Linear Amplifier RFI Kits
LINEAR AMPLIFIER RFI KITS
Palomar Engineers has RFI kits for many brand specific linear amplifiers as well as generic RFI kits for both AC powered and DC powered linear amplifiers.
Purpose. These kits are designed to choke common mode currents going into or exiting from your rig. Chokes are supplied for the RF In, RF Out, Relay Cable, and AC/DC power line. Use of the chokes often helps cure high SWR problems between exciter and power rig or between power rig and antenna tuner or direct to antenna. The AC/DC power line choke helps keep common mode current out of the power line which could cause interference to other devices connected to the same power line if not suppressed.
AM broadcast transmits on a low frequency with large antennas. Consequently it takes a large antenna to receive the signals. Typical “antennas” are AC house wiring, phone lines, long satellite or cable TV cables, DSL/CAT5 lines running between rooms, etc. The device wires that connect to these “antennas” need to be choked with as many turns through the ferrite as possible. Some installation examples are shown below on this page.
For AC/ DC power cords and coax cables the F240-77 (2.4″ OD, 1.4″ ID) “Donut” toroid is the most popular. Also available are smaller toroid donuts and Mix 77 beads. Shown below is a graph with 8, 10, and 12 turns through the toroid – obviously more turns has higher choking impedance. Mix 77 toroid products are HERE and Mix 77 small beads (for small wires) are HERE
F240-77 Turns Comparison from .1 – 8.1 Mhz
Shown below is a graph of frequency response verses choking magnitude for a F240-77 in the AM Broadcast band for a 12 turn coil around the toroid. (Same info as above but different frequency range).
F240-77 Choking Impedance in AM Broadcast Band
Typical Installations for Donut/Ring Toroids
 AC Cable on F-240 Toroid – 6 turns |
 Ethernet Cable on F-240 Toroid – 7 turns |
 Audio or Mic cable on F240- 12 turns |
Extra Mix 75 Snap On Beads HERE – VERY effective for AM Broadcast RFI