Baluns, chokes, line isolators for dipoles, verticals, beams, slopers, loops

Keeping the RF on the antenna and off the coax feed line.

1. Match the coax impedance to the feed point impedance using an impedance transformer( balun or unun).

For dipoles between .25 to .4 wavelength height over RF ground the feed point impedance is 100 ohms and a 2:1 balun is best used.  If the antenna is less than 1/3 wavelength or higher than 1/2 wavelength the impedance is closer to 75 ohms and a 1:1 current balun is sufficient.  Choose the power needed and the form desired.  A simple sleeve balun works in most cases but for additional choking protection use a CUBE™ balun in a weather proof box or for general use our Super Choker™.  Click DIPOLE ANTENNAS for more height info.

For verticals or slopers use a 9:1 (long wire) or 4:1 (31-43 foot verticals over 10 Mhz) or 1:1 unun (1/4 wave verticals)  AND a 1:1 feed line choke to keep the coax line from radiating.  the CUBE™ impedance transformer is the best for this application or simple-to-wind kits are also available.  Choose 9:1, 4:1 or 1:1 kits at the appropriate power level desired.

For loop antennas, the feed point is usually 100 ohms so a 2:1 balun is used – choose 2:1 at appropriate power level.  Kits and assembled version available.

For beam antennas, choose sleeve choke or CUBE™ choke at appropriate power level.

For OCF (off center fed) use a 4:1 current balun or our special CB-4-1500OCF, 4:1 OCF balun with built in 4:1 balun AND 1:1 unun in a weatherproof box.

Keeping common mode feed line current out of the radio

While the feedline choke at the antenna feed point keeps transmitted RF off the feed line, the radiated RF from the antenna AND common mode current induced by other radiated sources (plasma TV, routers, etc) can be picked up by the outside of the coax braid from the antenna feed point back to the radio transmitter/receiver.  This portion of the coax braid now acts like a receiving antenna, picking up common mode noise an wreaking havoc with weak signals!

The solution?  Another common mode choke with high choking impedance at the radio end of the coax.  We suggest the 1:1 CUBE™ choke with SO-239 connectors in and out which just connect inline after your antenna tuner, effectively reducing common mode noise.  ALL antenna lines entering the radio room need to have a 1:1 balun on the coax unless fed by a common coax switch.  Choking only 1 line if you have 5 antenna coax feeds will do little good – you need to choke all five – use the sleeve chokes  (with lower choking impedance) if cost is a concern.

Typical chokes used at antenna feed point or at entrance to station (click on picture for product info)

CUBE Choke – 1:1 SO239 or side stud output	Super Choker 4010 – 40-10 meters
FC1 Feed Line Choke – 1 to 61 Mhz	SNAP On Sleeve Baluns for 1/4″, 1/2″, 1″ cable