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Model 10811A/B
43
Figure 8-4. Mode Suppression
8-16. Figure 8-5 show the equivalent crystal circuits with the tuning capacitor C1.
Figure 8-5. Frequency Tuning Circuit
8-17. C1 tuning capacitor is available from the top of the oscillator outer housing. The change in
reactance of C1 allows the oscillator's frequency to be varied over a 20 Hz (2 X 10
-6
) range. C9
and C4 are dc blocking capacitors.
8-18. ELECTRONIC FREQUENCY CONTROL (EFC)
8-19. To allow for a fine tuning control, a varactor (CR1) is added in parallel with C1 tuning capacitor.
See
. The varactor's capacitance depends on the dc voltage applied to it (reverse bias).
The HC voltage range is +5 volts to -5 volts, giving a fine tuning range of
≈
1 Hz (1 X10
-7
). Since
one side of the varactor is tied to a reference (6.4V), a full +5 volts applied to the HC input will still
keep CR1 reverse biased. C2 and C3 are again dc blocking capacitors to keep the HC current
from flowing in to the crystal circuit. Note: if the HC input is not used, it must be connected to
ground to keep any noise from modulating the HC line and causing frequency changes.
Содержание 10811A
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