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Diode Ring Mixer Kit

YooFab™ Schottky Diode Ring Mixer

YooFab™ Schottky Diode Ring Mixer.#

YooFab™ Diode Ring Mixer

Main properties#

The YooFab™ diode ring mixer, once correctly built, will provide an extremely sensitive three port frequency-mixer module that operates across all HF bands.

  1. The kit was designed using Barefoot-Power for optimal success.

  2. This module does not need power connectors, as it is a passive circuit.

  3. The circuit is a hybrid mixer design which owes some characteristics to a single balanced mixer, while other features derive themselves from a typical double balanced mixer topology.

  4. The circuit functions as a double balanced mixer.

  5. The style of PCB supplied is popular with many RF design engineers.

Component List#

bom GEOFF - ​MØOOZ (AKA Zorgrian) — YooFab™ / CC BY NC ND

Very mild-mannered warnings

The colour / style of some hardware components like pins or connectors may vary.

Warning: on the picture, the PCB hasn't been etched yet.

Name Value Quantity Notes
C1 C2 10pF 2 Disk Ceramic Capacitor
C3, C5, C6 100nF 3 Disk Ceramic Capacitor
C4 10nF 1 Disk Ceramic Capacitor
D1, D2, D3, D4 BAT42 4 Schottky diodes
4T:10T Impedance Transformer FT37-43 1 https://www.micrometals.com
TRIMMER Potentiometer 200 Ω 1 POT
Copper wire 33SWG 40 cm in length
Printed Circuit Board 1 Vinyl protected copper
35 mm stand-off 4 Black plastic
M3 screws 4 Black plastic
RCA (Phono) connector 3 Gold Plated
Decal Sticker 1 To put on the PCB (non component side)
Polystyrene piece 1 To organize your components

Circuit Diagram#

GEOFF - ​MØOOZ (AKA Zorgrian) - YooFab™ / CC BY NC ND

Circuit Operation#

Help provided by ONNO - PA2OHH

ONNO - PA2OHH kindly carried-out extensive experimentation while Barefoot, during the ice-cold winter. His quest was to find the best ratio for the Mixer-Transformer. This endeavour included:

  1. Swapping round the Transformer and the building of a 1:1 ratio Transformer.

  2. The conclusion of this building and testing, was that on receive either swapping round the transformer or making a 1:1 version, marginally increases the base band output.

  3. However, when using this mixer to transmit DSB-RC, the present design is better, as otherwise a weak modulated output results. He has also suggested different values for the Audio Coupling Capacitor, which results in a far better output on receive. His wisdom and modifications are gracefully accepted and have now been incorporated into the new YooFab™ mixer kit.

A ring of diodes#

This circuit takes the shape of a ring of Schottky diodes; hence the 'name' Diode Ring Mixer.

The circuit looks like a bridge rectifier, except that instead of diodes alternately connected cathode to cathode then anode to anode, the diodes are all connected anode to cathode.

In this design, the Local Oscillator (LO) is fed into a 200 Ω (200R) Potentiometer (POT). This is a preset type POT as it only needs setting once. The LO signal, which after passing through the 100nF capacitor, alternates between positive and negative current. This causes one pair of diodes to conduct, while the other pair are reverse-biased. This is called commutation.

The two ends of the POT are currently decoupled with 10pF capacitors. However, this has been found unnecessary and is removed in the 2021 version.

The upper and lower current paths connect to the 4 turn end of the transformer. The diodes see a DC path to ground, on both the upper and lower sides of the diode ring; this is seen on the right-hand side of the diagram. This, is fundamental to this circuit's operation. Note that the LO port is not intended to be bidirectional.

The Audio in/ out port is the junction of the 100nF (replaced with 1uF) capacitor and the 10nF capacitor that goes to ground from the diode ring.

When used within a receiver configuration, audio appears at this port, which may feed into the YooFab headphone amplifier or other sensitive amplifier.

Three Ports definition#

  1. Local Oscillator: the signal level of the LO may be anywhere between 447mV (p-p) and 1.736 V (p-p). When used for radio reception, the voltage level at the LO port does provide scope for adjustment in the reception of weak and strong signals. A good starting place is 1V (p-p).1 Note that this mixer is very robust and will not be damaged when fed with anything up to 20 Volts! Having said this, it will not function better at higher voltages; indeed, the mixer functions best at the lowest voltage that will assure the diode are in commutation. 1

  2. RF in/ out (bidirectional): The blue coloured glass Schottky diodes used, permit this mixer to detect low signals when used as a receiver. It is possible to connect an antenna directly to the RF in/ out port. Using an audio amplifier such as the YooFab Headphone amp, SSB, Morse, and AM may be heard from the signal at the Audio in/ out port.

  3. Audio in/ out (bidirectional): This port of the mixer allows input or output of audio frequency waves. When used in a receiver, this port will output Audio from SSB CW or AM signals appearing at the RF in/ out port. With Audio injected into this port, together with a LO frequency at the Local Oscillator port, then the RF in/ out port produces a Double Sideband Reduced carrier (DSB-RC). Through this port, it is possible to listen to SSB, Morse, AM using an audio amplifier like the YooFab ™ headphone amplifier. Alternatively, and without amplification, the Audio in/ out port may be connected directly to the microphone input of a computer. Subsequently, FLDIGI, WSJTX and other programs may be used to recover digital modes with a high successfulness.

The Local Oscillator (LO) peak to peak (p-p) voltage range needed by the RFLEGO diode ring mixer.

Volts LO pp GEOFF - ​MØOOZ (AKA Zorgrian) — YooFab™ / CC BY NC ND

Signals at the RF port#

Here we look at signals that may be produced at the RF output port of this mixer.

In both pictures below, the Orange coloured trace is the signal at the RF in/ out port, whereas the Green coloured trace is the signal at the Audio in/ out port.

Both Audio and RF ports are bidirectional, such that signals may be INPUT or OUTPUT from these ports.

The DSB-RC waveform#

  1. The output has a characteristic slanted modulated waveform.

  2. The waveform shows that both the negative and positive going parts of the Audio input appear as separate modulation envelopes.

Double Side band Reduced Carrier DSB-RC

GEOFF - ​MØOOZ (AKA Zorgrian) — YooFab™ / CC BY NC ND

The AM waveform#

  1. This mixer may also be used to produce a simple amplitude modulation (AM) waveform. The picture below shows this.

  2. It is achieved by unbalancing the mixer such that the Potentiometer is moved toward one or other extreme of its travel.

  3. Compare the above DSB-RC waveform with the picture below, where we see that negative going Audio produces a 'narrowing' of the amplitude, whereas positive going Audio produces a 'widening' of the amplitude.

  4. Note that the use of a diode ring mixer, is certainly not the most elegant nor the least problematic method of Amplitude Modulation. (AM)

The diode ring Mixer configured to produce AM

GEOFF - ​MØOOZ (AKA Zorgrian) — YooFab™ / CC BY NC ND

Instructions and a good deal more#

Click HERE for assembly instructions in SPANISH.

Click HERE for assembly instructions in ENGLISH.

Here you can follow the construction sequence:

GEOFF - ​MØOOZ (AKA Zorgrian) — YooFab™ / CC BY-SA

GET THE 2021 VERSION OF THIS KIT#

If you are interested in this kit, email:

anna@yoofab.com

FOOTNOTES#

  1. The subject of which is the best way to use diodes is thoroughly thwarted with issues and is non-trivial. However, 1. Your ears are a good test of this on reception. 2. To GEOFF - ​MØOOZ (AKA Zorgrian), at least, it makes sense that we do not want to massively thump more voltage than is needed to make the diodes commutate. Necessarily, this will overdrive the PN-depletion zone of signal diodes, creating variations of capacitance at every peak and trough of the Local Oscillator. The net effect of this may be the production of more unwanted and very unpredictable harmonics, which is intensely undesirable. However, GEOFF - ​MØOOZ (AKA Zorgrian) designed this mixer using BAT42 Schottky Diodes, which is a diode formed by the junction of a semiconductor with a metal, having an average forward voltage of 0.447 V; thus there is no typical PN junction. Yet, there is 7pF capacitance @ 1V. A Schottky diode has a low forward voltage drop and a very fast switching action. ↩↩