Iron Powder Cores

HF Transceiver RFI/Noise Reduction Kit, RFI Range 1-300 MHz, 5 Filters

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Product Details


Standard Kit Includes noise reduction ring filters for coax, AC/DC power and 3 snap on filters for I/O cables covering RFI range of 1-300 MHz. Quick installation - immediate RFI/noise reduction. No radio mods required.

Use With all brands including:

Icom: IC-706, 718, 746. 756, 7100, 7200, 7300, 7400

Kenwood: TS-480, 570, 590

Yaesu: FT-450, 817/818, 857, 891, 897, 950, 991A, 1200

If you have a high end radio with multiple antennas, and more than 3 I/O cables, use our Deluxe Transceiver RFI Kit, RFI-XCVR-DELUXE


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 AC/DC power cable. Additional chokes are included to reduce common mode currents on 3 more transceiver cables including computer control, audio and another.

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 transmitters and high noise floor on receivers.

The snap on beads are easy to use, don’t require modification of the protected equipment and work in almost all cases, even when plug-in filters fail.

Use of the chokes often helps cure SWR problems between transceiver and a linear amp and between transceiver 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.

Included are the following chokes and installation guidelines:

RF Input/Output: 1.4" ID ring filter – 5-9 turns of RG-58/RG-8X size coax cable through center

AC/DC Input: 1.4" ID ring filter – 3-7 turns of AC/DC power cable through center

3 additional I/O cables - 1/2" snap on with 1-2 turns through center. Multiple wires can share the same filter.

For additional RFI suppression, use a feed line choke at the antenna feed point to suppress common current on the coax feed line.

If you use a linear amplifier use an amplifier RFI kit for additional RFI interference suppression.

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Iron Cores 150x150 - Iron Powder CoresIron 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 iron core formula 300x14 - Iron Powder Cores

Toroid Dimensions

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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.