Figure 1-22. Doubly balanced modulator

Analyzing Color Video and Video Test Signals
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Figure 1-22.

Doubly balanced modulator

(4) Looking again at Figure 1-19, one can see that the 3.58 MHz CW subcarrier

is applied to the I and Q modulators through delays. The I signal is delayed 57

degrees from subcarrier and the Q signal is delayed 57 + 90 or 147 degrees away

from subcarrier.

This corresponds to the I and Q vectors shown in figure 1-18.

Also, the subcarrier is applied to a burst keyer where a portion of the subcarrier

is inserted onto blanking for use as a color sync.

e. Color synchronization signal.

Since the subcarrier is suppressed at the

colorplexer, the local 3.58 MHz oscillator at the receiver must be accurately

synchronized in frequency and in phase with the master oscillator at the

transmitter. In order to maintain these two oscillators in phase, a short burst of

the transmitter 3.58 MHz oscillator voltage is transmitted at the beginning of each

horizontal scanning line.

(1) The burst is generated at the color frequency standard generator by a

gating circuit which is turned on by burst keying pulses derived from a device

known as a burst flag generator.

This device is also locked in with the station