# Filter-Spice

```ECEN 2420, Electronics for Wireless, Spring 2016
Prof. Zoya Popovic
HOMEWORK 3 – TAKE-HOME PART
Assigned
Due
Covers pages
st
th
February 1
February 8
65-70
No
th
Turn in: Monday, February 8 , in Homework Session 6:15-9:30pm
Homework Policy: You are allowed to work with others on homework, BUT under 2 rules:
o Rule 1: You write your own solutions.
o Rule 2: You list all the other students with whom you collaborated on the assignment at
the top of your homework.
3.1. Simulating filters in LT-Spice
In this part of the homework, you will simulate the harmonic filter of the NorCal40A radio using
LT-Spice. Use a low-pass ladder filter with 3 shunt (parallel) capacitors and 2 series inductors.
The capacitors are C1(=C45)=330pF, C2(=C46)=820pF and C3(=C47)=330pF. The numbers in
parentheses are the numbers indicated on the printed circuit board you will use later. Design the
inductors L1(=L7) = L2(=L8) so that the cutoff frequency is 7MHz. Simulate it from 0-28MHz
(fourth harmonic) using a 50-ohm impedance at the output (scope) and a 50-ohm generator.
Answer the following questions:
Q1: What are the inductor values?
Q2: Plot the input impedance of the filter as a function of frequency and attach to this sheet.
Q3: What is the loss at 7MHz?
Q4: What is the loss at 14MHz?
Q5: How does changing the values of the capacitors change the filter response? Use a few (e.g.
3) existing values of capacitances, such as 100pF, 120pF, 200pF 240pF, 300pF, 390pF, 510pF,
680pF, 750pF and 910pF to test the behavior. Next, vary the first inductor by ±10 and ±50% and
record the behavior.
Q6: Summarize your conclusions and attach summary. No need to do a lot of writing, just
bullets with main conclusions are sufficient. A table which shows the results (cutoff frequency,
and any other parameter you choose) as a function of the values would be a good way to do this.
Q7: How would you make a filter with more rejection?
```