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 2.4″ OD/1.4″ ID ring toroids as follows:
Mix 75 effective from .15-10 MHz including AM Broadcast band – quantity: 3
Mix 31 effective from 1-300 MHz for general purpose – quantity: 4
Mix 61 effective from 200-2000 MHz for cell phone, WIFI, HDTV, Cable TV interference – quantity: 3
Feed Line Choke
Each end fed antenna needs a feed line
choke at the radio end of the coax to stop the antenna common mode
current (on the coax braid) from getting into the radio when
transmitting and also to stop RFI common mode noise when receiving. The
simplest, most cost effective choke is a ferrite ring (F240 size)
installed as shown in the picture (at the transceiver end of the coax)
Add the Feed line choke (part # EFFLC-240) for $10 to your end fed
today and stop the pesky RFI from getting into your radio and causing
audio distortion or unexpected operation!
NOTE: Coax shown in picture is NOT INCLUDED and is shown as an installation example only. If you want a pre-wound choke check part# JC-1-1500-3 or JC-1-1500-6.
For non-resonant end fed antennas placement of the choke from 16-95 feet away from the antenna feed point to use the coax braid as the counterpoise (since these antennas are really off center fed dipoles with the short side using the coax braid as the counterpoise. Wind 8-10 turns thru center for an effective 3-30 MHz choke. See Bullet Antenna configurations for exact choke placement depending upon wire length.
For End fed Half Wave antennas place 1-3 feet from antenna feed point to act as short counterpoise for these voltage fed antennas. Use 8-10 turns.
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).