What is an antenna choke?
A choke ring antenna is a particular form of omnidirectional antenna for use at high frequencies (VHF & UHF). It consists of a number of conductive concentric cylinders around a central antenna.
Do I need a choke balun?
Yes, a balun is needed. All balanced antennas such as dipoles, Yagis and hexbeams that are fed with unbalanced feed lines such as coax, require a choke balun. Without a choke balun, common mode RF currents flow on the outside of the coax making the feedline act like another antenna.
Is a balun the same as a choke?
A 1:1 balun is a transformer, which also blocks cmc (common mode current). A balun choke is not a transformer, it passes current without magnetic intermediate. It only chokes (blocks) cmc.
What is a common mode choke?
A common mode choke is where both line and neutral windings are wound on a single core. When using a current compensated choke to decrease common mode noise, (the interference pattern or the unwanted noise) you want to have a high impedance at the unwanted frequencies to knock down that unwanted noise.
Why are baluns used?
Baluns are used both to sort out the flow of AC signals and make the necessary impedance transformation between coaxial cable, which has a low impedance, and balanced loads, which have higher impedances.
Where should choke balun be placed?
Current maxima along the coaxial line are good locations for inserting a sheath current choke. Current minima should be avoided. A current balun at the center of the feeding element should also be used with this type of antenna.
What does a 1 to 1 balun do?
Key uses for the 1:1 current-balun: a) is to marginalize the “inverted-L current” in the transmission-line feeding a dipole-antenna. This will prevent a radiating Feedline and prevent distorting the antenna’s radiation pattern. There will be some flux in the core but it’ll be minor due to the small current causing it.
Where does the common mode choke go?
Common mode current occurs due to coupling between the antenna and the coax shield, so if you place the choke at the feedpoint, you break the circuit and most of the common mode current will be blocked. (The circuit is from the antenna, though the coax, and back to the antenna via RF.)