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I see that some wireless devices like Bluetooth speakers don't use shields like this one

enter image description here

but some do. My understanding of FCC Part 15 is that only modules need shields. So how come some devices use shields whilst others don't?

Thanks

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In the United States the FCC (Federal Communications Commission) Part 15 regulates unlicensed transmissions.

It doesn't matter whether you are using a "module", it is the unlicensed use of any transmission.

The FCC doesn't care HOW you comply with the regulations. If a device complies with regulations without using a shield, so much the better.

Fair article regarding FCC Part 15

(Shield meaning here is a metal envelope or enclosure, not shield as used in Arduino definitions)

EDIT 1 : A device manufacturer might also use shielding to make their product more immune to interference from other electro-magnetic interference.

EDIT 2 : After seeing comment by DigitalNinja, I did further research. Apparently the FCC does use the terminology "module" and "modular". The following is extracted from : October 23, 2015 TRANSMITTER MODULE EQUIPMENT AUTHORIZATION GUIDE :

One definition of modular is cited, among many other types of modular as,

Single-modular transmitter is a self-contained physically delineated component that can demonstrate compliance independent of the host operating conditions, and complies with all eight requirements of the Section 15.212(a)(1) and summarized below.

Further quoting,

and which complies with all eight requirements of § 15.212(a)(1).

Which includes as the first item :

1) The radio elements must have the radio frequency circuitry shielded. Physical components and tuning capacitor(s) may be located external to the shield, but must be on the module assembly; 2) The module must have buffered modulation/data inputs to ensure that the device will comply with Part 15 requirements with any type of input signal;

There are other sections of the same "Authorization Guide" that allow compliance with the FCC Guide without using shields. Often regulations can conflict with themselves. I can now see where the original OP, and the commentor DigitalNinja have concluded a shield is necessary, even though I read the FCC guide as not requiring a shield, or perhaps the definition of a "shield".

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    \$\begingroup\$ I'm not sure if I understand your response. AFAIK, if the device is modular, a metal can / shield is required. Yet, some devices still use a shield inside whilst some don't. So I wonder why some still use a shield when regulatory bodies like the FCC have no such requirement. \$\endgroup\$ – Kar Jan 18 '16 at 16:18
  • \$\begingroup\$ If a device doesn't comply with FCC emissions rules, a manufacturer could try using a shield to bring the device into compliance. See EDIT on my answer for shielding out interference noise. \$\endgroup\$ – Marla Jan 18 '16 at 16:22
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    \$\begingroup\$ RF shielding is required for modular approval by the FCC. This is mostly done using a metal shield, although I've heard that some pass with sufficient ground plane shielding. "This is intended to ensure that the module does not have to rely upon the shielding provided by the device into which it is installed in order for all modular transmitter emissions to comply with Part 15 limits. It is also intended to prevent coupling between the RF circuitry of the module and any wires or circuits in the device into which the module is installed. Such coupling may result in non-compliant operation." \$\endgroup\$ – DigitalNinja Jan 18 '16 at 23:17
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    \$\begingroup\$ "I can now see where the original OP, and the commentor DigitalNinja have concluded a shield is necessary, even though I read the FCC guide as not requiring a shield, or perhaps the definition of a "shield"." It depends on the type of modular approval you want. If you know the host then you can get a "limited modular" approval without requiring a shield, but if you don't know where the module will be installed then RF shielding is required (i.e. it must meet all 8 requirements). This is why you see all OTS Bluetooth modules with a shield (they could be attached to all kinds of unknown hosts). \$\endgroup\$ – DigitalNinja Jan 19 '16 at 0:31
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    \$\begingroup\$ Also, as you stated "perhaps the definition of a "shield"" - it doesn't explicitly say "metal" shield, that's why I said a ground plane is sometimes sufficient, although for a single-modular transmitter (i.e. a standalone module) a metal shield is the easiest RF shielding mechanism, which is why you see them on a lot of OTS modules (whether it's wifi, BLE, etc.). My company just went through this with the FCC, that's why I can say these things with certainty. \$\endgroup\$ – DigitalNinja Jan 19 '16 at 0:34
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If a module is to be used for internal consumption a shield is not required as the product that your module is put down on will need to be tested. Any Module that is sold as a stand alone item must be shielded to get FCC approval. That is why you see a shield on brand name, certified modules. I would be very wary of any that claimed to be FCC and other agency approved that did not have a shield.

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The FCC defines a module for the purpose of pre-certification. So a company can sell you a module that is already FCC certified and that saves you the costs and time of having to certify your own product. You still have to certify the rest of the product but the wireless portion is taken care of. And there are strict rules on how the module can be used on the system and if you violate that you would have to still certify the whole thing.

As Marla said, 1) a shield would be added if the product can't pass EMI testing without it 2) a shield would be added to increase immunity from external EMI.

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