Purpose. This unun is designed to match 250 ohms unbalanced to 50 ohms unbalanced up to 1500 watts PEP power from 1.8-61 MHz. It provides conversion from unbalanced 50 ohm coax to an unbalanced 250 ohm load/antenna feed point and gives a 5:1 impedance step-up to reduce VSWR on the coax feed line. The unun is housed in a 4” x 4” X “2 NEMA weather resistant box with SO-239 coaxial input and a ¼” stud terminal with wing nut on the top for output and another on the side for ground or counterpoise connection. This unun is DC grounded and will bleed off static electricity but it is NOT A LIGHTNING ARRESTOR. Model CU-5-1500 is a 50 ohm to 250 ohm (5:1) voltage unun used to translate a 50 ohm input up to 250 ohms at RF power levels up to 1500 watts PEP (30% duty cycle) when used with a matched load. With a matched 250 ohm unbalanced load SWR should not exceed 2.0 over the frequency range 1.8-61 MHz. Application. For traveling wave, end fed or portable 20-31 foot vertical antennas the 5:1 balun makes a good transformer for converting 50 ohm coax to a 250 ohm feed point. If you use the antenna on multiple bands, the feed point impedance may not always be 250 ohms and use of the unun at high (>350 ohms) or low (<100 ohms) will require reduced power input or the unun may have its power ratings exceeded and damage to the unun may occur. The (5:1 conversion ratio will change for loads other than 250 ohms unbalanced. Typical Antenna System Using CU-5-1500 Use a coax noise filter to reduce noise from any vertical antenna or a line isolator to suppress coax cable braid radiation on transmit.50:250 ohm (5:1) CUBE™ Unun™, 1.8-61 Mz, 1500 Watts, end fed, vertical
Model CU-5-1500EB- 5 to 1 Unun
(SO-239 in/Eye bolt hoist with output connector on top, side stud for ground/counterpoise)
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.