Free LAS Practice Questions

Question 1

During troubleshooting, an antenna system shows poorer coverage but a higher input return loss than at commissioning. A calibrated two-port test confirms increased insertion loss in the still well-matched feeder. Direct measurement at the antenna shows unchanged match; calibration and the test reference planes have been verified. What best explains the input result?

Accepted Answer

Greater feeder attenuation is weakening the returning antenna reflection.

Answer

The antenna's resonant frequency moved closer to the operating band.

Answer

A new feeder discontinuity produces a stronger reflection near the transmitter.

Answer

A calibration change left additional test-lead attenuation inside the measured path.

Question 2

An array must aim its elevation main beam farther downward while its housing and polarization orientation remain unchanged. Its adjustable feed network supports the required tilt. Which control should be used?

Accepted Answer

Adjust relative element-feed phases with the electrical-tilt control.

Answer

Introduce additional feedline loss while retaining the existing antenna orientation.

Answer

Change the antenna azimuth so the coverage edge intersects the intended service area.

Answer

Add mechanical downtilt to lower the main beam while keeping the same feed settings.

Question 3

At a shared radio site, the crew disconnects its transmitter and isolates the feeder's DC supply before a sweep. Other tenants remain on air. The analyzer has separate spectrum and cable-test ports, and only the spectrum-port input rating has been checked. Which step is necessary before connecting the feeder to the cable-test port?

Accepted Answer

Check coupled RF at the feeder and the cable-test port's own input limits.

Answer

Approve the connection because disconnecting the local transmitter removes RF from the feeder.

Answer

Use the spectrum-port rating because both ports share the same analyzer enclosure.

Answer

Disable the analyzer's sweep output so incoming RF cannot damage the test port.

Question 4

To make a quarter-wave stub for a 150 MHz matching network, a technician cuts 0.50 m of coax using free-space wavelength. The cable's velocity factor is 0.66. Neglect connector and end effects, and use c = 3.00 × 10^8 m/s. What correction is needed before final tuning?

Accepted Answer

Shorten the coax to approximately 0.33 m.

Answer

Keep the coax at its present 0.50 m.

Answer

Lengthen the coax to approximately 0.66 m.

Answer

Lengthen the coax to approximately 0.76 m.

Question 5

Both the in-band return-loss sweep and the insertion-loss test of an antenna feed path satisfy their limits. With the test setup verified, the required passive-intermodulation test fails. Loose conductive particles are then found inside a connector. What interpretation reconciles these results?

Accepted Answer

An impedance-matched connector can still contain a nonlinear junction that generates mixing products.

Answer

The acceptable return loss rules out the inspected connector as a source of the PIM.

Answer

Two strong carriers generate mixing products in a linear connector even when its contacts are clean.

Answer

The failed PIM test indicates an impedance fault whose location should also appear on DTF.

Question 6

A sweep is calibrated at the test-lead tip. A 50 Ω adapter is then added for the antenna. How can the adapter's full response be excluded from the antenna measurement?

Accepted Answer

Repeat calibration at the adapter's antenna-facing connection.

Answer

Keep the existing calibration because both interfaces are rated 50 Ω.

Answer

Subtract the adapter's insertion loss from the measured return loss.

Answer

Apply only an electrical-delay correction equal to the adapter's delay.

Question 7

One feeder has an 80 mm radius bend that remains fixed at the shelter entrance and an 80 mm radius service loop that flexes whenever an equipment drawer opens. The cable specifies a 25.4 mm minimum installation bend radius and a 101.6 mm minimum repeated-bend radius. Both sections pass their RF tests. Which routing needs revision?

Accepted Answer

Only the moving service loop needs a larger radius.

Answer

Only the fixed entrance bend needs a larger radius.

Answer

Both bends must meet the larger repeated-bend radius.

Answer

Neither bend needs revision if the RF tests pass.

Question 8

A bench test compares an antenna with a 50 Ω dummy load. Both show 20 dB return loss at the same frequency, each measured directly at its input with a 50 Ω reference. What do the matching readings establish?

Accepted Answer

Their reflected-power fractions are equal at that frequency.

Answer

Their radiation efficiencies are equal at that frequency.

Answer

Their power-handling ratings are equal at that frequency.

Answer

Their dissipated-power fractions are equal at that frequency.

Question 9

A calibrated analyzer shows −3 dBm for each of two resolved, independent carriers. Both pass through one matched external attenuator whose loss is 30 dB at each carrier frequency; no external-loss correction is enabled. What combined power, to the nearest whole dBm, should the technician record at the attenuator's input?

Accepted Answer

+30 dBm

Answer

+27 dBm

Answer

+33 dBm

Answer

+54 dBm

Question 10

After a vertical omnidirectional antenna is replaced, distant mobiles receive a stronger signal but users close to the tower base receive a weaker one. Transmitter power, feeder loss, and polarization are unchanged. The replacement has greater horizon gain, a narrower elevation pattern, and 360° azimuth coverage. Why can both coverage results occur?

Accepted Answer

The narrower elevation lobe directs less energy toward nearby users well below it.

Answer

Greater gain improves every elevation, so the nearby weakness indicates new feeder damage.

Answer

The replacement changed polarization, increasing mismatch with the nearby mobiles.

Answer

A vertical omni radiates most strongly along its axis, beyond the nearby service area.

Free LAS Practice Questions

Domain 1: INTRODUCTION TO ANTENNA SYSTEM COMMISSIONING. Commissioning purpose, benefits and available methods; TDR/FDR comparison and the role and limits of a stand-alone VNA; safe equipment use; system diagrams, common components and commissioning records.

Question 1

Question 2

Domain 3: RADIO FREQUENCY (RF) MATHEMATICS. Absolute values; decibel power ratios; dBm, dBc, dBd and dBi references, including the 2.15 dB dipole/isotropic difference; power and voltage ratios and their conversion to dB; adding/subtracting dB and instrument-assisted calculations.

Question 3

Question 4

Question 5

Domain 6: RF CONNECTORS AND CONNECTORIZATION. Appropriate RF connector types and their specifications; installation tools, cable preparation and torque requirements and errors; passive intermodulation and its effects.

Question 6

Question 7

Question 8

Question 9

Question 10

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