How to Select & Buy the Best RF Mixer

Selecting and then buying the best RF mixer for any RF design involves looking at many parameters and balancing them with the cost best pace to buy them.

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When involved in any RF design process, it is quite likely that an RF mixer will need to be specified and bought as they are one of the key building blocks for many designs.

As the RF mixer performance will impact on the performance of the whole system, more than most other components, it is essential that the right mixer is selected and bought.

various RF mixer circuits and images to illustrate page on how to by the best RF mixer

The selection of the right RF mixer will obviously depend on its basic specification, but other factors are also important: whether a connectorised mixer is needed, IC based mixer, discrete components, cost is another major issue as is its availability, and the source: whether it is available via a distributor . . . all these factors and many more must be considered.

The overall decision is a balance of many factors, some of which are associated with the basic specification of the mixer, whereas others may not be. Electronic circuit design engineers need to be aware of all aspects of the particular component or mixer circuit when selecting which component or which approach to adopt.

Commercial or in-house design

One of the firs decision to be made when selecting the best mixer for a given RF design is whether to use a commercially made mixer or whether to design on as part of the overall circuit design.

Typically mixers using discrete components will not perform as well as many of the mixer blocks that can be bought - these may be within a connectorised mixer unit, or as an IC, Many integrated circuit mixers offer very high levels of performance and the costs are not as high as many other options.

For some applications, separate connectorised mixers may be appropriate. These may be particularly good for some microwave applications where other components are contained within blocks with connectors.

This decision will reflect and affect the whole approach taken for particular RF circuit design.

Another early decision to be taken when choosing an RF mixer is whether to adopt an active or a passive mixer. Active mixers use active components and generally have a conversion gain where the output signal level on the new frequency is higher than the input signal frequency signal, whereas passive mixers will have a signal loss - often around 6 or 7 dB.

Many passive mixers use diode rings and input and output transformers, and they can exhibit very high performance in terms of spurious signals. However the conversion loss will reflect in the noise figure and means that higher levels of gain may be needed before the mixer stage.

These days, many IC based active RF mixers perform just as well, if not better than the passive ones, and the cost can be less, so it is well worth investigating he marketplace to see what is available before adopting a particular approach.

Mixer package style

A major decision to look at when selecting the best RF mixer to buy for a given RF design is the style of package. This includes many aspects from the size to the way it is fitted and similar considerations.

There are many options to consider and these will have a major impact on any design.

Connectorised packages: Some RF mixers, particularly those aimed at use in microwave systems where RF mixers might be mounted along with a number of other items that are interconnected using coax. These will all have connectors so that they can be easily incorporated into the system. When considering this approach and selecting the connectors, remember that the connector type will need to be chosen, ideally matching that of the other connectorised components like circulators, filters, etc. Also remember that interconnecting leads will need to be factored into the design in terms of loss, etc and also the cost of these will need to be considered.
PCB through hole mounting: Through hole mounted RF mixers are widely available. These may be in normal IC packages such as the dual in line IC packages, but other formats are also available. When selecting the required mixer remember that it must be easily fitted to the PCB and also the size will need to be considered as some non-IC style packages may be taller than the IC ones.
Surface mount package: Many IC based RF mixers as well as other types like the passive mixers are available in surface mount packages or surface mount devices. These can be ideal when RF and microwave electronic components are all mounted on a PCB, sometimes with interconnecting stripline feeder, etc.

It is important to finalise the decision about the style and mounting of the RF mixer before moving onto other decisions about the actual performance specifications, etc. The package will govern many aspects of the actual choice later.

Other functions

Many RF mixers, and particularly those based within ICs can offer additional capabilities. Some RF mixer ICs offer capabilities like an incorporated local oscillator, a sub-harmonic mixer feature, image reject mixers and the like.

When selecting the mixer and looking at the marketplace, it is well worth checking to see whether additional functionality that might be needed can be incorporated within the IC or other package. This will most likely significantly save on costs and simplify the RF design.

RF performance specifications

Obviously the RF performance is an important element of deciding about the best RF mixer for the particular RF design. However once the basic decisions about the format of the RF mixer have been made, then the performance aspects can be added and the final decisions about the specific part can be made.

RF mixer circuit symbol showing the RF, LO and IF ports

Some of the key RF performance parameters and specifications that will be used in making the decision about the best RF mixer include those int he following list:

Frequency response: One important aspect of the technical specification for the mixer is its frequency response. Even though most RF mixers cover a wide bandwidth, when looking to select the best mixer for the particular RF design, the frequency coverage will be a major consideration, slimming down the options from which to choose.

Typically an RF mixer will be specified to operate over a particular band, or up to a top frequency. The bandwidth for the mixer must accommodate the frequencies which it is expected to encounter
It is normally good practice to allow a margin so that the performance of the mixer will fully meet its operational requirements easily over the complete range and not start to fall towards the extremes of the requirements.
Mixer local oscillator level: The local oscillator or LO input level is another key parameter to be considered.The higher the local oscillator input level, the higher the RF level that can be accommodated without running into issues with distortion, etc. Typically the local oscillator input should be 10dB above the highest anticipated RF signal. This keeps the mixer running within its linear operating range.
1dB compression point: All RF mixers have limitations on the RF signal levels they can handle. The 1dB compression point is an indication of the level the mixer can handle without undue levels of distortion being introduced.
Balanced or unbalanced: Mixers come as balanced or unbalanced types. Unbalanced mixers will have large levels of the input signals appear on the output as well as higher levels of leakage between the ports. In many instances it is advisable to minimise the levels of unwanted signals as these can easily give rise to spurious signals being generated and appearing on the output.
Third order intercept: The third order intercept point of an RF mixer can be important when high level signals need to be handled. The figure gives an indication of the levels of mix products that will occur on signals entering the RF port of the mixer.

There are many other aspects and parameters associated with RF mixers and their performance which need to be considered when making a decision about the best RF mixer to select and buy for a particular RF design.

Read more about . . . . RF mixer specifications.

Reliability

Reliability is an issue that is at the centre of even electronic circuit design. Reliability figures will be available for many of the higher priced mixers, especially those associated with military and aerospace applications.

These figures may be of great importance when selecting the right RF mixer. For those that are not specified, it is worth buying product from a trustworthy manufacturer as they are unlikely to sell second rate product. That said most ICs and other solid state components have very high levels of reliability. Often the main issues are soldered joints and mechanically related issues which would not be an issue with an IC. Some of the packaged RF mixers may have lower levels of reliability.

Cost

Cost is a key issue for any RF design. With a lot of equipment now being very cost sensitive, it is essential to ensure that the cost of the components used are key to a minimum within reasonable limits.

Looking at all the alternatives may help reduce the costs, and the purchasers may also be able to negotiate some good prices, especially with established suppliers and if quantities are large enough.

Availability

Component availability can be a very important issue these days. Lead times can go up and down considerably dependent upon demand. After the COVID pandemic of 2020, component lead times extended to very large times as manufacturing started up again, and the component manufacturers, especially IC manufacturers got their manufacturing facilities fully back to operation and demand rose.

When making a decision about the best RF mixer to select and buy for an RF design, it is always worth checking on the current availability, and also to see what the expected availability is likely to be over the production and maintenance life of the product into which the mixer will be incorporated.

Second source

Electronic components are always going out of production as newer lines are launched. However this can make keeping a product in production over a period of time more difficult. It also creates issues for the longer term maintenance of products.

Although many RF mixers tend to be electronic components that are specific to one manufacturer, it is always worth checking whether it is possible to find a second source, or a second mixer that might fit the form and function of the main item. In this way, if one product ceases to be produced there is a greater chance of being able to source new mixers that do not require a re-design of the circuit.

Manufacturer

It is often beneficial to select a mixer, or any other electronic from a recognised manufacturer, especially for items being produced n a large scale. Although it may be a little more expensive there can often be significant benefits in terms continuity of supply, quality of the product, conformity to the published specification, etc.

While it may be acceptable for home construction to use product from almost anywhere, having a traceable source can be a major issue of RF design and manufacturing organisations.

Availability through a distributor

Using electronic components distributors can be a very useful approach. Component distributors are very useful as they can help procure product when there are issues with obtaining them. They carry stock of very many items, and they can assist in scheduling the delivery of the electronic components of all types when they are needed.

The use of electronic component distributors also significantly reduces the number of suppliers in a production environment and this has many benefits for any production organisation.

Selecting the right RF mixer for any RF design is an important decision. It can affect the performance of the whole product in terms of its performance as well as the ease with which it can be manufactured. There are many decisions to be made when selecting and buying the right RF mixer including its performance as well as where to buy it from, its format and many other aspects of the particular mixer.