Ham Radio Technician Test Equipment & Tools Usage 5 — Questions and Answers
Question 1: What test equipment would you use to verify that a newly built low-pass filter is suppressing harmonics above 30 MHz?
- Multimeter set to AC voltage
- Spectrum analyzer with a tracking generator or a network analyzer (Correct answer)
- SWR meter only
- Frequency counter
Correct answer: Spectrum analyzer with a tracking generator or a network analyzer
A spectrum analyzer (with tracking generator) or network analyzer can sweep the filter's frequency response to confirm attenuation at harmonic frequencies.
Question 2: Why is it important to ground the outer shield of a coaxial cable at the point where it enters a building?
- To increase cable bandwidth
- To protect against lightning-induced surges and reduce RF interference entering the shack (Correct answer)
- To raise the impedance to 75 ohms
- To prevent the cable from picking up audio frequencies
Correct answer: To protect against lightning-induced surges and reduce RF interference entering the shack
Bonding the coax shield to a grounding electrode at the building entry point diverts lightning energy to ground before it can travel to equipment inside.
Question 3: What is the function of a bias-T in an antenna system?
- It matches a 75-ohm feedline to a 50-ohm radio
- It allows DC power to be fed through a coaxial cable to power remote devices such as preamps (Correct answer)
- It converts single-ended coax to a balanced line
- It prevents standing waves on the feedline
Correct answer: It allows DC power to be fed through a coaxial cable to power remote devices such as preamps
A bias-T injects DC voltage onto the center conductor of coax so a remote preamplifier or active antenna can be powered through the feedline.
Question 4: An operator notices their received audio has a 60 Hz hum. Which of the following is the most likely cause?
- The transmitter is running at excessive power
- A ground loop or inadequate filtering in the power supply is coupling AC hum into the audio chain (Correct answer)
- The antenna SWR is above 3:1
- The squelch is set too low
Correct answer: A ground loop or inadequate filtering in the power supply is coupling AC hum into the audio chain
Sixty-Hz hum almost always traces to power-supply ripple or a ground loop where different equipment grounds differ in potential, modulating audio with AC frequency.
Question 5: What is the purpose of ferrite beads or a common-mode choke on a feedline near the transmitter?
- To tune the antenna to resonance
- To suppress common-mode RF current flowing on the outside of the coax shield (Correct answer)
- To reduce the DC resistance of the feedline
- To increase the SWR bandwidth
Correct answer: To suppress common-mode RF current flowing on the outside of the coax shield
Common-mode chokes (ferrite beads or wound coax) present high impedance to RF currents traveling on the coax shield's exterior, preventing them from entering the shack.
Question 6: When installing a mobile VHF/UHF antenna on a vehicle, what is the purpose of making a good DC ground connection to the vehicle chassis?
- To supply operating voltage to the radio
- To provide an RF ground plane that improves antenna performance and reduces noise (Correct answer)
- To prevent the antenna from vibrating at highway speeds
- To meet FCC Part 95 requirements
Correct answer: To provide an RF ground plane that improves antenna performance and reduces noise
The vehicle chassis acts as the antenna's ground plane; a solid RF bond between the antenna mount and chassis ensures efficient radiation and minimizes noise pickup.
Question 7: What tool is used to properly install BNC and N-type crimp connectors onto coaxial cable?
- Needle-nose pliers
- A calibrated torque wrench
- A coaxial crimp tool matched to the connector size (Correct answer)
- A soldering iron alone
Correct answer: A coaxial crimp tool matched to the connector size
Crimp connectors require a crimp tool with the correct die size to deform the ferrule uniformly around the braid, creating a reliable mechanical and electrical connection.
Ham Radio Technician Test Equipment & Tools Usage 5
What test equipment would you use to verify that a newly built low-pass filter is suppressing harmonics above 30 MHz?