The simplest, most cost effective feed line choke is a ferrite ring installed as shown in the picture (at the antenna feed point) to stop feed line radiation or at the radio end of the coax to suppress common mode coax noise current on the coax braid.
Great choke for log periodics, HF beams, Transceiver/Amp isolation
Improves antenna pattern by preventing your dipole from becoming a tripole
Suppresses pesky coax braid radiation and RFI
Reduces coax braid common mode current up to -40 dB ( 6 “S” units) on receive
Use one choke for each antenna feed line
Add a double female barrel connector to act as an “extension” of the existing coax.
Ferrite Ring Combo Pack, FT140 - .9" ID, 15 Rings - Mix 43, 61, 77, RFI Range .1-2000 MHz
The Ferrite Ring Combo Pack is a convenient solution for troubleshooting RFI/EMI from unknown frequencies or multiple frequencies that require multiple suppression mixes. Included in this combo pack are ten 1.4″ OD/.9″ ID ring toroids as follows:
Mix 77 effective from .1-50 MHz including AM Broadcast band – quantity: 5
Mix 43 effective from 25-250 MHz for general purpose – quantity: 5
Mix 61 effective from 200-2000 MHz for cell phone, WIFI, HDTV, Cable TV interference – quantity: 5
The ring toroids are useful for AC/DC common mode choking with multiple turns as shown below
AC Cable on F-240 Toroid – 7 turns |
DC Cable on F240 – 4 turns |
The ring toroids can also be used on coax or signal lines as shown below:
RG58 12 turns on FT240 |
Ethernet Cable on F-240 Toroid – 7 turns |
For RFI/EMI wrap as many turns as possible for higher choking (under 30 MHz). For over 30 MHz, 1-3 turns is usually sufficient due the to capacitive effect of multiple turns reducing choking effect.