Model CU-9-5000 is a 9:1, multi-core unun housed in a NEMA enclosure box (4″ x 4″ x 2″) with top stud output and side stud (counterpoise) used to translate a 50 ohm input up to 450 ohms unbalanced at RF power levels up to 5 KW PEP/ 1.5KW continuous when used with a matched 450 ohm load. With a matched 450 ohm load the SWR over the frequency range 1.8 to 31 MHz is less than 2:1 on the coax feed side. SO-239 input/(N input optional) and top/side eyebolt/wing nuts output.

Great for end fed antennas - FT-8 and digital mode power ratings are approximately 30% of PEP ratings into a matched 450 ohm load. For non-resonant end fed antennas, you will need a feed line choke on the coax. See typical antenna configuration notes below for details.

Application

For end fed, traveling wave and certain types of telescoping vertical antennas, the 9:1 unun makes a good transformer for converting to unbalanced 50 ohm coax to the unbalanced 450 ohm antenna feed point.If you use the antenna on multiple bands, the feedpoint impedance may not always be 450 ohms and use of the balun at high (>600 ohms) or low (<300) may require reduced power input or the balun/unun may have its power ratings exceeded and damage to the balun may occur. The (9:1 conversion ratio will change for loads other than 450 ohms unbalanced). Tech Note: The RF output and the counterpoise/coax shield are DC shorted.

Suggested wire lengths (measured from antenna wire connection at top of CU-9-1500, 5000):

General Notes

For antennas over 71 feet, use 100 feet coax minimum and place choke in a position as shown in table below.This choke position will be a good starting point for tuning your antenna on the bands you want to operate.Here are some examples of actual antenna wire length and choke placement for the antenna SWR plots shown (units are in feet and % of total antenna length including counterpoise):

If you intend to use this impedance transformer for end fed wire antennas using the coax as a counterpoise we recommend the following antenna length:

(*) - Choke measurement is from antenna feed point at 9:1 unun coax connector to choke.

DO NOY TRY TO FEED BALANCED LOADS (E.G. LADDER LINE FED ANTENNAS) BY USING THE SIDE TERMINAL OF THE OUTPUT AS SERIOUS DAMAGE TO THE UNUN MAY OCCUR

Choke & Impedance Transformer Power Rating Table

The table below attempts to generalize the power rating of various chokes and impedance transformers manufactured by Palomar Engineers. These rating do not apply to other manufacturers. (We have replaced many failures of other manufacturers who rate impedance transformers for 1500 watts PEP but fail at 250 watts CW in a high duty (contest operation or digital mode) use. This failure is quite common for End Fed 9:1, 49:1 and OCF 4:1 baluns used for contesting or high duty digital modes at high power as the transformer is under engineered for the wide range of impedances encountered over the antenna range. (Note: a simple test to determine the quality of the impedance transformer or choke is to weigh it – most high power (>1500 watts PEP) devices will weigh between 1-3 pounds as that is the weight of typical ferrite materials that is required for proper operation over a wide frequency range). Don’t expect a wimpy 1/2 pound OCF balun to take a 1500 watt PEP signal for long! When your OCF balun fails, check out our OCF Baluns.

The ratings in the table assume a resistive load (SWR = 1:1) within the frequency range specified for the choke or transformer. Check the product specifications for each model as certain models have specific frequency ranges, impedance min/max, and power ratings. Measure the SWR without an antenna tuner (that’s what the balun/unun sees as it load) and for SWR other than 1:1, divide the rating shown in the table below by (square root of swr). E.g. if SWR is 5:1, the square root of 5 = 2.24 so a 1.5KW PEP SSB 50% rated transformer should be limited to 1500/2.24 = 670 watts max PEP SSB 50% input. For SWR = 3:1, square root is 1.73, so 1500/1.73 = 867 watts max SSB 50%, 2:1 square root is 1.414 so 1500/1.414 = 1061 watts SSB 50% or 469/1.414 = 332 watts AM/FM/Digital continuous.

Note: FT8 = Continuous Carrier – 50% on/off. 1500 Watts balun has FT8 rating of 656 watts at 1:1. At 2:1 max would be 656/1.414 = 468 watts input. For 5000 watts balun, FT8 is 2,188 watts at 1:1 and at 2:1 SWR (no tuner), FT8 max input is 2188/1.414 = 1,547 watts.