40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
 40m Log Not logged in Message ID: 4358     Entry time: Fri Feb 25 14:35:06 2011
 Author: Larisa Thorne Type: Update Category: Electronics Subject: Total harmonic distortion results for +7dBm mixer

This experiment deals with measuring the total harmonic distortion (THD) contribution of mixers in a circuit.

(a circuit diagram is attached) where:

Mixer: ZFM-3-S+ at +7dBm

Attenuator: VAT-7+, at +7dB

Low-pass filter: SLP-1.9+, which is set to DC-1.9MHz

The total harmonic distortion can be calculated by the equation: $\mbox{THD} = \frac{V_2^2 + V_3^2 + V_4^2 + \cdots + V_\infty^2}{V_1^2}$

where Vn represents the voltage of the signal at a certain harmonic n.

In this experiment, only the voltages of the first three harmonics were measured, with the first harmonic at 400Hz, the second at 800Hz, and the third at 1.2kHz. The corresponding voltages were read off the spectrum analyzer after it had time averaged 16 measurements. (picture of the general shape of the spectrum analyzer output is attached)

(results for this mixer's particular configuration are on the pdf attached)

There really isn't that much correlation between the modulations and the resulting THD.

We won't know how good these numbers are until more experiments on other mixers are done, so they can be compared. Since the rest of the mixers are relatively high levels (+17dBm, +23dBm in comparison to this experiment's +7dBm), an RF amplifier will need to be hooked up first to do any further measurements.

 Attachment 1: THDcircuit.jpg  27 kB Attachment 2: Photo_on_2011-01-17_at_12.25.png  442 kB Attachment 3: THDwithoutamp.pdf  28 kB ELOG V3.1.3-