Figure 3-9. Antenna Tuner Block Diagram

TM 11-5820-919-12

tuner automatically transforms the antenna impedance

3-36. HARMONIC FILTER (Figure 3-8). The harmonic

(reactive/resistive) to 50 ohms. This is done by using an

filter suppresses transmitter harmonics and noise levels

adjustable L-C network. The antenna tuner is normally

outside of the selected frequency band. To do this. the

off, and the L-C network is held in place by magnetic

Xmt/Rcv must pass through the bandpass and pass

latching relays. The antenna tuner becomes operational

filter. The Filter select signal, from the control pilot

whenever. (1) the radio is turned on, (2) the MODE

panel energizes one of the six filter select relays which

switch is changed from V-RCV to V-TR or D-RCV to D-

switches itches the associated filter into the circuit. The

TR, or (3) the frequency is changed. This causes a tune

filters are passive and are used in both transmitter and

start signal to he applied to the L-C control from the

receiver modes. The rf detector circuits monitor the

control panel.

amount of power point to and returning from the antenna

(vswr). The signal is applied to the power amplifier.

3-37. ANTENNA TUNER (Figure 3-9). The antenna

Figure 3-8. Harmonic Fiolter Block Diagram

Figure 3-9. Antenna Tuner Block Diagram

tune and perform a retune if necessary.

3-38. When a tune start is generated, the L-C control

resets the L-C network to zero. This means that there

will be no inductors or capacitors in the Xmt/Rev RF

pathway. When the operator transmits the rf sensor

3-39. If the tuning cycle takes too long (over 12

bridge samples the Xmt RF and produces a Wswr

seconds) the L-C control will output a Tune Fault signal.

signal. In addition, a Tune In Progress signal is sent to

This means that either the selected antenna is not within

the modulator/demodulator. The L-C control uses the

the tuning range of the antenna tuner, or that the

Vswr and the Frequency Select signals to adjust the L-C

module could be faulty . A Tune Fault signal is sent

network to its correct value via the L-C select signals. If

immediately y should a frequency below 2MHz be

a Tune Check Enable is routed from the power amplifier

during transmission, the antenna tuner will recheck its

3-11/(3-12 blank)