Free AIM Practice Questions

Question 1

A spectrum analyzer displays two strong carriers and a weaker response at a possible third-order product frequency. Increasing its internal input attenuation by 10 dB leaves the input-referred carrier readings unchanged, but the weaker response falls by approximately 20 dB and remains above the noise floor. The analyzer automatically corrects its display for internal attenuation. Which origin best fits the weaker response?

Accepted Answer

An intermodulation product generated within the spectrum analyzer's front end

Answer

Passive intermodulation generated in the antenna feed assembly

Answer

A transmitter spur entering through the measurement cable

Answer

A weak external carrier being reduced by the input attenuator

Question 2

A service note says, 'RSSI increased, so the link has more margin.' Yet the calibrated total-power RSSI rose during digital-radio error bursts, the bit error ratio worsened, and independently measured wanted-carrier power was unchanged. No front-end compression test has been performed. Which interpretation of the measurements is technically sound?

Accepted Answer

The higher RSSI can reflect added unwanted energy rather than increased link margin.

Answer

The wanted signal has gained usable fade margin because the RSSI is higher.

Answer

The combination of higher RSSI and more errors establishes front-end compression.

Answer

The unchanged wanted-carrier power rules out RF interference as the cause of errors.

Question 3

After a feeder jumper is replaced, a sector's PIM result improves from -144 dBc to -157 dBc against a site limit of -150 dBc. Test power remains +43 dBm per tone at the instrument, and dBc is referenced to one tone. However, measured feed-path insertion loss rises from 1.5 dB to 6.5 dB; return loss still passes. How should the apparent PIM improvement be interpreted?

Accepted Answer

Added path loss may mask PIM by reducing junction drive and returning product power.

Answer

The replacement has eliminated the nonlinear source responsible for the original PIM.

Answer

Passing return loss validates the PIM result despite the added feed-path loss.

Answer

Subtracting the added cable loss from the PIM reading will establish the corrected pass result.

Question 4

An interference hunter follows a stable signal toward a metal-clad warehouse. From one street the strongest bearing points at the west wall; after moving around the corner, it points at a different part of the facade. The signal's frequency and burst pattern remain the same. Before attributing the source to equipment inside the warehouse, the most useful field check is to:

Accepted Answer

Obtain bearings from separated positions with different views of the building.

Answer

Plot the two peak-bearing lines and accept their intersection as the emitter's location.

Answer

Use the strongest peak alone, because a reflection must be weaker than the direct path.

Answer

Suspend the search until the warehouse's RF equipment has been shut down.

Question 5

Both ends of a clear line-of-sight link use linearly polarized antennas. Transmit elements are vertical; receive elements are horizontal. Frequency band, impedance match, feeder loss, and boresight alignment are correct. Which adjustment corrects the underlying coupling mismatch?

Accepted Answer

Rotate the receive antenna to vertical polarization.

Answer

Replace the feeder with cable of the same impedance but lower loss.

Answer

Install a higher-gain receive antenna while retaining horizontal polarization.

Answer

Increase receiver gain without changing the receive antenna's orientation.

Question 6

Time-domain measurements on an isolated coaxial feeder show a strong reflection 250 ns after launch. The cable velocity factor is 0.80; use c = 3.00 x 10^8 m/s. Calibration places the reference plane at the feeder input, excluding the test lead. At which accessible point along the feeder should the technician look for the discontinuity?

Accepted Answer

The joint 30 m along the feeder

Answer

The entry gland 24 m along the feeder

Answer

The bend 37.5 m along the feeder

Answer

The antenna connection 60 m along the feeder

Question 7

A current probe encircling both leads of a DC supply cable detects RF current that tracks a receiver's interference. The supply carries 8 A of operating current. A suitable ferrite core is available for the interference frequency. To impede the detected RF current without applying net DC magnetizing current to the core, how should the leads be routed?

Accepted Answer

Pass both leads through one core from the same side.

Answer

Pass only the supply lead through the core and leave the return outside.

Answer

Pass the supply and return leads through separate identical cores.

Answer

Pass the two leads through one core in opposite physical directions.

Question 8

Max hold has revealed intermittent interference at a fixed frequency, but it does not show how long each burst lasts or the interval between bursts. The bursts occupy a known, narrow band and may last only a few milliseconds. Which acquisition would preserve the timing information needed for the next stage of the investigation?

Accepted Answer

Triggered zero span, with bandwidth and time resolution sufficient to resolve each burst

Answer

Successive swept traces with reduced video bandwidth and averaging to stabilize the peak

Answer

A wider frequency sweep with max hold to accumulate the full range of intermittent peaks

Answer

A spectrum with narrow resolution bandwidth, using peak frequency width as burst duration

Question 9

A strong, unmodulated off-channel carrier raises a receiver's in-channel noise floor during a shielded bench test. The RF stages remain below compression. Replacing the local oscillator with a lower-phase-noise source at the same frequency and drive level removes most of the added noise, without changing either RF input signal. What mechanism does this isolate?

Accepted Answer

Reciprocal mixing with local-oscillator phase noise

Answer

Third-order intermodulation in the RF preamplifier

Answer

An image response caused by inadequate RF preselection

Answer

Cross-modulation transferred from the blocking carrier

Question 10

In a shielded two-tone test, a spurious response falls inside a receiver channel spanning 1884.950-1885.050 MHz. The applied carriers are 1935.000 and 1985.000 MHz. Keeping both powers fixed, the technician moves only the higher carrier to 1985.100 MHz. Which new response would support a lower near-carrier third-order intermodulation product?

Accepted Answer

1884.900 MHz, moving below the receiver channel

Answer

1885.100 MHz, moving above the receiver channel

Answer

1885.200 MHz, moving above the receiver channel

Answer

1885.000 MHz, remaining inside the receiver channel

Free AIM Practice Questions

Domain 1: Safety

Question 1

Question 2

Domain 2: Radio Interference Principals - Radio Overview

Question 3

Domain 3: Interference Types - Overview and Corrective Actions

Question 4

Domain 4: Intermodulation

Question 5

Domain 5: Filters - Filter Systems Usage to Mitigate RFI

Question 6

Domain 6: Test Equipment for Interference Hunting

Question 7

Question 8

Domain 7: Finding Interference

Question 9

More AIM practice questions

Question 10

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