Can I perform any transmission regardless of my license as long as I'm inside an RF sealed enclosure, such that no RF will be detectable from my transmissions off my property?
I imagine the answer is yes, but I'd like to be sure I understand.
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asked Dec 12, 2013 at 16:21
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2$\begingroup$ If a microwave oven transmits 1,100 Watts inside a faraday cage, is it transmitting? $\endgroup$– SDsolarCommented Sep 12, 2017 at 19:32
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$\begingroup$ If you have a shielded room with both a transmitter and receiver in it, are you transmitting? (It depends on where your monitoring point is located.) Do people need licenses to operate microwave ovens? $\endgroup$– SDsolarCommented Sep 12, 2017 at 19:33
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1$\begingroup$ Microwave ovens are moot because they use the ISM band that was created for them. $\endgroup$– user10489Commented Sep 15, 2019 at 20:47
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$\begingroup$ @user10489 And they must because they leak enough to cause "harmful interference" in some cases. Else why all the warnings to pacemaker users about operating microwave ovens, and why not install them in airliners? $\endgroup$– Zeiss IkonCommented Sep 16, 2019 at 11:08
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7 Answers
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I don't have an answer actually clearly applicable to this situation, but a couple of related scenarios come to mind:
Every shielded digital electronic device is radiating "inside a RF sealed enclosure". Your scenario is different in that it's not a discrete device with built-in shielding.
Part 15 §15.211 permits tunnel radio systems to “operate on any frequency” provided that the emissions meet usual limits as measured at the tunnel mouth. However, this specifically applies to “a tunnel, mine or other structure that provides attenuation to the radiated signal due to the presence of naturally surrounding earth and/or water”, and not artificial shielding.
These are two cases where analogous things are occurring; neither one applies specifically here but they're both precedents which match the common sense “if no one else can receive it, it's OK”. This does not mean that it's actually legal.
answered Dec 12, 2013 at 18:16
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$\begingroup$ I wonder if there's any precedent to take the entire "transmitter + test enclosure" as a whole and call it the device — i.e. then wouldn't it simply fall under Part 15 as simply an unintentional radiator? $\endgroup$ Commented Jun 4, 2016 at 15:24
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This is pretty much the same as transmitting into a dummy load (or using the stock rubber duck antennas :) ).
I don't think a canonical answer is possible; Part 97 is silent on the issue. But, if no one can hear you, you can't be interfering with anyone or "using" the spectrum, so I would say sure. Depending on what you are planning on doing (and on which bands), you might want to make some RF checks at the edge of your property to be sure you aren't leaking RF.
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2$\begingroup$ Upvote for this one. You hit the nail on the head. Think of your microwave oven. Is it transmitting? $\endgroup$– SDsolarCommented Sep 12, 2017 at 19:31
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2$\begingroup$ It is: that's why microwave ovens operate on an ISM band where that transmitting is explicitly allowed. $\endgroup$ Commented Oct 3, 2019 at 15:41
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I'm trying to find a better source, but according to this letter from Boeing petitioning the FCC in 2011, an experimental license is technically required to operate even within a Faraday cage, although they have an unofficial policy of permitting such actions.
Finally, the Commission should codify its policy of permitting entities to conduct experiments within RF enclosures, such as anechoic chambers or Faraday cages, without an experimental license.
This makes sense as someone would have to complain before the FCC was involved. And such a chamber should be able to reduce the RF power going out to almost nothing, making the odds that someone complains very miniscule. Still, it could happen. If you use low power in such a device, you probably will be fine.
answered Mar 25, 2015 at 12:53
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2$\begingroup$ Actually, I interpret that quote to mean that they do not require an experimental license to operate in an RF enclosure, but that the policy is simply not on the books anywhere. $\endgroup$– glibdudCommented Apr 7, 2015 at 18:27
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1$\begingroup$ Good note, I've improved my answer based on that. $\endgroup$ Commented Apr 7, 2015 at 18:35
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The practical answer is yes, as long as (as others have nicely answered here) your signal cannot be detected outside the cage.
However, you might damage your transmitter. As an example, let's say you have a Faraday cage that's not much larger than your antenna. It might be impossible to tune the vswr for a good match, thereby heating the RF output stage beyond safe limits.
answered Sep 16, 2019 at 16:24
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Legalities aside, what I would see as a significant caution in this case is that unless you have constant monitoring and an automatic shutdown in place, you have no immediate way to be sure your Faraday cage hasn't failed. If your enclosure is damaged and you transmit, your transmission will propagate according to frequency and conditions -- and may cause "harmful interference" without you even being aware you're violating the law. Note that you are also bound by requirements to perform an RF exposure evaluation to ensure that your experiments are safe.
The microwave oven mentioned in comments is a bad example, because if (say) a door seal or the mesh in the window is damaged, it may leak enough microwave RF to cause significant problems without the operator being aware of it -- and even when in good condition, certain sensitive devices (older pacemakers, for instance) may receive harmful interference from the leakage.
Further, I would question what can be learned by transmitting at significant power inside a reasonably sized shielding enclosure -- reflections from the enclosure itself will swamp anything you might be studying as far as propagation, and will tend to amplify spurious emissions like harmonics (you'll detect the harmonic and its reflection from each wall of the cage, out of phase by some number of nanoseconds).
answered Sep 16, 2019 at 11:16
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1$\begingroup$ The asker probably really wanted an RF anechoic chamber rather than a "faraday cage" as such, the difference being that the anechoic chamber is made to absorb as much RF as possible, to permit useful measurements, rather than merely reflect it. $\endgroup$ Commented Sep 16, 2019 at 18:15
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$\begingroup$ @Zeiss, you haven't answered the question. The question assumes that the Faraday cage doesn't let any RF out.The answer is simple, yes or no. $\endgroup$– AndrewCommented Sep 16, 2019 at 23:41
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$\begingroup$ @Andrew Saying you may radiate without knowing it isn't the same as "no, it's (potentially) not legal"? Do I need to explicitly label it as a frame challenge? $\endgroup$ Commented Sep 17, 2019 at 11:01
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The answer to this question is really simple.
No.
You cannot legally transmit using radio equipment that you are not licensed to operate.
In fact in some cases you are not even allowed to own equipment that you are not licensed to operate.
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NO where I live the house heating is electric in the ceiling acting as a faraday cage no cell service in center of area and barely any on perimeter of building 2mtr and 70 cm same no service on HF lower freqs but marginal
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1$\begingroup$ Hi KB9JJJ, welcome to SE Amateur Radio Beta. Your post doesn't seem to be an answer to the question and is very unclear. $\endgroup$ Commented Sep 15, 2019 at 13:25