Iron Powder Cores

Does the operation of a treadmill or your exercise equipment wipe out your radio receiver reception? We have heard cases where the treadmill from a neighbor’s house wiped out the ham radio receiver reception from 2-30 Mhz! The treadmill source was finally isolated to a variable speed motor power supply that was injecting RFI into the AC wiring of the house and the AC wiring was acting as a transmitting antenna broadcasting the signal to the entire neighborhood. The case was difficult to track down since the broadband RFI interference only occurred at 7-8 pm each nite when the neighbor used the treadmill. As with all RFI cases the sequence is similar: Find the Source, Choke the Path, Protect the Victim.

Once the source was identified, a simple solution was to choke off the transmitting antenna with a AC line choke shown below which eliminated the interference problem to the ham receiver:


FB400-31 AC Power Cord Choke completely cured the RFI problem I had with my wife’s treadmill. Now I can hear the weak signals!

Icom IC-725
Grottoes, Shenandoah Valley, Virginia

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

tcolorcode - Iron Powder Corestcore - Iron Powder Cores


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.