Chapter 5

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

upper three quarters of the antenna, the radiating

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

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)

30-33

C12-C16, C20

L7, L11, L12

33-37

C10, C11, C17, C21, C26

L 9, L10

37-42

C9, C19, C22, C23

L5, L6

42-47.5

C18, C24

47.5-53

53-56

56-60

60-65

L2, L15

65-70.5

C2, C3

L14

70.5-80

C4, C5

L13

5-1