What condition may be indicated if a VHF radio cannot contact nearby stations on any channel, an inline wattmeter indicates 25 watts output (HIGH power mode), and no modulation is heard when the transmitted signal is monitored with an external receiver?
A fault in the transmitter's Push-To-Talk circuit is causing the loss of audio.
Correct Answer
There is an openconnection in the microphone cable or connector.
The microphone's Automatic Gain Control (AGC) has malfunctioned.
Degenerative feedback applied to the AF amplifier exceeds specifications.
What condition may be indicated if a VHF radio cannot contact nearby stations, an inline wattmeter indicates less than 1 watt output (HIGH power mode), and nominal voltage (e.g., 12.8 vdc) is applied to the VHF radio power input line?
The RF power applied to the input of the Power Amplifier (PA) stage is excessive.
There is an open connection between the radio's PA stage and the antenna connector.
Correct Answer
The bias voltage applied to the Power Amplifier (PA) stage may be insufficient.
A defective capacitor is blocking DC voltage from appearing at the antenna connector.
A spectrum analyzer (SPECAN) can be a useful test instrument to troubleshoot a marine VHF radio. Which of the following is the best procedure to evaluate the input/output stages of a marine VHF transmitter?
Connect the radio to the SPECAN through an in-line attenuator, apply maximum attentuation and set the radio to HIGH power. Use an inductive probe to evaluate signals at the input/output of AF transmitter stages.
Connect the radio to the SPECAN through an in-line attenuator, apply maximum attentuation and switch the radio to HIGH power. Use an inductive probe to evaluate signals at the input/output of RF transmitter stages.
Connect the radio to the SPECAN through an in-line attenuator, apply minimum attentuation and switch the radio to LOW power. Use an inductive probe to evaluate signals at the input/output of AF transmitter stages.
Correct Answer
Connect the radio to the SPECAN through an in-line attenuator, apply maximum attentuation and switch the radio to LOW power. Use an inductive probe to evaluate signals at the input/output of RF transmitter stages.