Optional (1:1) External Balun
A balun is an electrical circuit used to help resolve the inherent problem of feeding an an-
tenna with an electrically 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 pattern.
Why is it Optional ?:
In the normal configuration, ground mounted
with 12 or more radials, the ground will bleed/
drain the unwanted RF signal from the coax
shield.
When Should You Use A Balun ?:
•
When elevating the base of a vertical
antenna above the ground
•
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
To install the balun (Figure 25) we suggest that you mount
it as shown in Figure 27. There are two holes in the base of
the balun that will line up with two screws in the end of the
element housing unit next to the SO-239 connector. Re-
move these two screws and reinstall them through the balun
then connect the PL-259 as shown in Figure 27. Your feed
line will then plug into the SO-239 in the center of the
balun.
Balun Mounted on BigIR
Figure 27
Optional External Balun
Figure 25
Antenna
Radio
Ferrite
Toroidal
Core
Coax
Figure 23
2112 116TH AVE NE SUITE 1-5, BELLEVUE WA, 98004 WWW.STEPPIR.COM TEL: (425)-453-1910 FAX: (425)-462-4415
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Summary of Contents for BigIR - MK IV Vertical
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