14 Understanding Your Tuner
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Understanding Your PALSTAR BT15000A Tuner and Your Antenna
The PALSTAR BT1500A antenna tuner is a highly flexible matching device
intended for use with antennas that use balanced or parallel transmission lines.
To obtain the best performance from the tuner, you should understand how the
tuner works and how it relates to your antenna and feedline.
Basic Operation:
Examine the schematic diagram of your tuner to see all of the
electronic features. In this discussion, we shall focus only upon the matching
network itself. The basic circuit under discussion is a balanced L-network with
the shunt capacitor on the output side.
A single-ended L-network — the most common variety — uses a certain value of
inductance (L) and a certain value of capacitance (C) to effect a match at a par-
ticular frequency for a particular antenna feedline impedance and length. For
coaxial cable systems, the single-ended L-network provides the lowest loss of
any network matching system. However, one limitation is that with the capacitor
on the antenna side of the coil, the system is limited to antenna terminal imped-
ances greater than about 50 Ohms. If we wish to use the single-ended network
with a balanced feedline, we have to add a balun on the output side of the net-
work. Baluns work best with very low values of reactance on their output termi-
nals, a condition that is difficult to obtain with most antennas that use parallel
feedlines.
The balanced version of the L-network overcomes this limitation by providing a
true balanced output directly from the network. For a particular antenna, operat-
ing frequency, and transmission line impedance and length, the matching circuit
requires the same total circuit inductance and the same output capacitance as the
single-ended network. However, the balanced circuit divides the inductance into
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AT1500CV
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Rear Panel Description 7
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12VDC INPUT
(2.1 mm plug) for
12VDC.
RF INPUT Coaxial con-
nector for input from
transmitter or amplifier.
GROUND Post/wing nut
ground connector.
BALANCED OUTPUT
Two Nylon high voltage connectors for
output to RF balanced transmission lines.
Balanced line of any impedance (300Ω,
450Ω, 600Ω) can be used to feed the
antenna.
FIGURE 1 REAR PANEL CONNECTORS
