RF Modules – Pre-certified vs. Non-Certified and How to Design Your Own

RF Modules

If you need to design an RF transmitter into your product, the choice between using a pre-certified RF module, non-certified RF module or designing your own transmitter from scratch is not easy. In this post, I want to persuade you that if you design multiple products containing similar RF transmitters, designing and certifying your own RF module is one of the best ways to save $10,000+ and 1 month time to market per product.

Read on to discover the ins and outs of RF modules and what you need to know to avoid some common pitfalls…

Related Resources:

How to impedance match your antenna
How to verify that your transmitter will pass FCC testing 

RF Implementation Comparison

Here’s a top level overview of the routes you can take to implementing a wireless solution into your product. The ballpark pricing here is for Wi-Fi modules, just to pick an example. The certification costs brackets are wide because they account for variations in regional test requirements and configurations of equipment.

RF Module Comparison

Note that designing your own module really makes a difference to the certification cost and design effort for your next product…. and the one after that…. and the one after than. You get the idea.

What Is An RF Module?

An RF module is a separate circuit board (sub-assembly) that contains all of the circuitry needed to transmit (and usually receive) RF energy. It may include an integrated antenna or a connector for an external antenna. It’s typically shielded to limit unintended emissions and increase EMC immunity. RF modules are typically integrated into a larger embedded system to add wireless communication functionality. There are receive only RF modules and transmit only RF modules, but because most implementations include transmit and receive, that’s what we’ll be covering in this post.

Two of the most widely used RF modules are bluetooth modules and wifi modules. But, almost any transmitter can be a wireless module. It’s important to note that even ‘licensed transmitters’ (transmitters that require the purchaser to get a license to legally use the device) can get modular certification, but in this post I’m going to focus on the most common implementation, which is ‘unlicensed transmitters’ where the purchaser can just buy the equipment and start using it immediately. In FCC terms, that means a transmitter that falls under part 15C thru 15F of the rules.

As I mentioned, some examples of RF modules are bluetooth modules and wifi modules. You can easily add in this functionality into your system by dropping in a module.

Pre-Certified vs. Non Certified RF Modules

When you’re shopping around for a solution, you’ll notice that manufacturers of RF modules offer both pre-certified and non-certified options. Read on below to find out the pros and cons of each option.

Pre-Certified RF Modules

A pre-certified RF module means that the manufacturer has gone to the effort and cost of certifying that particular module. It’s super important to note that the manufacturer must have certified the module in all of the countries or regions that you intend to sell your product, otherwise you’re going to have to get a lab to do a full RF certification anyway to cover the new region.

Pre-Certified RF Modules Upsides

  • Fastest time to market
  • Reduces risk of RF certification to zero
  • Fast integration time into your product

Pre-Certified RF Module Downsides

  • High cost per unit
  • Restricted to antenna type(s) used in original certification
  • Restricted to modulation schemes used in original certification
  • Risk of OEM product shortages

When you use a pre-certified RF module, you’re restricted in your choice of antenna(s). The original manufacturer (OEM) would have provided the EMC testing laboratory doing the RF testing with one or more antennas to certify the transmitter with. Because the antenna type has such a large effect on transmitter behavior and performance, the end customer (you) have to choose an antenna type that is electrically identical to those used during the original tests. The RF module OEM will/should provide you with an ‘integration manual’ that details exactly how the module should be integrated into your device, including the choice of antennas.

In the same way, you’re also restricted to the modulation types that the OEM used during the original certification.

You can search for this information by typing the FCC ID number in the FCC’s search tool. The manual and implementation manual will be visible because it’s publicly available information.

FCC ID search

FCC ID Search Tool >>

The obvious downside for using a pre-certified RF module is the per-unit cost. The OEM charges you a premium (quite rightly) for having gone through the headache of RF certification testing. It can take 4-6 weeks to fully certify a transmitter, and that’s assuming all goes well! And costs can run anywhere from $7k to $20k per transmitter depending on which regions you want to certify and how many antennas/modes of operation the transmitter has. If your goal is fastest time to market, using a pre-certified RF module reduces the risk introduced by wireless certifications to practically zero. Similarly, if your product is low volume and high margin, it may not be worthwhile to fork out for your own transmitter design.

Pre-Certified RF Module Examples

Upverter have compiled a good list of WIFI and bluetooth modules including average pricing, certification regions and a bunch of other useful criteria. Here are the links:

bluetooth RF Module comparison

Picking the right Wifi module >>

Picking the right bluetooth module >>

Non-Certified RF Modules

Non-certified RF modules are exactly the same as pre-certified modules, only the OEM hasn’t put the module through official certification testing. They may well have undertaken their own testing on the device to prove that it is compliant, but you will also need to go through certification. I’ve unfortunately spoken to several companies who already designed in a non-certified module and weren’t aware of this difference. It cost them around $10k and 4 weeks time to market that they didn’t account for.

Non-Certified RF Modules Upsides

  • Lower cost than pre-certified module
  • Reduces risk of RF certification compared to designing your own module
  • Fast integration time into your product
  • Choose your own antenna(s) and modulation

Non-Certified RF Module Downsides

  • Still higher cost than designing your own
  • Reliant on OEM for parts (may go obsolete or have long lead time)

How to Design Your Own RF Module

The FCC has pretty good guidance on how to design your own RF module. The key is to make sure that you’ve ticked all of their boxes.

Probably the first thing to note is that there are 4 different levels of modular certification: single-modular transmitter, limited single-modular transmitter, split-modular transmitter and limited split-modular transmitter. The ‘limited’ options allow for relaxation of the rules at the cost of being constrained to your own host(s) i.e. you can’t sell the module to other people or radically change the enclosure of your design. For this post, I’m going to focus on the Cadillac of modular certifications, the “Single-modular transmitter”, because it’s not that hard to get so you may as well!

Below I’m going to outline the requirements for FCC modular certification:

RF Module Shielding

RF Module shieldingThe radio elements of the transmitter must be shielded. There are a few parts that are permitted to be external to the shield such as PCB antenna (if that’s the type you’re using) and tuning capacitors. But for the most part, all components associated with your transmitter should be housed beneath a shield. This is to limit any emissions from the design. I’ve seen FCC submissions where the OEM has claimed that a ground plane is sufficient for a ‘shield’, and they got away with it. But they must have caught the TCB (the body that issues the certification) on a good day. In my experience I would say not many TCBs would let you away with that.

RF Module Buffered data inputs

The module must have buffered modulation/data inputs. Again this is an attempt to limit emissions for any type of host that the module will be integrated into. I’ve seen many modular certifications that use the justification that the inputs to the RF chip are buffered so therefore external buffers are not required. If you want to avoid any doubt, drop in some cheap data buffers.

RF Module Power Supply Regulation

The module must contain power supply regulation on the module. Again, this is an attempt to ensure that emissions are contained when integrated into all hosts. Many RF solutions provide an on-chip regulator for powering a part of the transmitter circuitry. Depending on your solution, you may or may not need to include a separate external regulator for the RF module.

RF Module Antenna

Bluetooth RF ModuleThe module must contain a permanently attached antenna, or contain a unique antenna connector, and be marketed and operated only with specific antennas. If you’re not including a permanently attached antenna, you can see that the FCC wants you to use a ‘unique’ antenna connector. This is an attempt to make it difficult for the end user to use their own type of antenna. Ironically, antennas that fit the ‘unique’ connectors are now easily available from companies like digikey. Connectors such as “SMA-RP” are considered unique, but not “SMA”.

The RF module must demonstrate compliance in a stand-alone configuration

This just means that the EMC lab will need to test the module on its own. You can provide support hardware such as a carrier board or auxiliary debugging equipment, but the module should not be within a host device for testing purposes.

The RF module must be labelled correctly

With your certification application, you need to include a diagram or photograph of the FCC ID number affixed to your module. It can also be displayed electronically if you like.

The RF module must comply with all specific rules applicable to the transmitter

If for instance you have a 2.4 GHz transmitter that falls under 15.247 of the rules, then you need to test the module to 15.247. This is no different to the requirement for a non-modular certification. With your application, you need to provide the test report that shows compliance with the rules.

The module must comply with RF exposure requirements

This is also a requirement for a non-modular certification. It means that the maximum field strength of the product will be evaluated and compared to government RF exposure limits. The EMC test lab will do this. For most wireless products, this is just a calculation in a spreadsheet and isn’t a problem for most low power transmitters. But, if you expect your transmitter module to be warn in close proximity to the human body, you may also need to undertake SAR (specific absorption rate) which can easily run you $5k+. SAR testing is usually required for things like cell phones and laptops. There are exemptions depending on how powerful the transmitter is and how close to the body your device will be placed. Contact a SAR testing lab for more info.

For more guidance on designing an FCC compliant RF module, see KDB996369 and this presentation.

Connectors

RF Module HolesYou needn’t even use connectors on your module. You can use half holes and solder it directly to your circuit board, so the increase in cost of an extra PCB is minimal. Make sure to clear the board of tracks and vias below the RF module to avoid potential shorts.

RF Module Documentation Requirements

When you design your own RF module, there are some differences in the documentation requirements you need to take care of. This example is for the FCC, but similar rules apply to different regions around the world.

Extra documents you need to produce:

1. An integration manual

This is required to show your customer or your own engineers how the module should be implemented. It includes information such as antenna choices and labeling requirements that they should use on the host product.

2. Labeling

The FCC’s labeling requirements are slightly different for product that contain wireless modules. The module itself needs to be labelled with the FCC ID number and on the outside of the host product, the label need to include text such as: “Contains Transmitter Module FCC ID: ABC12345” or “Contains FCC ID: ABC12345.” The rules for this can be found in part 15.212.

When NOT to design your own RF Module

There will be some cost trade off involved with this choice. If your predicted sales volume is low and your margins are high, then designing your own module may not be the way to go. Also, if your product is a one off design and you don’t think you’ll ever need an identical transmitter again, there’s no point creating your own module.

If you want to dig more into the cost analysis of pre-certified modules, I highly recommend Texas Instrument’s app note on the subject.

There is negligible cost difference in certifying a module vs. certifying a transmitter within your product, so if there’s even a small chance that you’ll need the same radio for future products, I’d recommend going with the module.

RF Modules FAQ

Can I Copy a Pre-Certified RF Module to Avoid Certification?

Unfortunately not. The reason is that the certification is granted only to the manufacturer of the module. They are responsible for ongoing compliance of the modules so therefore, if you copy their module design (even if they give you the schematic and layout), they no longer have the power to verify that the modules continue to be in compliance. On the face of it, this seems like an unnecessary and costly extra step that the regulatory bodies put in place. I’m normally against unnecessary regulations and testing requirements that seem too stringent, but this time there’s actually some logic to it. Say you copy the schematic and layout of an RF module. If you change something crucial by accident, such as the PCB stack, that can totally change the characteristics of the RF transmitter. You can no longer guarantee that the transmitter is compliant with the rules. This is why copying a pre-certified module design doesn’t mean you have a certified device.

What if I ship around the world?

If you are designing a pre-certified RF module into your product, make sure that it has all of the global certifications that you need. Wireless regulations are different around the world, so if your module only has FCC certification, that doesn’t mean you can ship your product to Europe or Japan. To ship to different regulatory zones, the module would need to be pre-approved for those particular zones.

With a pre-certified RF module, do I need to still do other emissions testing?

Yes. You still need to have your product tested for unintentional emissions associated with the non-transmitter circuitry in your design. This process is much less painful – only 1 or 2 days if all goes well, and $1k-$2k costs. If you need immunity testing, that would be extra, but your product is essentially treated as a product without a wireless transmitter in it.

 

Wrap Up

This post was aimed to give you the low down on wireless modules options. I hope you have a clearer picture of which route to take! Let me know if you have any questions in the comments.

 

Cheers,

Andy.

18 Comments

  • Mike Russell

    Reply Reply November 24, 2014

    Thanks for providing this article. It was excellent. I have a question concerning using a pre-certified module. When using a pre-certified module the article says that the certification risk is zero. Does that mean that when performing emission and immunity testing that you perform this testing with the pre-certified module either off or not in the product that is undergoing testing because otherwise I think that there would still be some risk.

    Thanks,
    Mike

    • Andy

      Reply Reply November 24, 2014

      Hi Mike, if you’re using a wireless module that has already been assessed for compliance with the R&TTE directive, that compliance may or may not be transferred to your product depending on the way you purchased it and the way you use it. This guidance document outlines your responsibilities as a manufacturer for integration of module into your product (http://www.rtteca.com/TGN01%20-%20May%202013.pdf). Adhering strictly to the rules, it is possible that even if the module is ‘pre-approved’ for use in Europe, you will also need to have your final product tested to wireless, safety and EMC standards. See ETSI TR102 070-1 (http://www.etsi.org/deliver/etsi_tr/102000_102099/10207001/01.02.01_60/tr_10207001v010201p.pdf) for more details.

      In reality, I think many manufacturers do not re-do the RF and safety portion of testing when they use a module that has been tested to the R&TTE directive. Ask an accredited lab for advice on your specific case, and if you need a legal opinion, chat with an NB (notified body). Hope this helps!

  • vince

    Reply Reply December 23, 2014

    Nice one Andy 🙂
    Thanks for your post!

    • Andy

      Reply Reply December 23, 2014

      Cheers, no problem Vince.

  • Ben

    Reply Reply August 12, 2015

    This was a good jump start to identify our research tasks. Thanks!

    How can I get my hands on more information in terms of antenna options (omni, patch, directional, etc) and the associated FCC pitfalls or trade offs in a low power 802.15.4 architecture?

  • harut H

    Reply Reply September 4, 2015

    Hi My question is about royalties associated with using wifi or Bluetooth. When using pre-certified or non-certified modules do we have to pay royalties to Bluetooth and wifi
    Thanks again for the article

  • Jasper Sikken

    Reply Reply January 12, 2016

    Hi,
    In our product we have a wifi-radio with our own PCB antenna and a BLE module separated 5 cm from each other. Only one radio is ON at a time. The BLE module comes with onboard chip antenna and already has FCC certification for intentional emissions. The wifi transmitter does not have FCC certification for intentional emissions. Do I need to perform intentional emissions test on the BLE module?

    • Andy

      Reply Reply January 13, 2016

      If you’re using the BLE module as per the original grant of authorization (i.e. same antenna, max gain, freq band, modulation etc..) then I don’t believe you need to have the RF retested. If they were both on at the same time, you’d need to do some re-testing due to antenna co-location. So you should just need to do unintentional emissions for the device, plus an RF certification of the Wi-Fi Tx. Always ask an accredited lab though for confirmation.

      If you want a process to verify your Wi-Fi RF before certification, check out my FCC RF pre-compliance course: http://emcfastpass.com/training/index.php/course/fcc-wireless-pre-compliance/

      Also, we have an antenna matching course coming up soon too: http://emcfastpass.com/training/index.php/course/antenna-matching/

  • pazcal

    Reply Reply May 8, 2016

    High Andy,
    Thanks for this very interresting article. I have a question, and I cannot find any answer about it on the web.
    So I would like to develop several products, all incuding bluetooth Low enregy radio. Regarding the quantities, and the target price I will develop my own BLE solution with an NRF52 chip. Furthermore for size (very thin casing) and price reasons, I cannot use a separate module, and I must integrate the radio part on the motherboard PCB of all the products.
    So If I design a “module like” radio that is integrated on the motherboard (not solded on it, but as part of the motherboard), can I certified (FCC, CE, ARIB, …) this PCB part, and reuse it in other products?
    The goal is to design a unique module (that will be certified) and reused in all my products so that I take benefit of initial certifications (FCC, CE, Arib, …). The module-like will belong to all product motherboards.
    Not easy to explain, I hope my question is clear enough
    Thanks in advance
    regards
    pazcal

    • Andy

      Reply Reply May 15, 2016

      Hey Pazcal, unfortunately what you’re describing is just a regular transmitter circuit. According to the FCC, “Modular approvals are for tangible, clearly delineated, devices that operate when installed within, or attached to, a host.”

      Additionally, “Single or limited-single modules and the RF front-end section of a split or limited-split module must be a separate physical assembly that can be installed into (or attached to) a host as a separate subassembly (daughter-board sub-assembly).”

      You might want to investigate limited modular approvals which allow relaxation of some of the modular approval requirements at the cost of requiring full control of the manufacturing process (i.e. you can’t sell to a 3rd party). See my video on the subject: https://emcfastpass.wistia.com/medias/3rwukvgdc7 (taken from the RF precompliance training program: http://emcfastpass.com/training/index.php/course/fcc-wireless-pre-compliance/

      “I cannot use a separate module, and I must integrate the radio part on the motherboard PCB of all the products.” – If you’re trying to minimize certification impact, I would recommend you revisit this design constraint. You could even consider soldering your transmitter module directly to each motherboard (no connector needed), so your cost would only increase very marginally.

      Good luck!

      Andy.

  • Mike

    Reply Reply June 16, 2016

    Andy,

    Very nice article. Thanks and well Done!

    I have a question concerning the use of pre-certified modules.

    In our application I am intending to use two pre-certified modules: one Wi-Fi module and one BT module (from two different vendors). Each module will utilize the approved/certified antenna appropriate to the module (they happen to be the same).

    If I install both modules into my system – with an external 4″ antenna on each of end of my product (about 9″ apart) will this still be certified or will this somehow de-certify the use of one or both modules?

    Thanks for your expert input!

    Mike

    • Andy

      Reply Reply June 20, 2016

      “Antenna co-location” generally voids existing FCC modular certifications without additional testing. Antennas are co-located if they are within 20cm of each other and both transmitters can operate simultaneously. If the antennas are further than 20cm apart or if they don’t operate simultaneously, then my understanding is that the modular certifications remain intact and you don’t need to worry about any further testing (always ask an accredited lab for confirmation).

      If antennas are co-located, you can probably do a class II permissive change if the module vendors agree which is a lot cheaper than getting a full certification.

      For clarification for your specific scenario, I would always ask a couple of TCBs (to make sure their advice is in sync) or send a query directly to the FCC OET.

      Andy.

  • Justin

    Reply Reply June 21, 2016

    Thank you so much for this article.

    Is there any regulatory limitations for selling a board-only device to be compatible with another manufacturer’s pre-certified module? That is, my design, as sold by me, does not include an RF device, requiring only unintentional emissions testing. However, my design includes space for the end user to install a pre-certified or un-certified module that is purchased separately from another manufacturer. Would I still be required to gain certification for my device with the “optional” module installed?

    Thank you for your time.

    Justin

  • Erik Sternå

    Reply Reply October 10, 2016

    Hello and thank for a great article!

    I’m developing a product which will feature a pre-certified wifi module. Our projected sales are very low and and it would just no be feasible to design our own module.
    My question is the following: We would like to ship the product worldwide. As I understand, I should choose a pre-certified module with certifications for as many countries as possible. Which certifications are “enough” for which markets? I know FCC is good for USA and Canada, CE is good for all Europe and South Korea and Japan have their own. If my module isn’t certified for some of these regions, but for the other (say it lacks certification for South Korea), how hard it is to certify for only that specific region, given that it has passed for the others?

    Cheers
    Erik

    • Andy

      Reply Reply October 12, 2016

      The answer to this can be very different on a per-country basis and it changes often. It’s an intricate subject that you can spend a lot of time on. Sometimes the technical requirements are different for different regions (e.g. different bands and channels are allowed) and sometimes it is documentation issues that are the limiting factor – such as products entering China must be tested within China.

      I would contact an expert at a large lab group such as NTS, Intertek or Trac for details on the specific regions that you plan to import your product to.

      Also, I would challenge you to focus on larger opportunities where the cost of a $10k certification is minimal compared to the sales volume your product generates. I’m all for entrepreneurialism, but why not focus your engineering effort on a product that makes the certification fee look like chump change?

  • Kevin

    Reply Reply November 19, 2016

    Hi Andy,

    Thanks for the article. With the upswing in IoT interest, wireless modules are bound to increase in popularity.

    I have a quick question about testing products with multiple transmitters. Assuming two radios are in use and will be simultaneously transmitting, what is involved in testing with simultaneous transmission (or colocation) In particular, what tests need to be performed on the unit with respect to radiated emissions? Would one sweep with both transmitters set to a middle channel be enough or would they need to be tested using various combinations of channel settings? I’ve read through the FCC docs but haven’t anything conclusive.

    Thanks for any insight you can provide.

  • Angela

    Reply Reply December 9, 2016

    Hi Andy,

    Thanks for the detail article. I am interested in what engineering teams would do different at manufacturing EOL test when the select:
    a) Select a Precertified RF module (BLE module) that is sold as a SOM. Would the EOL test in the manufacturing line retest signal strength of transmit , etc or just test pairing to check that the manufacturing of SOM to PCB is sound?
    b) If one were to design their on Bluetooth chip onto the PCB what would be the different in the EOL test?

    Any pointer would be much appreciated.

    Thanks,
    Angela

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