Palomar Engineers RFI Filter Kit for CB Radio Radio Transceivers from 20-30 MHz uses ferrite rings for the DC power supply and the coax to the antenna. BUY THIS KIT NOW TO SOLVE YOUR RFI/EMI NEEDS! WORKS WITH ALL BRANDS (Cobra, DAS, Midland, Uniden etc.) OF CB/HAM/COMMERCIAL RADIO RIGS in 20-60 MHz range. Purpose The RFI kit is designed to be installed on your radio transceiver to reduce Radio Frequency Interference (RFI) caused by common mode current on the outside of the coax braid at the output of your radio and on the DC power supply cable. This kit will help reduce or eliminate: 1. “Hot mic” RFI caused by poor grounding of antennas or common mode currents from linear amps feeding unbalanced (coax fed) antennas without baluns/line isolators. 2. RFI to neighbor’s electronic devices including audio/video systems, computers, telephones, garage door openers, etc. 3. RFI to your other radios, audio/video systems, computers, telephones, etc. A side benefit is a reduction in noise floor in your receiver depending on the amount of noise being introduced by common mode currents (which are blocked/reduced by the chokes in this kit). These chokes use a special mix of ferrite core material that is effective in suppressing radio frequency interference from Ham Radio amplifiers. Included are the following chokes and installation guidelines: DC Input: F240 Ring – 3-7 turns of DC power cable - sized for smaller plugs RF Input/Output: F240-31 ring - wrap 6 turns of RG8X size cable near the back of the radio For additional RFI suppression, use a MC-1-500-50 mini feed line choke at the antenna feed point to suppress common current on the coax feed line during transmit and a CMNF-500-50 Coax Noise Filter to reduce common mode noise during receive operations. If you use a switching power supply for base operation, consider the RFI-SMPS switching power supply RFI kit. If you use a linear amplifier we have RFI kits for linear amplifiers that help suppress RFI in your shack or in your neighbor’s house.
Iron powder cores are more stable than ferrites and do not saturate as easily so they are best for tuned circuits, filters, and high power inductors. They come in different “Mixes” for use at different frequencies. For best “Q” use the Mix specified for your frequency.To find the number of turns to give the desired inductance for your coil use the formula below:
Turns = 100 x 
Toroid Dimensions
To order specify core size and mix (e.g. T200A-2). Available in sizes that have µH per 100 turns shown in table.
All iron powder cores are special orders. Please allow one week for shipment after order received.
The iron powder cores shown in the above tables are primarily used for either high power feed line chokes for common mode current reduction or for 4:1 and 9;1 very high power transmission line transformers.
For high power feed line chokes, choose the inside diameter of the iron powder core closest to the transmission line outside diameter and use 6-20 cores at the junction with the antenna feed.
For 4:1 (50/200 or 75/300 ohm) transmission line transformers in the range of 1.8-30 Mhz, select the size appropriate for the power level as follows:
T200A x 2 = 1.5KW
T300A x 2 = 2.5KW
T400A x 2 = 5KW
Use Mix 2 for all the above transmission line transformers. Fully assembled and enclosed units are available for each of the power levels. Click HERE for information.
4:1 transmission line transformers using iron powder cores are typically used for ladder line to 50 ohm coax connections
For .1 – 2 Mhz wide band transformers use Mix 26 which has a higher permeability and requires less turns to achieve a given inductance. Mix 2 has almost constant permeability from 1-30 Mhz. Mix 26 has an initial permeability of 75 at .1 Mhz and gradually decreases to about 10 at 30 Mhz. For high power AM broadcast range (.5-1.7 Mhz) transformer, use Mix 26 to reduce the turn count.
Minimum order for iron powder cores is $50
Shipping on larger cores in quantity may be more than $10 – email/call for quote.