Radio Frequency (RF) & Wireless Design

Since the earliest days of radio communications development the need to transfer information (codes, voice, text, video, and data) over radio waves relies on the transposing of one signal (typically a lower frequency) unto another of higher frequency.

https://en.wikipedia.org/wiki/Radio

Since it is difficult and not practical to transfer information over multiple higher frequencies at once, in the early days a chosen higher frequency was used; the was and is called the carrier frequency. It is the frequency of radio transmission.

https://en.wikipedia.org/wiki/Heterodyne

The process of taking a lower frequency and superimposing it onto another is called heterodyning and usually was just the single tone of the code (e.g. 3 KHz) onto a higher frequency (e.g. 3 MHz). The device that does this is called an RF Frequency Mixer :

https://en.wikipedia.org/wiki/Frequency_mixer

At higher frequencies above audio (Super-sonic) this becomes more difficult and tuning the incoming signals against the oscillator to match them requires additional skill. As such there is a better way that was developed (albeit more complicated and expensive at the time) called Super(sonic) heterodyning, which matched the incoming tuner to the voltage controlled oscillator (VCO) : https://en.wikipedia.org/wiki/Superheterodyne_receiver

Mixers can be created using coils and transformers (passive devices), diodes (active devices), or transistors (active gain devices) that provide better signal selectivity and better noise rejection with each progression.

The mixer has usually 3-ports of which each may be single-ended or differential :

• Radio Frequency (RF) Input
• Local Oscillator (LO) or VCO input
• Intermediate Frequency (IF) output

Diode mixers can be classified as either :

• single diode mixer
• single balanced mixer (one balun)
• double balanced mixer (two baluns)
• triple balanced mixer (three baluns)

One of the most popular Double Balanced Diode mixers is from mini-circuits as their SBA series for low cost prototyping:

https://www.minicircuits.com/WebStore/Mixers.html

Transistor mixers can be created with either JFET, bipolar, or MOSFET transistors, with the most common form as a Gilbert Cell :

https://en.wikipedia.org/wiki/Gilbert_cell

This type of mixer was used in the low cost commodity mixer/vco device manufactured by Phillips as the NE602 which was later as the NE612 for 0 to 70C devices. the SA602 or SA612 are extended temperature devices but of the same design characteristics :

https://en.wikipedia.org/wiki/NE612

So if you have any questions about RF mixers, be sure to post them below.