Skills Mapping
Dr S.Pennock and Dr R. Watson - 20/01/2025
Schedule:
Thursday, Week 10 .

Characterisation of a Down-converter and Transmission Link - to be completed

Introduction

The aim of this experiment is to help students gain familiarity with an upconverter. In the following experiment the downconverter is examined and a complete link formed by connecting the upconverter to the downconverter. This experiment focuses on the characterisation of the upconverter and the features the circuit produces. The experiment, which should be recorded in real time, assumes a basic theoretical knowledge to the level taught in the EE22004 and EE2206 courses. The lecture notes for these courses are available on Moodle.

List of Tests and assessment

Tests

Hybrid

  1. Load LTSpice file ???
    • Initiate LTSpice - don’t share anything
    • File open EE22006_3dB_coupler_transient.asc
    • Explain what is on the screen for simulation set up and measures to be created.
  2. Run simulation
    • Hover over points S, a and b on schematic until ‘scope probe icon’ appears. Click and the waveform should appear in the “filenale.raw” window.
    • Press Ctrl-L and the log file opens. Contains the harmonic components of the signals in amplitude and phase and at bottom of the file the RMS values of the signals at S, a and b. Calculate dB between S and a, S and b. Note relative amplitudes and phases.
  3. Modify L1 - right click on inductor L1, change value to 1.5uH and re-simulate. a and b traces now differ in amplitude and phase. Confirm with data using Ctrl-L.
  4. Now close file and open EE22006_3dB_coupler_ac.asc
    • does ac analysis rather than transient.
    • Run and add probes at S, a and b. Then change L1 to 1.5uH (click on inductor, change value), press Run again - traces from a and b now visibly different.
  5. Open EE22006_3dB_hybridcoupler_transient.asc.
    • Probes at S, a, b and Iso.
    • Run and note this circuit uses preferred values, so things are not now perfect. Use Ctrl-L and note teh phase difference between Phase (not relative phase) of a and b. Calculate dBs between S and A, and S and b, and S and Iso from RMS data at end of file.
    • Change L1 to 1.5uH and re-run. Note change in relative amplitudes (dBs) and phases of a, b, and Iso.
    • Right click on .tran. Change to AC Analysis, Type of Sweep is Linear, No of points is 1000, Start to 2e6, Stop to 18e6 Note amplitude balance and phase balance at 6 MHz, 10 MHz and 14 MHz.

Mixer

  1. Open EE22006_bare_mixer_transient.asc (Centre tapped balanced mixer)
    • Run and probe rf lo and if. Traces are very compressed. To zoom in on part by left click on data grapgh and drag to include are wanted. Zoom into about 8usec to 9usec. Smooth LO trace is at 14MHz. RF is smallest and discontinuous where diodes switch on and off. IF is approximately a sinusoid at 10MHz but with intermodulation products at other frequencies. Crtl-L and measure RMS of RF, LO and IF and find conversion loss IF to RF.
    • To investigate frequency content: – right click, Zoom to Fit, Right click, View, FFT, OK, in Select Visible Waveforms select all 3 waveforms - Gives whole frequency spectrum. Right CLick on Frequency axis legend. Untick Logarithmic, Left to 2M, tick to 2M Right to 70M. Note LO is 14M, IF is 4M and RF produced is 10M and 18M. Observe other intermods are present. Measure amplitudes of LO, IF and RF(LSB), RF(USB). Right click on IF and LO traces to delete so just RF remains. Observe outputs at n RF +- m IF. Screen capture. Measure dBc.

(Modify LO level and run/measure?)

Close close close

Band pass Filter

  1. Load LTSpice file ???
  2. Run simulation
  3. Set monitor points and read
  4. Modify simulation for wider bandwidth and re-run

Up-converter

  1. Load EE22006_vectormod.asc
  2. Run simulation
    • To investigate frequency content: – right click, Zoom to Fit, Right click, View, FFT, OK, in Select Visible Waveforms select all 3 waveforms - Gives whole frequency spectrum. Right CLick on Frequency axis legend. Untick Logarithmic, Left to 2M, tick to 2M Right to 70M. Note LO is 14M, IF is 4M and RF produced is 10M and 18M. Observe other intermods are present. Measure amplitudes of LO, IF and RF(LSB), RF(USB). Right click on IF and LO traces to delete so just RF remains. Observe outputs at n RF +- m IF. Screen capture. Measure dBc.

Citations