1500 Watt Rated 1.5:1 CUBE™ Unun
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.
Testimonial
Hi Bob,
Radio: Flex-6700 running barefoot -10 to 100 Watts max.
Antenna: MFJ-1216 – 160/80 meter OCFD wire antenna with matching network.
Elevation: Over 60 feet AGL – fully extended.
Installed: Mid November 2013
I operate mainly on the digital modes running less than 50 Watts. All of the sudden after a few days operating with this antenna, I start to have RFI and my radio was acting up; such as changing bands, SWR changing values, radio failures and turning off. However, when I used my Hy-Gain 18 HT vertical on the same band none of the abnormality occurred.
I contacted MFJ and confirm that what I was noticing was a failure of their “matching network” AKA balun. They offered no solutions. Then I contacted Palomar Engineers and bought the 1:1 new toroid RF beads. I called Palomar Engineers and I happened to talked to you directly; regarding the on going issue with the MFJ antenna. I found out that the 1:1 balun was not what I needed (I was miss-informed by MFJ that it was 1:1 matching network.)
You offered to make the required balun 4:1 and the rest is history.
Here are my findings:
- No more RFI displayed on the monitors.
- Radio not acting up or turning off.
- The SWR at 160/80 meter is 1.2:1
- No antenna tuner required. (radio goes to Bypass automatically.)
- Worst SWR is on 10 meter with a 2:1 but still usable, with antenna tuner 1.5.
- One happy OCFD user!
Thanks to Palomar Engineers design and engineering for solving this issue.
73, Ernest – W4EG