Figure 4-6. Regenerative Divider, Simplified Schematic Diagram

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

are in the frequency range of one-half the vco frequency

4-81. To maintain regeneration over the range of the

are amplified by Q4 and applied to the local oscillator

three voltage-controlled oscillators, varactor CR2 tunes

port of mixer Z1. Mixer Z1 mixes the vco frequency with

the output tank circuit (T2 and CR2) of Q4 to one-half the

the frequency present at the local oscillator port to

center frequency of the frequency band enabled. For

produce a difference frequency at the if output. For this

high-band vco frequencies (320 to 400 MHz), varactor

circuit to be stable, the frequency present at the if output

tuning voltage (about 13 V dc) developed across R40 of

must be equal to the frequency applied to the local

voltage divider R37-R40 is applied through resistor R30

oscillator port. This occurs only when the if output is

to the cathode of varactor CR2. This decreases the

exactly equal to one-half the vco frequency. (Vco

capacity of CR2 causing the resonant frequency of T2

frequency mixed with one-half vco frequency equals one-

and CR2 to be approximately 180 MHz. For midband

half vco frequency.) As a result, for any vco frequency

vco frequencies (250 to 320 MHz), the logic 1 midband

applied, the circuit locks up and becomes regenerative at

decoder output voltage turns midband switch Q6 on.

one-half the vco frequency.

This connects R38 in parallel with R40 to reduce the

varactor

tuning

voltage

4-19

TO 31R2-2GRC171-2