Fixing the MHS-5200A

Today we make some simple and cheap modifications in order to address the two biggest problems in the MHS5200A function generator: sine wave harmonic distortion, and square wave ringing/overshoot.

If you want to make the same modifications, here is the Digikey BOM. Note that the capacitors and inductors I used for the Bessel filter were 0402, while the pads on the PCB are 0603; either size fits, though 0402’s are obviously a bit harder to work with.

See the pictures below for more details.

Board Overview

Board Overview

Replacing the AD812 with the THS3092

Replacing the AD812 With the THS3092 (Be Sure to Replace the Heatsink!)

Modifying the DAC Filter(s)

Modifying the DAC Filter(s)

Bessel Filter Components

Bessel Filter Components

Quadrature Mixers

I’s and Q’s and negative frequencies, oh my! Today we discuss mixers and frequency conversion, in particular, quadrature mixers and Tayloe detectors: what they are, how they work, why you might want one, and what do we use all this I and Q stuff for anyhow?

Additional references:

Description Reference
Introduction to RF mixers Basics of RF Mixers in Radio Receivers, Alan Wolke (W2AEW)
Mixer theory and switching mixer operation Downconversion Mixers, Gino Giusi, Ph.D
Introduction to IQ signals and phasor diagrams Basics of IQ Signals and IQ modulation & demodulation – a tutorial, Alan Wolke (W2AEW)
IQ signal processing fundamentals, Euler’s identities A Quadrature Signals Tutorial: Complex, But Not Complicated, Richard Lyons
IQ phase relationships at positive and negative frequencies IQ Modulation, Keysight Technologies
The Tayloe quadrature detector Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier, Dan Tayloe

MHS-5200A Teardown and Review

After seeing WD5GNR‘s excellent work on reverse engineering the serial protocol for the cheap ebay MHS-5200A arbitrary function generators, I decided to pick one up as a secondary function generator for the lab.

What started as a simple review and teardown video ended with me reverse engineering the entire analog front end to track down the source of some nasty harmonic distortion!

MHS-5200A channel 1 analog front end

MHS-5200A channel 1 analog front end