[TowerTalk] Balun dimensions

[Jim Brown]

The Fair-Rite data sheets showing recommended frequency range are for a 
single turn for the core. The most detailed data sheet for each 
suppression part include curves for 1, 2, and 3 turns, and provide FAR 
less choking impedance than needed to kill receive noise and to prevent 
feedline pickup from filling nulls in the pattern of a Yagi.

My designs are for CHOKES, not "baluns," and are based on suppression of 
receive noise and pattern control, and provide guidance for power 
handling. Depending on the design of the antenna, they MAY work as a 
"balun," but may defeat coupling action with some multiband designs. For 
example, at least one of N6BT's excellent designs is happy with a 2-wire 
line choke, but not a RG400 choke. My recommendation is to use whatever 
matching device is provided by the mfr, and add the choke between that 
and the feedline.

My designs are intended for use at the feedpoint of antennas that are 
reasonably well matched to their feedline. Secondary uses are as "egg 
insulators" on feedlines to antennas like high dipoles, to prevent their 
interaction with nearby verticals.

Chokes at feedpoints also minimize interference between stations with 
closely spaced antennas, like Field Day, DXpeditions, and and 
multi-transmitter contesting stations.

73, Jim K9YC

On 6/25/2025 12:58 PM, Jim Lux wrote:
> I use 31 mix up to 30 MHz (and higher) to good effect.
> 
> The real part of the impedance keeps going up to 1GHz  (that's the lossy component)
> The imaginary part peaks at about 30 MHz, is decent to 100 MHz, and then falls off. (that's the pure inductance)
> 
> https://fair-rite.com/31-material-data-sheet/
> 
> don't forget that Z is mu*frequency, so even though both real and imaginary parts of my start to roll off at 2MHz, the*impedance*, which is what you want for a choke, keeps going up.