A diode ring double-balanced frequency mixer.
My build here is inspired by another great tutorial form 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
Test 1: 7MHz LO + 10MHz RF
This works pretty well, alough my signals are quite noisy.
|CH1||LO||7MHz 0.8V p-p|
|CH2||RF||10MHz 0.4V p-p|
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
Test 2: 18MHz LO + 2MHz RF
With the LO and RF frequencies separated significantly, sum and difference are strong over other products.
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).
Credits and References
- LEAP#326 Mixers - my notes on mixer theory and types
- Experimental Methods in RF Design - chapter 5.2
[#167: How a Diode Ring Mixer works Mixer operation theory and measurement](https://www.youtube.com/watch?v=junuEwmQVQ8) - w2aew
- #166: How to wind a trifilar toroid transformer for a diode ring mixer - w2aew
- 1N5711 datasheet
- ..as mentioned on my blog