 
exit back to DOS, with two messages: the filenames for the SUM 
and the LOG files it creates, along with the time taken to do its 
computations. The time to do a computation for a Tee-network 
tuner with large variable capacitors and a switched fixed output 
capacitor can seem very long. 

   The first file AAT creates is a summary (TEENET.SUM, in this 
example) and the second is a detailed log (TEENET.LOG) of 
successful matches -- together with matches that came close, 
except for exceeding a voltage rating. Both files are ASCII text 
files, and can be read using a standard word processor.

   As explained in detail in the 18th Edition of The ARRL Antenna 
Book, the numbers in the "matching map" grid represent the power 
loss percentage for each impedance where a match is indeed 
possible. 

   For the Pi-network and the Tee-network, which have three 
variable components, the program varies the output capacitor in 
discreet steps of capacitance. It is possible for AAT to miss 
very critical matching combinations because of the size of the 
steps necessary to hold execution time down. You can sometimes 
find such critical matching points manually using the TLA 
program. 

   On a 100-MHz Pentium, AAT takes almost four minutes to 
evaluate all 2,277 combinations for the default component values. 
On a 33-MHz '486DX machine it really seems to crawl. Because of 
such execution-time considerations, AAT does an extensive search, 
but not an exhaustive one.

   AAT produces similar tables for Pi-network and L-network 
configurations, mapping the matching capabilities for the 
component combinations chosen. All computations are, of course, 
only as accurate as the assumed values for unloaded Qu in the 
components. The unloaded Qu of variable inductors can vary quite 
a bit over the full amateur MF and HF frequency range. 

   In general, L-networks will exhibit the least loss among the 
various network configurations, but they often require awkward 
values for inductance and capacitance. The Tee-network 
configuration is often used because it can accommodate a wider 
range of impedances with practical values of variable capacitors 
and inductors, albeit with sometimes disastrous internal losses. 
The Pi-network configuration is flexible, but it too will often 
require very large values for capacitors. 

   Computations produced by AAT have been compared to measured 
results on real antenna tuners and they correlate well when 
measured values for unloaded inductor Qu are plugged into AAT. 
Individual antenna tuners may well vary, depending on what sort 
of stray inductance or capacitance is introduced during 
construction. 

EXITING CLEANLY

   AAT displays everything in color. If for some reason you use 
<Ctrl>C or <Ctrl>Break to exit the program, you will be left in 
DOS, with a messy blue background. Either type CLS [Enter] or 
MODE=CO80 [Enter] to restore the screen to normal.
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