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ECET 304 Spring 2010 FM Radio

10. Lab 10 - Final Construction

posted Jun 23, 2010, 3:02 PM by Bill Bai

9. Lab 9 - Impedance Matching and RF Amplifiers

posted Jun 23, 2010, 3:01 PM by Bill Bai

8. Lab 8 - Mixer, IF Amplifier, and Demodulator Fabrication

posted Jun 23, 2010, 3:00 PM by Bill Bai

6. Lab 6 - Frequency Modulation

posted Jun 23, 2010, 2:59 PM by Bill Bai   [ updated Nov 2, 2010, 2:55 PM ]

We skipped this lab due to time constraints on the schedule.  But basically it was investigating how we can send information via frequency modulated signals.

5. Lab 5 - Amplitude Modulation

posted Jun 23, 2010, 2:58 PM by Bill Bai

4. Lab 4 - Voltage Controlled Oscillator

posted Mar 2, 2010, 7:11 PM by Bill Bai

The voltage controlled oscillator is another important piece of the FM radio tuner.  The VCO is the Local Oscillator.  Basically, the VCO selects what frequency the radio is tuned in to.

The nuts and bolts are fairly complex, but what it boils down to is: the output frequency changes as you change the input voltage.  Hence the very descriptive name Voltage Controlled Oscillator.

So the VCO output is connected to one of the mixer inputs.  This creates the harmonics and cross products of the Radio Frequency signal and Local Oscillator Signal at the Mixer output.  As you may recall in the last post, Mixer's create a lot of harmonics and cross products.  The nice thing about them is that each cross product contains all of the information originally embedded in the carrier signal.  The next stage of the radio will be using one of these lower frequency cross products to extract the information.

Lab Report attached,  Haven't gotten it back yet, don't know what I got on it.

3. Lab 3 - Mixers

posted Feb 17, 2010, 5:58 AM by Bill Bai

(Fundamentals, harmonics, and cross products of 100.5MHz and 110.7MHz in a non-linear mixer)
So lab 3 involved mixers.  There are two kinds of mixers: linear and non-linear.  You put two or more signals into a linear mixer and you get an output that consists of the two fundamental frequencies of the inputs (i.e. an op-amp summer).  A non-linear mixer does some interesting things.  Rather than just adding up two signals, a non-linear mixer produces all the harmonics of each input signal.  Furthermore, the cross products of the input signals are also generated (spectrum analyzer screen capture above shows fundamentals, harmonics, and cross products of 100.5MHz and 110.7MHz).  It is a bit complicated to explain, but the important thing about non-linear mixers is that the cross products of the signals include the original information embedded in the carrier frequency.

Here's the rundown: humans can hear 20Hz to 20kHz, i.e. music.  This 20Hz to 20kHz signal is impressed onto an FM radio frequency, 88MHz to 108MHz; this process is called modulation.  When the signal is picked up by our FM radio receiver and gets to the mixer, our local oscillator is set to a frequency 10.7MHz higher than the frequency we want to tune to, this is called high side injection.  The intermediate frequency (IF) of FM radio is 10.7MHz by definition.  Because we set out local oscillator (LO) frequency 10.7MHz above our desired radio frequency (RF),  there will always be a cross product signal present at 10.7MHz on the mixer's output.  

As I said before, every cross product output from the mixer contains all of the information originally encoded on the RF carrier signal.  This 10.7MHz frequency down-conversion allows us to extract this information from the carrier signal.  Remember, the final goal is to extract the 20Hz to 20kHz music/sound information, the mixer gets us halfway from the 88MHz-108MHz FM band down to 10.7MHz, and the demodulator (later on, see diagram below) will extract the 20Hz-20kHz music/sound information.

(From Wikipedia)

Anywho, anyone who actually checks this website will probably go TL;DR on this post, but mixers are just a bit too complex and technical to explain easily.  My lab report attached to this post.  100% because I'm just full of win. =D

2b. Working Bandpass Filter

posted Feb 16, 2010, 9:25 PM by Bill Bai

I took my newly fixed bandpass filter circuit to lab last week and tested it.  Looks like a bad inductor was the culprit the last time.  It works perfectly.  I totally forgot to take a screen capture of the spectrum analyzer though.  I'll be sure to take one next lab and post the screen cap up here.


posted Feb 8, 2010, 10:16 PM by Bill Bai

Pictures from the entire project so far.

FM Radio Receiver

2a. New Inductors

posted Feb 3, 2010, 7:52 PM by Bill Bai   [ updated Feb 8, 2010, 10:14 PM ]

Ordered some new inductors for my bandpass filter from Lab 2 from Digikey.

IndexQuantityPart NumberManufacturer Part NumberDescriptionCustomer ReferenceBackorder QuantityUnit Price
Extended Price
12495-1968-1-NDB82422A3271K100INDUCTOR .27UH 235MA 1210 10%270NH00.55000$1.10
22495-1713-1-NDB82422A3220K100INDUCTOR .022UH 600MA 1210 10%22NH00.55000$1.10
Estimated Sales Tax$0.15

Total cost is $4.39 in U.S. currency, including $1.90 postage.

I got my new inductors about a day or two after I ordered them, which is crazy awesome fast.  But the packaging is pretty ridiculous.  Here's some pictures of the unboxing and soldering them on to the PCB.

Bandpass Filter Inductor Replacement

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