5 ms·

What I don't get it is, why make the software enforce certain frequencies? If the hardware should never be able to broadcast on a certain frequency, why not bui

by jordigh 11y ago

What I don't get it is, why make the software enforce certain frequencies? If the hardware should never be able to broadcast on a certain frequency, why not build the hardware with that limitation?

gress 11y ago
Perhaps because that's more costly? Sometimes the disallowed frequencies exist within a range of allowed frequencies. A hardware limitation would involve filter stages that would add cost.
- lexicalscope 11y ago
  This is already done in scanners to prevent scanning cellular frequencies as required by FCC regs.
CamperBob2 11y ago
You can't. RF hardware and signal processing don't work that way... at least not for free.
- lexicalscope 11y ago
  You can make it difficult and very hard in practice through antenna and component design in the case of small internal radios - in radios with external antennas it becomes a great deal harder though, and in radios that are open for modifications it becomes even more difficult. That being said though - this is meant to apply to software defined/modular radios - that is systems wherein the entire point is that it does what the software tells it instead of having hardwired components meant only to receive certain frequencies.
rcthompson 11y ago
In addition to the other answers, allowed frequencies differ in different countries/jurisdictions, so it's probably cheapest to make a single piece of hardware that can handle all frequencies in all jurisdictions, and then impose region-specific restrictions in software.
lexicalscope 11y ago
This is because this is entirely intended for software defined radio and modular radio - around which the entire point is the RF component does not contain as much signal processing logic, and that is done in software. Restricting software defined radios to specific frequencies in hardware would take away the entire point of modular/software defined radio.
- PhasmaFelis 11y ago
  Did you miss the conversation about how this fucks over people who want to install custom firmware on their routers for legitimate administration and traffic-shaping? There are plenty of uses for radio software that don't involve going outside approved frequencies.
  - lexicalscope 11y ago
    I agree - but this rules doesn't apply to anything except SDR and modular systems that are also consumer devices - which are not most consumer devices. That said - I am not condoning the FCC policy at all - I'm actually against it - I just don't really care that much because it impacts nothing I do and so few use cases I care about.
    - PhasmaFelis 11y ago
      Does it affect cellphones? From the description I would have assumed it did, but I haven't seen much talk about that.
      - McGlockenshire 11y ago
        Even if it does apply, the radios on modern phones are already black boxes and completely detached from the rest of the phone. Some consider them a significant security threat already.
    - fnordfnordfnord 11y ago
      >"I don't care about X, because I never X." You sure have spent a lot of time ITT explaining to everyone, advocating, practically that the FCC ruling is unimportant because you think that your own interests will be unaffected. Well, congratulations, but if we were all so short-sighted we'd eventually be reduced to only the hobbies and activities that a majority of us approve. We get it. You don't care, because you don't think it affects you.
paulmd 11y ago
In the past that's exactly what they've tried to do, and this usually ends up clobbering the law-abiding users in the process. Most of these bands are pretty close to each other - the 10M HF band is right next to the CB band, the 2M band is right next to the emergency services bands and pretty close to both the aviation bands and the weather radio bands, and so on. Gear from one will pretty much just work on the nearby bands, absent some other protection. You can do filtering, but it's physically pretty hard to make an amplifier work ideally within its band and then immediately stop working when you take it outside its band. So the FCC's response in the past was to make it illegal to produce anything that could go from [unlicensed power level] up to [licensed power level] on demand. If you wanted to make a 10M amp that could hit say 150W, you had to require at least 75W drive power because that was beyond what a legal CB radio could deliver. Kinda sucked for anyone who couldn't afford a radio with 100W of drive, and I think they eventually let off a bit because they were losing the battle to cheap Chinese junk sold over the internet. They're very proactive about enforcement, they'll get you sooner or later, but until then it's better for everyone if you're not spewing harmonics everywhere. There are radios and amps that use a frequency analyzer to automatically cut out when operated out of their intended bands, they're just very expensive compared to most of the gear that's out there. And a lot of the Software Defined Radios and so on are actually wideband radios that are physically capable of operating across a bunch of bands. These are very concerning for the FCC, and you pretty much cannot limit these physically, it has to be built into the firmware or the controlling software. Hence the article. There's also just different rules for different license classes. As a radio amateur, I can also use 2.4 GHz (13cm band) under my license, and I am allowed to operate with up to 1500 to 2500 watts EIRP depending on mode. That is of course subject to lots of limitations including "minimum necessary power", but there's nothing physically stopping you from taking a 13cm amp sold for radio amateurs and running wifi over it. Same frequency, how does the radio know?
- PhasmaFelis 11y ago
  > There are radios and amps that use a frequency analyzer to automatically cut out when operated out of their intended bands, they're just very expensive compared to most of the gear that's out there. Why is that expensive? It obviously can't require fancy hardware if it can also be done in software.
csirac2 11y ago
This goes beyond just frequency and power conformance. There's power negotiation, interference avoidance, instantaneous occupied bandwidth, instantaneous vs average power limits, spread spectrum/freq hopping performance, radar avoidance algorithms - it took a lot of effort to carve up the 5GHz bands, each part of the world has done it differently, and so there's a lot more strings attached.

by jordigh 11y ago

What I don't get it is, why make the software enforce certain frequencies? If the hardware should never be able to broadcast on a certain frequency, why not build the hardware with that limitation?

gress 11y ago

Perhaps because that's more costly? Sometimes the disallowed frequencies exist within a range of allowed frequencies. A hardware limitation would involve filter stages that would add cost.

lexicalscope 11y ago
This is already done in scanners to prevent scanning cellular frequencies as required by FCC regs.

CamperBob2 11y ago

You can't. RF hardware and signal processing don't work that way... at least not for free.

lexicalscope 11y ago
You can make it difficult and very hard in practice through antenna and component design in the case of small internal radios - in radios with external antennas it becomes a great deal harder though, and in radios that are open for modifications it becomes even more difficult. That being said though - this is meant to apply to software defined/modular radios - that is systems wherein the entire point is that it does what the software tells it instead of having hardwired components meant only to receive certain frequencies.

rcthompson 11y ago

In addition to the other answers, allowed frequencies differ in different countries/jurisdictions, so it's probably cheapest to make a single piece of hardware that can handle all frequencies in all jurisdictions, and then impose region-specific restrictions in software.

lexicalscope 11y ago

This is because this is entirely intended for software defined radio and modular radio - around which the entire point is the RF component does not contain as much signal processing logic, and that is done in software. Restricting software defined radios to specific frequencies in hardware would take away the entire point of modular/software defined radio.

PhasmaFelis 11y ago
Did you miss the conversation about how this fucks over people who want to install custom firmware on their routers for legitimate administration and traffic-shaping? There are plenty of uses for radio software that don't involve going outside approved frequencies.
- lexicalscope 11y ago
  I agree - but this rules doesn't apply to anything except SDR and modular systems that are also consumer devices - which are not most consumer devices. That said - I am not condoning the FCC policy at all - I'm actually against it - I just don't really care that much because it impacts nothing I do and so few use cases I care about.
  - PhasmaFelis 11y ago
    Does it affect cellphones? From the description I would have assumed it did, but I haven't seen much talk about that.
    - McGlockenshire 11y ago
      Even if it does apply, the radios on modern phones are already black boxes and completely detached from the rest of the phone. Some consider them a significant security threat already.
  - fnordfnordfnord 11y ago
    >"I don't care about X, because I never X." You sure have spent a lot of time ITT explaining to everyone, advocating, practically that the FCC ruling is unimportant because you think that your own interests will be unaffected. Well, congratulations, but if we were all so short-sighted we'd eventually be reduced to only the hobbies and activities that a majority of us approve. We get it. You don't care, because you don't think it affects you.

paulmd 11y ago

In the past that's exactly what they've tried to do, and this usually ends up clobbering the law-abiding users in the process. Most of these bands are pretty close to each other - the 10M HF band is right next to the CB band, the 2M band is right next to the emergency services bands and pretty close to both the aviation bands and the weather radio bands, and so on. Gear from one will pretty much just work on the nearby bands, absent some other protection. You can do filtering, but it's physically pretty hard to make an amplifier work ideally within its band and then immediately stop working when you take it outside its band. So the FCC's response in the past was to make it illegal to produce anything that could go from [unlicensed power level] up to [licensed power level] on demand. If you wanted to make a 10M amp that could hit say 150W, you had to require at least 75W drive power because that was beyond what a legal CB radio could deliver. Kinda sucked for anyone who couldn't afford a radio with 100W of drive, and I think they eventually let off a bit because they were losing the battle to cheap Chinese junk sold over the internet. They're very proactive about enforcement, they'll get you sooner or later, but until then it's better for everyone if you're not spewing harmonics everywhere. There are radios and amps that use a frequency analyzer to automatically cut out when operated out of their intended bands, they're just very expensive compared to most of the gear that's out there. And a lot of the Software Defined Radios and so on are actually wideband radios that are physically capable of operating across a bunch of bands. These are very concerning for the FCC, and you pretty much cannot limit these physically, it has to be built into the firmware or the controlling software. Hence the article. There's also just different rules for different license classes. As a radio amateur, I can also use 2.4 GHz (13cm band) under my license, and I am allowed to operate with up to 1500 to 2500 watts EIRP depending on mode. That is of course subject to lots of limitations including "minimum necessary power", but there's nothing physically stopping you from taking a 13cm amp sold for radio amateurs and running wifi over it. Same frequency, how does the radio know?

PhasmaFelis 11y ago
> There are radios and amps that use a frequency analyzer to automatically cut out when operated out of their intended bands, they're just very expensive compared to most of the gear that's out there. Why is that expensive? It obviously can't require fancy hardware if it can also be done in software.

csirac2 11y ago

This goes beyond just frequency and power conformance. There's power negotiation, interference avoidance, instantaneous occupied bandwidth, instantaneous vs average power limits, spread spectrum/freq hopping performance, radar avoidance algorithms - it took a lot of effort to carve up the 5GHz bands, each part of the world has done it differently, and so there's a lot more strings attached.