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NETW 360 Week 2 iLab: RF Behavior Calculations

Task 1: Power calculations

Use the calculator in the Power section to complete the following steps:

On the lower UNII-1 band (i.e., 5.150–5.250 GHz with 100 MHz channels), the maximum output power of the intentional radiator (IR) allowed by the FCC is 50 mW. The IR is also referred to as a wireless transmitter.

Click in the watts box and type 0.05 (50 mW = 0.05 watts). What is the dBm of 50 mW?

On the middle UNII-1 band (i.e., 5.250–5.350 GHz with 100 MHz channels), the maximum output power of the intentional radiator (IR) allowed by the FCC is 250 mW.

Click in the watts box and type 0.25 (250 mW = 0.25 watts). What is the dBm of 250 mW?

On the upper UNII-1 band (i.e., 5.725–5.825 GHz with 100 MHz channels), the maximum output power of the intentional radiator (IR) allowed by the FCC is 800 mW.

Click in the watts box and type the given power level in watts. What is the dBm of 800 mW?

Scroll down to the Receive Sensitivity section. Review the information regarding receive sensitivity.

The receive sensitivity of a LinksysWUSB600N wireless network adaptor at 54 Mbps is -70 dBm. Click in the dBm box and type -70. What are the watts of -70 dBm?

The receive sensitivity of a LinksysWUSB300N wireless network adaptor at 54 Mbps is -68 dBm. Click in the dBm box and type -68. What are the watts of -68 dBm?

If you have to choose between these adaptors based on their receive sensitivity at the bit rate of 54 Mbps, which adaptor will potentially perform better in achieving the desired bit rate?

Task 2: Cable loss calculations

Use the calculator in the Loss in a Coaxial Cable at 2.45 GHz section to complete the following steps:

Next to Choose type of cable, select LMR 400. This is a TMS cable that supports both 2.4 GHz and 5 GHz RF signals. 100 feet of such cable used on the 2.5 GHz range decreases the signal strength by about 6.76 dB (that is, 6.76 dB signal loss per 100 feet).

Click in the Length (meter) box and type 30.48 (100 feet = 30.48 meters). Click m→dB. What is the loss at this length? __________

Click in the Length (meter) box and type 60.92 (200 feet = 30.48 meters). Click m→dB. What is the loss at this length? __________

When the cable length doubles, how does the loss change, approximately? __________

Task 3: Antenna gain calculations

Use the calculator in the Antenna section to complete the following steps:

Next to frequency band, select 2.41–2.48 GHz.

Next to antenna diameter in meters, type 0.1 (0.1 meters = 3.9 inches). This is an optional antenna that could be added to an access point (AP).

Click D→ dB. What is the maximum theoretical antenna gain? __________

Next to frequency band, select 5.15–5.85 GHz.

Next to antenna diameter in meters, type 0.1 (0.1 meters = 3.9 inches)

Click D→ dB. What is the maximum theoretical antenna gain? __________

Given the same sized reflector, which signals, high-frequency or low-frequency, can be more efficiently focused by parabolic antennas (i.e., result in a higher antenna gain)?

Next to frequency band, select 5.15–5.85 GHz.

Next to antenna diameter in meters, type 0.2 (0.1 meters = 7.8 inches)

Click D→ dB. What is the maximum theoretical antenna gain? __________

Given the same signal frequency, which dish antennas, large-sized or small-sized, are more efficient at focusing the signal (i.e., result in a higher antenna gain)?

Task 4: Free space loss calculations

Use the calculator in the Free space loss section to complete the following steps:

Next to frequency band, select 2.41–2.48 GHz.

Next to kilometers, type 0.1 (100 meters = 0.1 kilometers).

Click dB← km. What is the free space path loss in dB? __________

Change the frequency band to 5.15–5.85 GHz.

Next to kilometers, type 0.1 (100 meters = 0.1 kilometers).

Click dB← km. What is the free space path loss in dB? __________

How does the free space path loss for 802.11a (operating on the 5 GHz band) compare with 802.11g (operating on the 2.4 GHz band)? __________

Next to frequency band, select 2.41–2.48 GHz.

Next to kilometers, type 0.02 (20 meters = 0.02 kilometers).

Click dB← km. What is the free space path loss in dB? __________

Next to kilometers, type 0.04 (40 meters = 0.04 kilometers).

Click dB← km. What is the free space path loss in dB? __________

Next to kilometers, type 0.08 (80 meters = 0.08 kilometers).

Click dB← km. What is the free space path loss in dB? __________

When the distance doubles, how does free space path loss in dB change?

Next to frequency band, select 17.1–17.3 GHz.

Next to kilometers, type 1.

Click dB← km. What is the free space path loss in dB? __________

Next to kilometers, type 2.

Click dB← km. What is the free space path loss in dB? __________

Next to kilometers, type 4.

Click dB← km. What is the free space path loss in dB? __________

When the distance doubles, how does free space path loss in dB change?

Task 5: Link budget calculations

Use the calculator in the Link budget section to complete the following steps:

Enter the following values for an office WLAN:

Transmit—

Transmit output power: +15 dBm

Cable loss: -6 dB

Antenna gain: +2 dBi

NOTE: the previous values are used to compute effective isotropically radiated power (EIRP): (+15 dBm) + (-6 dB) + (+2 dBi) = 11 dBm. By definition, EIRP is the amount of power an ideal isotropic radiator can generate. In reality, EIRP is the power radiated from an antenna; it is regulated by the FCC.

Propagation—

Free space loss: -81 dB

Reception—

Antenna gain: +2 dBi

Cable loss: -4 dB

Receiver sensitivity: -80 dBm

Click Compute. What’s the total remaining margin in dB? __________

Is this margin sufficient to accommodate received signal fluctuations? Why?

Enter the following values for a 10-killometer outdoor transmission link:

Transmit—

Transmit output power: +10 dBm

Cable loss: -3 dB

Antenna gain: +25 dBi

NOTE: the previous values are used to compute effective isotropically radiated power (EIRP): (+10 dBm) + (-3 dB) + (+25 dBi) = 32 dBm. EIRP is regulated by the FCC.

Propagation—

Free space loss: -120 dB

Reception—

Antenna gain: +25 dBi

Cable loss: -3 dB

Receiver sensitivity: -80 dBm

Click Compute. What’s the total remaining margin in dB? __________

Is this margin sufficient to accommodate received signal fluctuations? Why?

Task 6: Link budget calculations

Use the calculator in the Fresnel ellipsoid section to complete the following steps:

Next to distance “D” between transmitter and receiver [meters], type 114. This is close to the maximum distance of an office WLAN.

Next to distance “d” between transmitter and obstacle [meters], type 65. This assumes an obstacle is at the midpoint between two antennas.

Click Compute radius. What’s the radius of the Fresnel zone at the middle point? ________

Next to distance “D” between transmitter and receiver [meters], type 16000. This refers to an approximately 10-mile outdoor point-to-point transmission link.

Next to distance “d” between transmitter and obstacle [meters], type 4800. The obstacle is about 3 miles from one antenna.

Click Compute radius. What’s the radius of the Fresnel zone at this specific location?