Chapter 5
TM 11-5985-355-13
transmitter.
5-2. Matching Unit-Base MX-9146/GRC
5-1. General
The MX-9146/GRC consists of a group of shunt
Antenna AS-2731/GRC consists of Matching Unit-Base
reactance components, a rotary latching solenoid (part of
NIX-9146/GRC and an Antenna Element AS-2732/GRC.
S1), and a rotary switch (S1). Rotary switch S1, which
The MX-9146/GRC matches (max VSWR 3.5:1) the
may be positioned manually or automatically, selects the
impedance of the 5-1/2-foot, vertical whip antenna to the
shunt reactance that is connected to the base of the whip
50-ohm transmitter output impedance and receiver input
antenna portion of the AS-2732/GRC. The rf output from
impedance over the entire frequency range of 30 to 80
the receiver-transmitter is fed through connector J1 (fig.
NMHz.
FO-1), a matching network, helical choke L16, and
a. Antenna Element AS-2732/GRC is a single
connector J3 directly to the whip antenna.
a. Components. The components which form the
whip antenna consisting of straight copper conductor
shunt reactances, and the segment of the frequency
placed between two layers of bonded glass fiber strip,
band in which they are used, are listed in the chart
and either a brass or aluminum coaxial cable enclosed
below.
by a fiberglass envelope mast. The AS-2732/GRC is fed
b. Control Voltages. When a compatible
with rf energy at the junction of the straight conductor
and the coaxial cable through a coaxial transmission line
receiver-transmitter is connected through connector J2
in the lower quarter of the antenna. The transmission
of the IMX-9146/GRC, the rt unit supplies control
line also uses shunt reactors to provide a good standing
voltages (nominal +25 volts dc) to the MX-9146/GRC. In
wave ration (swr) at the base of the whip section. The
Receiver-Transmitter, Radio RT-246/VRC or RT-524
VRC (TM 11-5820401-34-2), these control voltages are
element, is an extension of the center conductor of the
supplied by the band switch and a cam-operated switch
coaxial transmission line.
driven by a gear train. In the RT-246/VRC, the cam-
b. The AS-2732/GRC impedance is matched to
operated switch is S309; in the RT-524fVRC, it is S359.
the receiver-transmitter by the MX-9146/GRC. Current
Both switches function identically.
Functioning of Input Control Voltage.
distribution in the AS-2732/GRC is controlled at a
c.
particular frequency by a helical inner conductor sleeve
Depending on the position of the cam-operated switch in
choke and a selected shunt reactance in the IX-
the receiver-transmitter, +25 volts dc is fed through
9146/GRC. These shunt reactances are manually or
terminal D, E, F, G, or H of MX-
automatically selected by a compatible receiver-
Band
Frequency range of
Capacitor
Inductor
segment (MIHz)
A
30-33
C12-C16, C20
L7, L11, L12
A
33-37
C10, C11, C17, C21, C26
L 9, L10
A
37-42
C9, C19, C22, C23
L5, L6
A
42-47.5
C18, C24
L8
A
47.5-53
C8
L4
B
53-56
C7
L3
B
56-60
C7
L3
B
60-65
C6
L2, L15
B
65-70.5
C2, C3
L14
B
70.5-80
C4, C5
L13
5-1
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