Purpose. The CU-1.5-1500 (1500 watts PEP) or CU-1.5-5000 (5KW PEP) is used as a 1:1 unun(aka feed line choke, line isolator) for 50 ohm unbalanced coax cable input to 75 ohm unbalanced coax output at full amateur radio legal power (1500/5000-watts PEP) into a matched load 50 ohm load for 1.8-61 MHz (or a balanced output load for the CB-1.5-1500/5000). The unun (or balun) is designed to have a high RF impedance to common mode currents on the outside of the coax braid while passing RF currents on the inside of the coax braid to the antenna. For maximum common mode current protection (and receiver noise floor reduction due to common mode current pickup by the coaxial braid), use one feed line choke such as the CU-1-1500 (for 50 ohms coax) or CU-1.5-1500/5000 (for 75 ohm coax) at the antenna and another at the radio shack equipment connection or input of antenna tuner.In some difficult RFI cases, additional common mode chokes are needed between equipment such as linear amps and antenna tuners, and transceivers. This Unun or Balun designed to work with 75 ohm loads and the Unun/Balun will be damaged if you use at high impedances and high power such as driving a 40 meter antenna with an 80 meter transmitter signal where the load impedance on the antenna is very high.Best use is with antennas having a load impedance near 75 ohm range.
1500 Watt Rated 1.5:1 CUBE™ Unun
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.