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T7A09

PRACTICAL CIRCUITS · Station equipment: receivers, transceivers, transmitter amplifiers, RF preamplifiers, transverters; Basic radio circuit concepts and terminology: sensitivity, selectivity, mixers, oscillators, Push-To-Talk (PTT), VFO, modulation

T7A09T7A →

What is the function of the switch which selects either SSB or CW-FM on some VHF power amplifiers?

  1. AChange the mode of the transmitted signal
  2. BSet the amplifier for proper operation in the selected mode
  3. CChange the frequency range of the amplifier to operate in the proper segment of the band
  4. DReduce the received signal noise
Why On a VHF brick amplifier, that switch is inside the amplifier only, so it cannot change what the radio transmits. It configures the amplifier itself: in SSB position the RF-sensing transmit/receive relay gets a hold-in delay so the amp does not chatter between syllables of speech, and the bias is set for linear amplification. In the CW/FM position the amp is set for constant-carrier, full duty-cycle operation with fast keying.
Watch out The tempting answer is that it changes the transmitted mode, but the mode is generated in the exciter or transceiver; the amplifier just faithfully amplifies whatever it is fed.
The amp doesn't make the mode, it adapts to it: SSB position adds relay hang time, FM/CW position sets full-carrier operation.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
← T7A08 All of T7A T7A10 →

The rest of T7A

  1. T7A01 Which term describes the ability of a receiver to detect the presence of a signal?
  2. T7A02 What is a transceiver?
  3. T7A03 Which of the following is used to convert a signal from one frequency to another?
  4. T7A04 Which term describes the ability of a receiver to discriminate between multiple signals?
  5. T7A05 What is the name of a circuit that generates a signal at a specific frequency?
  6. T7A06 What device converts the RF input and output of a transceiver to another band?
  7. T7A07 What is the function of a transceiver's PTT input?
  8. T7A08 Which of the following describes combining speech with an RF carrier signal?
  9. T7A09 What is the function of the switch which selects either SSB or CW-FM on some VHF power amplifiers?
  10. T7A10 What can be added to the output of a transceiver to increase the transmitted output power?
  11. T7A11 What is the function of the Variable Frequency Oscillator (VFO) circuit in a transceiver?
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