After many requests we have created a compact, special balun for Off Center Fed (OCF) and loop (Skyloop or Delta loop) antennas. The CB-4-1-1500 is a CUBE(TM) enclosure containing a multi-core, broadband 4:1 impedance transformer in series with a 1:1 current balun for extra common mode current choking to keep RF current off the outside of the coax braid and on the antenna where it belongs. The extra choking action also means that the coax feed line will not act as a radiator causing unnecessary RF interference (RFI). Rated for full 1500 watts PEP and 450 watts CW (ICAS). 1.8Mhz – 61 MHz.
The CB-4-1-3000(3KW) and CB-4-1-5000 (5KW) versions have a frequency range of 1.8-31 MHz and do not cover 6 meters.
CB-4-1-1500 is housed in a 4” x 4” x 2” waterproof housing with SO-239 input and stainless steel eye bolts on the side for ease of connection to your wire antenna. Top eye bolt acts as an antenna hoist.
3KW and 5KW are in 6" x 6" x 4" enclosure. 1.5KW is 3 pounds, 3KW is 4 pounds, 5KW is 5 pounds.
For OCF antennas we recommend a 21%/79% offset for best all band results. If you use 66%/34% offset, do not use on 15 meters as the impedance mismatch will damage the balun. Loop antennas should be cut for 1005/F(MHz) in total length, where F (MHz) is the lowest frequency to be used. For 3.5MHz this equates to 288 feet.
We highly recommend a feed line choke (MC-1-3000) or coax noise filter (CMNF-1500) at the radio end of the coax feed line to reduce common mode noise picked up by the coax braid.
Callsign: NE5U Your CB-4-1500G5RV +1:1 Choke made my homebrew, hail mary, 3 times folded 75m resonant attic dipole into a functional antenna from 6m to 160m. Most bands I can operate with no RFI. I've installed ferrites at all of the usual locations but still have some problem bands. Considering that the antenna is, at best, an NVIS antenna, I have made a lot of DX contacts (SSB, FT8 and other digital modes, and CW). Happy customer here. 73