RF Fundamentals (15%)

350-101 · 45 questions

• At a stadium, a phone still shows a moderate received signal during the event, but throughput collapses as the noise floor rises. Which measurement explains that collapse better than the signal number alone?
• A hospital mounts a corridor access point, then installs a lead-lined imaging door between that access point and the waiting room. Waiting-room clients fall to a much weaker signal, while a laptop that stays beside the access point does not change. Which propagation effect accounts for the waiting-room drop?
• A logistics engineer compares two access-point power settings, 17 dBm and 20 dBm, on the same radio and antenna. Which statement about the 20 dBm setting is correct?
• A stadium designer replaces a low-gain omnidirectional antenna with a higher-gain directional antenna aimed at one seating section, using the same radio transmit power. What changes in the coverage pattern?
• A logistics engineer reads a radio configured at a high transmit power and cannot understand why a handheld at the end of the aisle shows a weak received signal. What is the engineer comparing incorrectly?
• A university raises the lowest mandatory data rate on a residence WLAN. Students near the access points stay connected, and students at the edge of the same rooms can no longer associate. Why did the edge fail?
• A stadium survey with a laptop shows a healthy downlink, but phones in the same seats keep failing while the laptop still works. The phones transmit at lower power than the access point. What is the limit?
• A warehouse with floor-to-ceiling metal racks has clients whose signal flutters sharply even when they stand near an access point with a clear view of it. Which propagation effect are the racks adding?
• A hospital break room has constant client retries on 2.4 GHz. A spectrum capture of that channel shows continuous energy that is not an 802.11 signal, and no extra beacon is present. What is the source?
• A stadium radio is set to 15 dBm conducted power, the antenna is rated 5 dBi, and the cable loss is 2 dB. What is the EIRP?
• Two neighboring hospital access points are both on the same channel. Client SNR looks healthy, and throughput falls whenever both cells are busy. What is hurting throughput?
• A lecture-hall access point is a four-stream radio. A tablet with a single radio chain never reaches the four-stream data rate, even when it sits next to the access point at high SNR. What limits the rate?
• A logistics client stands around a concrete corner with no line of sight to the access point and still hears a weak signal that fades as they move deeper behind the corner. Which propagation effect is filling in that shadow?
• A handheld shows a received signal of -65 dBm and a noise floor of -90 dBm. What is the SNR?
• A logistics bridge aims a directional antenna at a far building. One antenna is mounted vertical and the other horizontal. The link is much weaker than the same antennas aligned the same way. What is wrong?
• A hotel corridor is long and narrow. A ceiling omnidirectional antenna covers a round blob and leaves the far end of the corridor weak. What antenna choice fits the corridor better?
• A stadium access point is mounted high and aimed flat. Seats far across the bowl hear it, and seats directly below are weak. The radio power is already moderate. What should change?
• A campus path that looks short on a map crosses a row of trees and metal sculpture. The signal at the far bench is jumpy and weaker than the same distance across open lawn. Which effect are the trees and sculpture adding?
• Two clinic access points sit next to each other on channels 1 and 2 in the 2.4 GHz band. Clients near both hear errors even when the noise floor is otherwise quiet. What is the overlap?
• An engineer compares a radio at 10 dBm with the same radio at 20 dBm. Which statement is correct?
• Two scanners sit on the same access point with the same noise floor. One shows a received signal of -45 dBm and the other shows -75 dBm. Which statement is correct?
• A bank survey finds an access point that is not in the inventory and is beaconing the corporate SSID. The corporate radios show beacons from it on the same channel. What is it?
• Two hallway antennas are fed with the same conducted power. One is 6 dBi and the other is 9 dBi. How do they compare in the main lobe?
• A stairwell is usable on 2.4 GHz and nearly dead on 5 GHz from the same access point through the same wall. What does that difference illustrate?
• A phone and a laptop sit in the same spot and show the same received signal. The phone has one spatial stream and the laptop has two. The laptop holds a higher rate. Why?
• Two seats show the same received signal from an access point. The noise floor is much higher at the second seat, and the laptop there holds a lower rate. Why is the rate lower?
• A logistics bridge had a stable outdoor link. A new structure now rises into the space around the visual line of sight, and the link fades even though both antennas still point at each other. What did the structure enter?
• A lab inserts a 6 dB attenuator between a radio and its antenna. About how much of the conducted power reaches the antenna?
• Handheld scanners in a warehouse support 2.4 GHz only. The new capacity WLAN is 5 GHz only, and the scanners never see it. What does the design still need for those scanners?
• A survey in an empty hangar measures a signal, then moves the laptop to twice the distance from the same access point with nothing in the way. About how much does free-space loss increase?
• An omnidirectional antenna on a high ceiling is replaced with a higher-gain omnidirectional antenna to reach the floor below. The floor below gets weaker. Why?
• A clinic laptop holds a low rate beside a lab appliance. The appliance is removed, the received signal stays the same, the noise floor drops, and the rate rises. Why did the rate rise?
• A client hears one access point at -55 dBm and another at -75 dBm. The weaker reading comes from the access point with the higher configured transmit power, which is much farther away. Which reading should drive the design?
• Clients in a lobby attach to an access point that beacons the corporate SSID at a stronger signal than the corporate radios. That access point is not in the inventory. Why do the clients attach to it?
• A rooftop run has 10 dB of cable loss between a radio and the antenna. About how much of the conducted power arrives at the antenna?
• Two neighboring clinics put 20 MHz radios on channel 1 and channel 3 and expect no overlap. The radios still interfere. Why?
• An upstairs access point hears the downstairs 2.4 GHz radio strongly, and the two contend. The downstairs radio is on the ceiling of the floor below. What is the propagation fact?
• A survey shows a received signal of -45 dBm and a noise floor of -85 dBm. Which signal-to-noise ratio matches those two readings?
• A warehouse channel shows a steady high noise floor, and a spectrum check shows constant energy from a wireless camera. No beacons come from that camera. What is it?
• Laptops work through a warehouse aisle. A one-stream handset with lower transmit power drops in the same aisle. The design was surveyed with a laptop only. What should the cell be designed for?
• A high-ceiling antenna aimed at the horizon is strong at the far wall and weak in the seats below it. What change aims the energy at the seats?
• A directional antenna points down a hall. A client behind the antenna, in the opposite direction, has a weak signal a few meters away. What is the client sitting in?
• A radio is set to 14 dBm conducted, the antenna is 6 dBi, and the cable loss is 2 dB. What is the EIRP in the main lobe?
• A corporate channel has a high noise floor and no extra beacons. A rogue access point is beaconing the corporate SSID on a different channel. What is the noise on the corporate channel?
• An access point is configured for 20 dBm, and a client at a desk hears it at -70 dBm. An engineer adds those two numbers and treats the sum as the link quality. What is wrong with that?