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Project Notes

#327 Mixers/RFDiodeRing

A diode ring double-balanced frequency mixer.

Build

Notes

My build here is inspired by another great tutorial from w2aew - #167: How a Diode Ring Mixer works | Mixer operation theory and measurement.

Section 5.2 of Experimental Methods in RF Design includes a complete evolution of the diode ring mixer and a very clear explanation of how it works.

See LEAP#326 for my notes on mixer theory and types.

How it works

  • the RF input is connected to the IF via a transformer
  • the transformer-isolated LO switches the conducting diode pairs on each each half of the cycle, thus the polarity of the RF signal to IF
  • classic example of a commutation mixer

Performance

Test 1: 7MHz LO + 10MHz RF

This works pretty well, alough my signals are quite noisy.

Scope Channel Signal Detail
CH1 LO 7MHz 0.8V p-p
CH2 RF 10MHz 0.4V p-p
CH3 IF  

scope_test_1_td

scope_test_1_fft

Test 2: 5MHz LO + 10MHz RF

With the LO as an even factor of the RF signal, I’m seeing what I’d expect here: very strong sum and difference signals and no other products

scope_test_2_td

scope_test_2_fft

Test 2: 18MHz LO + 2MHz RF

With the LO and RF frequencies separated significantly, sum and difference are strong over other products.

scope_test_3_td

scope_test_3_fft

Construction

I’m using 1N5711 small signal schottky diodes (as did w2aew), which are well suited to this application:

  • high breakdown, low turn-on voltage and ultrafast switching
  • primarly intended for high level UHF/VHF detection and pulse application with broad dynamic range

For the transformers, I’m using 68-26 iron ferrite toroids with 30AWG solid wire (10 turns per winding).

Schematic

RFDiodeRing_layout

Build

Credits and References

About LEAP#327 RadioMixers

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

Project Source on GitHub Return to the LEAP Catalog
About LEAP

LEAP is my personal collection of electronics projects - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting.

Projects are often inspired by things found wild on the net, or ideas from the many great electronics podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know or send a pull-request.

NOTE: For a while I included various scale modelling projects here too, but I've now split them off into a new repository: check out LittleModelArt if you are looking for these projects.

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