Homework #3



Homework #3

Due September 25, 2003

Show your work!

1. What is the noise power in watts on a hot day (100 ˚F in the car) of a CDMA receiver-amplifier with a 1.25 MHz bandwidth and a 3 dB noise figure?

2. An AMPS receiver system with a 30 kHz channel bandwidth and a noise figure of 6 dB for the phone is connected through a coaxial cable with 5 dB of loss to an antenna at room temperature (17 ˚C). What is the noise figure of the receiver system referenced to the antenna input?

3. Problem 5.4 in Sklar

4. Problem 5.5 in Sklar

5. A receiver antenna has an output of 10 µV (carrier only) when connected to a 50 Ω receiver.

a) Determine the power level in the receiver input in watts and dBm.

b) The receiver has one Low Noise Amplifier (LNA) with 10 dB of gain and a noise figure of 3 dB, followed by a mixer with 6 dB of loss in converting the signal to an IF, followed by a filter with 1 dB insertion loss, and a string of several IF amplifiers with 20 dB of gain and a noise figure of 10 dB. How many IF amplifiers are required to produce at least 1 mW to the detector?

c) If you need to add a PAD (an attenuator) in the chain to get exactly 1 mW of output power, what size attenuator is needed?

d) What is the final SNR at the output?

e) Sketch a block diagram of this “superheterodyne” AM receiver showing the power level (in dBm) at each block.

6. Go to the class web site and download rfsyscalc2.xls. You can also open the Word document Rfsyscalc2.doc for an explanation of the terms in the EXCEL spreadsheet. Print out the EXCEL spreadsheet page (as is) and attach it to your homework. Alternatively, you can go to . You must register by clicking on “Sign-In” on the right and giving them your name and e-mail address (no fee required). Go to the software download page at . Under the pull down menu on the left, select “General rf/Microwave”, click on “Go”, and download RF System Calculator. You will have to unzip it (I used UnStuffit which is available on the web).

7. Input the parameters in problem 5 (assuming no interference tones…≈-100 dBm) into the rfsyscalc2.xls spreadsheet. If the channel bandwidth is 30 kHz, what is the final SNR of the system? Attach a print out of the result.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download