Receivers and Transmitters Flashcards
7 cards from real GROL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Receivers and Transmitters flashcards as text
When measuring RF output power of a transmitter with a wattmeter, the instrument should be connected:
Answer: In the transmission line between the transmitter output and the antenna or dummy load
The RF wattmeter must be inserted in the transmission line at the transmitter output so it measures actual RF power flowing toward the antenna.
A dummy load is used during transmitter testing because it:
Answer: Allows full-power testing and alignment without radiating a signal on the air
A dummy load is a non-radiating resistive termination that dissipates transmitter power as heat, permitting on-air testing and adjustments legally and without interference.
A receiver sensitivity specification of 0.5 µV for 12 dB SINAD means:
Answer: A 0.5 µV RF input produces a (signal + noise + distortion) to (noise + distortion) ratio of 12 dB
SINAD (Signal + Noise + Distortion / Noise + Distortion) is the standard FM sensitivity metric; 12 dB SINAD at 0.5 µV defines a commonly used benchmark.
Receiver blocking or desensitization occurs when:
Answer: A strong off-channel signal saturates receiver stages and reduces sensitivity to the desired weak signal
A strong interfering signal — even well off-frequency — can compress or saturate early receiver stages, reducing gain for the desired signal.
The squelch circuit in a communications receiver serves to:
Answer: Mute the audio output when no carrier or signal above a set threshold is present
The squelch monitors noise level or signal strength and opens the audio only when a valid signal exceeds the set threshold, eliminating between-transmission noise.
"Birdies" or phantom signals heard in a superheterodyne receiver are caused by:
Answer: Spurious internal responses from local oscillator harmonics or unwanted mixer products within the receiver
Birdies appear at specific tuned frequencies because harmonics of the local oscillator (or other internal signals) mix to produce outputs within the IF passband.
An antenna tuner (impedance matching network) between a transmitter and antenna is used to:
Answer: Transform the antenna feedpoint impedance to match the transmitter's required load for maximum power transfer
Maximum power transfer from transmitter to antenna occurs when the load impedance seen by the transmitter matches its design output impedance; the tuner performs that transformation.