Circuit makes simple FSK modulator

摘要

The need for a compact telemetry system poses a challenge for designing a small, light, low-component-count system. Interfacing serial data from the microprocessor is also difficult because most low-cost RF transmitters do not accept dc levels at the input. Commercial FSK (fre-quency-shift-keying) modulators are bulky and need many passive components. The circuit in Figure 1 uses a single NOT gate (inverter), an On Semiconductor NL27WZ14 in a surface-mount package, to generate continuous FSK data from TTL-level signals.