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A balun is an electrical circuit used to help resolve the inherent problem of feeding an antenna with an electri-
cally unbalanced (coax) feed line. It is intended to present an infinite impedance to any RF current that might
otherwise flow on the outer conductor (shield) of the coax producing radiation from the line. This current, if
high enough, can cause heat buildup and potential damage to the radio as well as a distorted radiation pat-
tern and RF noise.
Why is it Optional ?:
In the normal configuration, ground mounted with 12 or more radials, the ground will bleed/ drain the unwant-
ed RF signal from the coax shield.
When Should You Use A Balun ?:
• When mounting the vertical antenna in an elevated fashion
• When only a few radials are used
• When the coax run is shorter than the radials
• When the ground condition is poor
• Unusual SWR readings on one band
Balun Installation
There are numerous options for mounting the balun—by far the most popular is to mount the balun on an ad-
jacent post or similar structure via the 2 mounting holes molded in its housing. There are 2 locations SteppIR
recommends installing the 1:1 balun. If you have one balun then install it just outside of the radial field. If you
have 2 baluns available to you then do both locations shown in figure 8.1.
Antenna
Radio
Ferrite
Toroidal
Coax
Figure 8.0
OPTIONAL 1:1 BALUN
Figure 8.1
* Top
1:1 balun
SO-239
Coax
Shack
Antenna
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