Model BA-4-250 is a 4:1 voltage balun/Unun kit (assembly required from parts supplied) used to translate a 50 ohm input up to 200 ohms at power levels up to 250 watts when used with a matched load. With a matched load the SWR will not exceed 2:1 over the frequency range 1.8 to 30 MHz. The kit consists of a 1.4" diameter ferrite core, two colors of insulated wire. a UHF connector with stainless steel hardware, and an instruction manual with directions to connect the kit as a 4 to 1 balun (balanced coax to balanced antenna like zepp or from 450 ohm feeder line to coax for a tuner) or 4 to 1 unun (unbalanced coax to unbalanced antenna like end fed or random wire). This balun will also transform at 4:1 for a wide variation of load impedances. Shown below are AIM 4170 SWR results for a 200 ohm load. This balun gives near perfect transformation through 30 Mhz with a SWR under 1.25 . Light blue vertical bars are ham bands starting at 160 meters at left to 10 meters at right.
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.