RF Signals

RF (short for Radio Frequency) signals are sinusoidal waves with frequencies in the MHz and GHz range.

While there are RF sources designed specifically for these frequencies, our good friend the Rigol Function Generator can produce frequencies in the lower end of the RF spectrum and should be sufficient for investigating RF signals. These were discussed in detail here. You should review their operation if needed, especially the section on performing Fourier Transforms, as they will be used extensively below.

For this module, you will need

• Rigol DG1022 Function Generator
• Rigol DS1102E Oscilloscope
• Micro-circuits ZAD-1 RF mixer
• A selection of BNC cables
• Thorlabs Variable Resistance Terminator

Measuring RF Power

Connect the output of channel 1 of the function generator through the terminator (set to 50ohm) to channel 1 of the function generator.

1. Set channel 1 of the function generator to create a 1V amplitude sine wave with a frequency of 4MHz.
2. Set the horizontal and vertical scales of the scope to view the wave. Make sure the trigger for the scope is set to be on channel 1.
3. Use the scope's measure function (or the scope's cursor) to get the amplitude of the wave. Is it what you expect? What is the amplitude if you remove the terminator? Does that make sense?
4. Use the math menu to create a fourier transform of the signal. With the cursor, does the frequency the scope reads match what the setting from the scope? If it doesn't, why do you think that might be?

Mixers

Mixers combine RF frequencies, either summing or subtracting them. Each mixer has 3 inputs

1. Local Oscillator(LO)
2. Radio Frequency (RF)
3. Intermediate Frequency (IF)

Mixer:

Subtraction:

Input 1: L

Input 2: R

Output : I=abs(L-R)

Addition:

Input 1: L

Input 2: I

Output: R=L+-I

Switches

Topics

• Measuring RF power
• Termination and impedance matching
• Attenuation and filtering
• Splitters, mixers, and switches