I am looking at creating a device within regulations for a medical environment with two Txing antennas, BLE (cypress FCC certified module) and 915MHz ST Spirit1 FCC certified module.

I have found multiple sources on the usage of the 915MHz band and other ISM bands. But I believe there is/are regulation(s) about the distance required between these two ‘co-located’ antennas, ie 915&2.4GHz in this case, but I cannot find the specific regulation. Has anyone had any experience with this or able to point me in the right direction?

Any help would be greatly appreciated!

Edit ****

Think what I may be after is ‘Section 15.212, Modules, Module Certification’

This is to do with modules, which will probably be used but a custom PCB config. maybe be used.


2 Answers 2


Modules are typically certified with the assumption that they are the only intentionally radiating device. Some module datasheets will make this known with statements like:

This transmitter must not be co-located or operating in conjunction with any other antenna or transmitter.

Note, it says with any other antenna or transmitter. So, even if you figured out a way to share the same antenna, there would still be an issue.

I'm not an expert on the regulation side but I'm assuming it's not even possible to certify a module in a multi-transmitter configuration without knowing the entire configuration ahead of time.

It's important to talk to the module manufacturer, test houses and maybe even a consultant/lawyer that is an expert in this particular area so that you're not violating any FCC rules/regulations.

UPDATE: I've personally been working with TI on a similar situation and they will provide (through application) a letter that will allow us to use their data on our own FCC ID. There is still additional testing required due to multiple transmitters but the effort/cost is going to be much lower than trying to certify from scratch. Another option is request the manufacturer to file for a Class II Permissive Change on their FCC ID to allow your multi-transmitter configuration. However, I've yet to come across a manufacturer that is willing to do this.

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    \$\begingroup\$ In addition to datasheets, this sentence is often found in the FCC grant issued for modules: example for Laird BTM4x1. \$\endgroup\$
    – dim
    Sep 27, 2018 at 11:53

I doubt such a regulation exists, after all it is fully permissible to share the same antenna among multiple radios, provided the full assembly meets the regulations.

How near you can place the antennas is defined mostly by the quality of the analog input filter on your receive circuitry, as you will need to block the other transmission from overloading the input amplifier. So, it's a technical, not a regulatory problem.

Since you are going with pre-certified modules, the module vendors would be the people to ask here.

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    \$\begingroup\$ I believe the FCC rules do not allow devices with multiple transmitters (even with module approval) to be sold without certification testing. This rule appears to be frequently broken but if you are operating in a medical environment the potential liability associated with not being in compliance of FCC rules is probably unacceptable. \$\endgroup\$ Feb 12, 2018 at 15:53
  • \$\begingroup\$ @DeanFranks, yes, my answer is rather specific to the question (whether there is a requirement on antenna distance), that's why I also mentioned testing the full assembly. \$\endgroup\$ Feb 12, 2018 at 16:04
  • \$\begingroup\$ Understood, I was just clarifying since @ConfusedCheese said "within regulations" and seemed to be assuming that the module level certifications would still be valid with multiple intentional radiators in the same device. \$\endgroup\$ Feb 12, 2018 at 16:59
  • \$\begingroup\$ Hi guys, thanks for the input. I think Dean is onto what I fear is the problem but am struggling to find the literature. Have you any experience with this? I feel i’m missing a legal term to describe it to catch it. I thought it might be ‘collocation’ of antennas, but this only appears to be for masts or large objects. \$\endgroup\$ Feb 12, 2018 at 23:26

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