Prime focus parabolic dish focus, gain and beamwidth calculator for HP41C

Messy stack version by Michael Fletcher, OH2AUE, 1999
Minor cosmetic improvements, 2005 (yes, I am still using this !)

G_ant = 4 * π * A_e /λ₀²         A_e = h * A            A = π * r²                Θ_E (-3dB) = (73 * λ₀) / D
 
A_e = effective aperture of dish
h = illumination efficiency
λ₀ = freespace wavelength
π = pi
Θ_E (-3dB) = electrical field half power beamwidth

a = (d * f) / D - (d * D)/(16 * f)                  a = focal point inside horn
                                                                  D = dish diameter
                                                                  d = feed waveguide aperture diameter (without scalar ring)
                                                                  f = dish focal length (prime focus)
 

1 LBL GAIN                     ( f LBL alpha GAIN alpha )
2 ANT DIA CM ?             ( alpha ANT DIA, CM ? Alpha )
3 PROMPT                       ( XEQ alpha PROMPT alpha )
4 STO 01                           ( Prime focus dish diameter )
5 TONE 9                          ( XEQ alpha TONE alpha 5 )
6 FREQ GHZ ?
7 PROMPT
8 STO 02
9 TONE 9
10 EFF O,XX ?
11 PROMPT
12 STO 03                          ( Prime focus dish aperture efficiency )
13 TONE 9
14 RCL 01
15 2
16 /
17 x²
18 PI
19 *
20 RCL 03
21 *
22 4
23 *
24 PI
25 *
26 30
27 RCL 02
28 /
29 STO 05                           ( λ₀ in cm )
30 x²
31 /
32 LOG
33 10
34 *
35 TONE 5
36 FIX 1
37  STO 04                         ( Dish gain in dBi )
38  GAIN, DB=
39 ARCL 04
40  AVIEW
41 STOP
42 RCL 05
43 RCL 01
44 /
45 73
46 *
47 FIX 2
48 STO 06                           ( Dish E_-3dB beamwidth )
49 TONE 5
50 BW, DEG=
51 ARCL 06
52 AVIEW
53 STOP
54 FEED DIA, CM?
55 PROMPT
56 STO 07                           ( Prime focus dish feedhorn waveguide aperture diameter )
57 TONE 9
58 DISH FL, CM?
59 PROMPT
60 STO 08                           ( Antenna dish focal length )
61 RCL 07
62 RCL 08
63 *
64 RCL 01
65 /
66 RCL 07
67 RCL 01
68 *
69 16
70 /
71 RCL 08
72 /
73 -
74 STO 09                            ( Focal point inside horn )
75 FIX 1
76 TONE 5
77 F. IN HORN, CM=
78  ARCL 09
79 AVIEW
80 RTN