raek

Common Mode Choke (Balun)

In this article I dive into the common mode choke of my attic antenna presented in the previous post.

Why do you need a common mode choke (or "balun")? A coaxial cable has two spaces: the inside (everything between the shield and the center conductor) and the outside (everything outide the shield). The shield is the wall between these spaces. Electromagnetic waves propagate along the coaxial cable both on the

What does a common mode choke / balun do in this context? It is a lossy inductor that only affects common mode currents flowing on the outside of the coax.

The design is pretty standard: 13 turns (6 turns, one crossover, and 6 more turns) of RG316 coax around a FT240-43 core. To evaluate it, I made a small jig to perform a "S21 series measurement".

raek

import weechat as w


morse = {
    "0" : "-----",
    "1" : ".----",
    "2" : "..---",
    "3" : "...--",
    "4" : "....-",
    "5" : ".....",

raek

import collections
import re
import sys


ends = collections.Counter()
paths = collections.Counter()

def clean(path):
    parts = path.split(",")

raek

Here is a video I like:

.. youtube:: I2Q35uFCq8Q

Neat, huh?

raek

---
- name: Install Pladder
  hosts: all
  tasks:
    - name: Install system dependencies
      become: yes
      apt:
        pkg:
        - build-essential
        - pkg-config

raek

             position: 39 of 3683 (1%), column: 0
            character: i (displayed as i) (codepoint 105, #o151, #x69)                                                                                                                                                                                     charset: ascii (ASCII (ISO646 IRV))
code point in charset: 0x69                                                                                                                                                                                                                                 script: latin                                                                                                                                                                                                                                syntax: w        which means: word
             category: .:Base, L:Left-to-right (strong), a:ASCII, l:Latin, r:Roman
             to input: type "C-x 8 RET 69" or "C-x 8 RET LATIN SMALL LETTER I"
 

raek

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

int main(int argc, char **argv)
{
    DDRD |= 1<<0;
    PORTD |= 1<<0;
    _delay_ms(500);
    PORTD &= ~(1<<0);

raek

demo_blinky.avr.elf:     file format elf32-avr


Disassembly of section .text:

00000000 <__vectors>:
   0:	0c 94 56 00 	jmp	0xac	; 0xac <__ctors_end>
   4:	0c 94 60 00 	jmp	0xc0	; 0xc0 <__bad_interrupt>
   8:	0c 94 60 00 	jmp	0xc0	; 0xc0 <__bad_interrupt>

raek

raek@mizar:~/src/cffi$ source .venv/bin/activate
(.venv) raek@mizar:~/src/cffi$ hg --verbose push --new-branch -r doc-improvements
pushing to ssh://[email protected]/pypy/cffi
Enter passphrase for key '/home/raek/.ssh/id_rsa': 
searching for changes
5 changesets found
uncompressed size of bundle content:
    2277 (changelog)
    1441 (manifests)
     405  doc/source/cdef.rst

raek

raek@mizar:~/src/cffi$ hg --verbose push --new-branch -r doc-improvements
pushing to ssh://[email protected]/pypy/cffi
Enter passphrase for key '/home/raek/.ssh/id_rsa': 
searching for changes
5 changesets found
uncompressed size of bundle content:
    2277 (changelog)
    1441 (manifests)
     405  doc/source/cdef.rst
     144  doc/source/index.rst