## Shorty 40 analysis

A Shorty 40 is a shortened 40 meter dipole which uses a matching transformer/loading coil consisting of a 30 turn coil of AWG 12 wire on a 2.5" diameter form 6" long. The elements are typically 18'6" long (on either side of the center) for a total length of about 11.3 meters.

Using the program ACMI from Paul Nicholson (http://www.abelian.demon.co.uk/acmi/) , we can calculate self and mutual impedances for the coils. Of course, that program does NOT calculate the stray capacitances, which are significant. The coils were modeled as 3 windings:

 tapped at 2 turns tapped at 3 turns feed L (uH) 0.46 0.90 feed R 0 0 sec 1 L (uH) 7.95 7.13 sec 1 R 0.01 0.01 sec 2 L (uH) 9.61 9.61 sec 2 R 0.02 0.02 M Feed:sec1 (uH) 0.57 0.75 k .2981 .2970 M feed: sec 2 (uH) 0.59 0.79 k .2788 .2685 M sec 1: sec 2 (uH) 1.10 0.90 k .1255 .1082

Input file for ACMI

```; Shorty 40 matching coil
; 6 tpi, 30 turns on 5" long 2.5" diam form
;
; A closely coupled helical impedance matching transformer

feed {

height1  0.0
height2  3/6*0.0254

conductor  12 awg  ; wire radius
turns 3
}

sec1 {

radius 0.03175		; 2.5 inch diam

height1 3/6*0.0254
height2 0.0635

conductor 12 awg
turns 12
}

sec2 {

radius 0.03175		; 2.5 inch diam

height1 -0.0635
height2 0.0

conductor 12 awg
turns 15
}

```

ACMI output

```2 turns
FD.L|   FD.R|     SC1.L|  SC1.R|     SC2.L|  SC2.R|   FD-SC1.M|   FD-SC1.K
|   FD-SC2.M|   FD-SC2.K|  SC1-SC2.M|  SC1-SC2.K
0.46 uH|   0.00|   7.95 uH|   0.01|   9.61 uH|   0.02|    0.57 uH|     0.2981
|    0.59 uH|     0.2788|    1.10 uH|     0.1255
3 turns
FD.L|   FD.R|     SC1.L|  SC1.R|     SC2.L|  SC2.R|   FD-SC1.M|   FD-SC1.K
|   FD-SC2.M|   FD-SC2.K|  SC1-SC2.M|  SC1-SC2.K
0.90 uH|   0.00|   7.13 uH|   0.01|   9.61 uH|   0.02|    0.75 uH|     0.2970
|    0.79 uH|     0.2685|    0.90 uH|     0.1082

```

Here's a NEC analysis of the antenna itself, with the feed point impedances..
CE
GW 1 41 0 -5.716 0 0 5.716 0 .001
GE 0
EX 0 1 21 0 1 0
FR 0 1 0 0 7.2 1

```F	R	X
6.90	15.08	-837.11
6.95	15.33	-826.76
7.00	15.58	-816.51
7.05	15.83	-806.37
7.10	16.09	-796.33
7.15	16.35	-786.40
7.20	16.61	-776.57
7.25	16.87	-766.83
7.30	17.14	-757.19
7.35	17.41	-747.65
7.40	17.68	-738.19
7.45	17.96	-728.83
7.50	18.24	-719.55

```

An inductively loaded 80m Yagi: http://www.qsl.net/ve6wz/intro.htm

radio/antenna/s40.htm - 30 Jan 2003 - Jim Lux