Auto .nec input file generator

#1
Hello,

I've been experimenting with Franklin co-linear antennas made up from 14 gauge single strand
copper ( from scraps of stripped 14-2 electrical wire ). I'm getting a range of just over
100 mile radius with the antenna strapped to a broom handle about 6 feet off the ground,
using the RTL-SDR usb module and dump1090 driver.

The dimensions for my best effort are: 137mm verticals, 67mm stub lengths spaced at 10mm
with both 75 ohm co-ax feed and 110mm co-ax half wave balun connected on the central stub
20mm away from the vertical sections.

I've been using xnec2c modeling software and I've noticed many of the dimensions can
have a critical effect on gain and VSWR so it's necessary to make many nec runs,
editing the input file to change various dimensions each time. I wrote a simple python script
that automatically creates the NEC input text files, making a simple job of repeatedly making up
antenna files with different trial dimensions.
Here's the python script in case anyone else can use it:
( You will need to change the filetype back from .txt to .py after downloading)
 

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#2
The dimensions for my best effort are: 137mm verticals, 67mm stub lengths spaced at 10mm
with both 75 ohm co-ax feed and 110mm co-ax half wave balun connected on the central stub
20mm away from the vertical sections.
I love your nic !!

Any chance of a picture of your antenna? I've settled on a 6 element Franklin as my standard. It gives the best results for my location ~200nm on a good day. It is 15m above ground.

Thanks for the Python code too
 
#3
Thanks !
here's a pic, you can tell it's not rooftop ready yet. The dimensions are a little different from my 'best' viz:
vert=127mm, hori=66mm hgap=4mm stub=58mm sgap=4mm diam=1.6mm
xnec2c program tells me these dimensions should give gain=7.9db and VSWR=1.4 .
So far it performs _nearly_ as well as my best, dimensions in the first post, which theoretically has
gain=7.5db and VSWR=3.2 ( Both are feeding 75ohm coax )
I'd like to better understand what the program is telling me before I go climbing.
yw on the script, it could be easily extended for six elements.
Best
 

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