Part 15 of FCC rules - why the 2nd rule of interference?

Many have seen this text on electronic devices:

“This device complies with part 15 of FCC Rules.

  1. This device may not cause harmful interference.

  2. This device must accept any interference received, including interference that may cause undesired operation.”

[sub]3) You see Opal, the FCC does make a list of two items!![/sub] :slight_smile:

I understand the logic on the first rule but the second? What is the logic on that?

If for example you have a radio that is your only way to get info in an emergency, would it not be better to have one that is less prone to interference?

Hi Gigo.

FCC Part 15 is for unlicensed devices. If you have a unit that you need a license for, such as a ham radio or a land mobile radio you will not see the Part 15 warning.

All this is telling you is that you have no rights on the frequency. If someone comes along with another Part 15 device you can’t sue him for causing inteference.

See the Part 15 description at the FCC Website.

But, it is not proper to make a device impervious to interference if it is not a radio?

I see now that radio was a bad example, lets see: the rule I quoted is printed in a graphic computer tablet! Yes it is not licensed, but this is not radio: it has a direct connection to the computer. It is, if I get this correctly, open to interference from other sources; why?. I am still confused.

And this is even after I see your point; yes, one has no right for the frequency, but if is there a problem if someone sells a device that prevents those frequencies from getting into it?

Do you mean if someone sold device ‘A’ that prevented RFI from intering your device ‘B’?

There is no problem with that. In fact, if someone came up with a catch-all device that could do it, amateur radio operators the world over would swear that a god existed.

They constantly battle RFI in their neighbours homes, (not that they have to) in order to keep the peace.

Many electronic gadgets can be affected by radio transmissions. My home alarm was going off apparently for no reason until I found out by chance that it happened every time a guy with a ham radio rig in his car drove down the street. His transmissions interfered with pretty much everything in the house. I had to turn the computer speakers off too because they make a very loud noise. It is possible, although less likely, that a computer device could malfunction. What they are telling you is that you cannot complain about this. And the reason these devices are not made impervious to all radio waves, as well as wind and tide, is because it is cheaper and unnecessary most of the time.

Okay, I can understand why you can’t complain about interference, but I still see GIGObuster’s point. Why is it against FCC rules for a device to block that interference?

IWhere does it say the device cannot block the interference? It just says it has to “accept” it, meaning you cannot complain to the source of the interference. You can build a keyboard which is specially designed to withstand such interference and nobody will say anything.

The FCC thinks in terms of legal priorities and international treaties for keeping RF neighbors playing nice, and especially protecting public safety and emergency services. As such, it classifies devices within a regulatory plan. A device may have traits covered by that plan, and others not so. One cannot presume anything about a device’s unregulated characteristics from regulatory limits on other narrow criteria.

Part 15 sets limits for intentional radiators, and unintentional radiators. That would include baby monitors, garage door openers, RF alarm sensors, and Wifi networks as intentional. Most receivers, digital devices, etc. that aren’t intended to transmit but incidentally can are unintentional radiators. In general intentional radiators are restricted to bands of frequencies that may cause problems to similar devices, but not to protected services on other frequencies. Unintentional radiators are presumed to potentially cause problems from 9 KHZ to light, and be restricted to signal leakage levels less likely to do so.

Nearly anything can act as an antenna, including a grounded case, to receive or transmit.

Under the wrong circumstances, there can be conflicts between devices with combinations of signals that normally wouldn’t cause serious problems. Under extreme conditions (eg, making a PC and phones work at a high power transmitter site), it can take serious work to get non-RF devices, never mind receivers, to work properly or at all. Enough RF can rectify and power lights with no AC connection, never mind do odd things to semiconductors.

If a non-priority device of any kind (including licensed transmitters) causes harmful interference (as legally defined), the FCC can generally order it shut down. That’s at times included cable premium channels leaking from defective coax near aviation frequencies. It includes some light bulbs. (Yes, the FCC can come into your home or business and order you to turn off and replace lights.) That includes 250 watt paging transmitters interacting with 50 KW broadcast transmitters, if they’re harming aviation.

Part 15 devices are at the bottom of the pecking order. They’re often cheap items, though not necessarily. They can be $6000 industrial test gear or $100,000 instruments. They can be 37 cent production cost toys. They can be the receiver section of a transceiver, the other half of which is licensed. You’re free to buy whatever quality you prefer or need, but if what you buy doesn’t meet your needs relative to protected causes of RF interference, a Part 15 device has no “rights” (claim for legal protections against other devices or their users), while other devices may or may not have “rights” against Part 15 devices. The $6,000 Part 15 device is just as unprotected as the 37 cent one.

Usually cost is what drives lower quality and more susceptibility to malfunction under adverse conditions, such that consumers pay for just what they get. No matter the cost, there’s no such thing as an impervious design. In the case of a protected service being harmed, the Part 15 device always loses. In the case of various Part 15 devices, everyone loses if users don’t negotiate resolutions, though it’s their problem and not one where anyone has a legal claim.

Again, you’re free to buy whatever quality you prefer and can afford. Part 15 isn’t about that, but defining standards for what can be made to transmit in unlicensed use, and background noise levels that determine when devices are harmful, without which assault lawyers could duke it out for those who could afford to pay.

Part 15 would limit what neighbors with crappier electronics than yours could do to harm your ability to receive emergency signals (mostly by manufacturer controlled limits the user doesn’t change). It doesn’t say how good your electronics need to be otherwise. That’s your problem.

Ah, I guess I was misunderstanding it. That’s what I get for not being a techie. Thanks! :slight_smile:

Light entertainment: I was waiting for a friend near a Wal-Mart, in the late 1990s, and as he drove in, everything shut down and locked up. He’s got a ham radio in his car, and they use wireless technology for the registers. And yes, they have to ‘accept’ that.
They may be more secure now, but until recently, you could steal credit card numbers with a wireless PDA, from the leakage.

Anyone here have any military comm spec friends? Want to make them give painfully twisted funny faces?

Learn about Tempest, E-cubed, and similar programs, and start talking about details they don’t know that touch on what little pieces they do. E^3 refers to “hardening” electronics against a nuclear electromagnetic blast. Tempest refers to a mix of hardening electronics to resist such blasts and other intentional countermeasures of an enemy, as well as reducing leakage so as to be less detectable as to one’s presence or the unsecured content of communications.

Most military electronics secrecy issues are more traditional though. Train the sloppy, negligent, and often sleep deprived humans to never do anything foolish.