Yagi-Uda project first

first makes an attempt to design an antenna, very roughly based on the ideas of DL6WU.

The manual page  first.1  describes all the options of first. The manual page first.5 describes the file format for first. However, it is better to read this page before looking at the man pages.

The DL6WU designs are only valid for more than 10 elements, but this does not matter here, as the design will be optimised later. The antenna will have one driven element, one reflector and 0 or more directors.

parrot /export/home/drkirkby/yagiuda-1.18/src % first
Yagi-Uda antenna analysis programs, version 1.12
Written by Dr. David Kirkby Ph.D. G8WRB (email:drkirkby@kirkbymicrowave.co.uk)
Usage: first filename elements min_f f max_f step_f diameter
       where frequencies are in MHz and diameter is in mm
'first' is used to define an antenna quickly, according to DL6WU designs.
It is much faster in use than 'input'
Example: first 145e20 20 144 145 146 .1 6.3

will make a file '145e20' containing a description of a 20 element DL6WU yagi,
for 144-146 MHz, designed at 145MHz, which 'yagi' will calculate in steps of
0.1MHz. The antenna uses 6.3mm diameter elements.

We will now show an example of the use of first. In this example a 5 elemant antenna is designed for 145 MHz, but will be analysed over the range 144- 146 MHz, in steps of 100 kHz.

parrot /export/home/drkirkby/yagiuda-1.18/src % first example1 5 144 145 146 0.1 5
DL6WU antennas are only valid for 10 or more elements, but I'll do it!

Now, we will look at the output file created. Note comments begin with a #, all elements have y = 0, indicating they are on the same axis. The position of the reflector is at x=0, and the driven element and all directors at x > 0. In this example, the  reflector  is 1.00537 m long, placed at x=0. The driven element is 0.97115 m long, and placed at 0.41379 m in front of the reflector. The first director is placed 0.56897 m in front of the reflector and the so on. Note the reflector is the longest element ( 1.00537 m), the driven element the second longest and the elements get shorter towards the front on the antenna.

parrot /export/home/drkirkby/yagiuda-1.18/src % cat example1
NOTES Automatically produced by first
FREQUENCY 145.000000
MIN_FREQUENCY 144.000000
MAX_FREQUENCY 146.000000
ANGULAR_STEP   180.000000
#DATA_DRIVEN        x         y       length     diameter voltage(r) voltage(i)
DATA_DRIVEN     0.41379    0.00000    0.97115    0.00500    1.00000    0.00000
#DATA_PARASITIC     x         y       length     diameter
                0.00000    0.00000    1.00537    0.00500 reflector
                0.56897    0.00000    0.92787    0.00500 D1
                0.94138    0.00000    0.92098    0.00500 D2
                1.38621    0.00000    0.91272    0.00500 D3
parrot /export/home/drkirkby/yagiuda-1.18/src %

In order to analyse this antenna, we use another programme called yagi.