Over the last few weeks a discussion has flourished over the FCC’s Notification of Proposed Rule Making (NPRM) on modular transmitters and electronic labels for wireless devices. Some folks have felt that the phrasing has been too Chicken-Little-like and that the FCC’s proposal doesn’t affect the ability to install free, libre or open source operating system. The FCC in fact says their proposal has no effect on open source operating systems or open source in general. The FCC is undoubtedly wrong.
Be sure to actually read the article.
One of the arguments made in the article is: what if your one watt (the legal max) wireless router suddenly began transmitting at 1000 watts? Okay. I don’t think that can happen without modding the router. I don’t believe that manufacturers leave any money on the table when designing electronics. Can third party firmware push the power output past its design limits without distorting the signal beyond usability? I’d like to know how and if this would be possible. Any ideas on this?
Usually to transmit above the power limit a significant amount you’d have to be using a non stock antenna… in which case you could easily break the law. It’s not worth the loss of freedom though IMO.
Wifi routers don’t usually have a PA stage.
They usually have a driver FET straight to the output.
You could drive it at 2-3 watts maybe, and overbias/drive the f–k out it, making it seriously non-linear to maybe 5 watts.
5 watts in an ISM band isn’t going to be dangerous for anyone.
However … if you overdrive/bias the thing, it will become seriously non-linear.
In short, this means you risk knocking your neighbor’s wifi off the air.
I dno where the 1000 watt claim comes from, but it is simply ridiculous.
High power microwave radios are very expensive.
Realistically, getting an AP to output 10w or more of mean power would be pretty expensive, and it would mean using an external amplifier.
1 KW would be prohibitively expensive (AND DANGEROUS!).
Here is a 10w 13cm pa for amateur radio use: http://shop.kuhne-electronic.de/kuhne/en/shop/amateur/leistungsvers…
It costs 320 euros.
Granted, the design is totally different, and that PA probably doesn’t have enough bandwidth in the bandpass to do wifi, but you get the idea …
Building a 1 KW solid state wifi-capable PA would be pretty expensive.
ISM bands are being used and abused by a lot of people for a lot of things.
Motion sensors, cordless phones, bluetooth, car key fobs, GMRS/MRS, PMR, you name it …
With the exception of UHF (like GMRS,MRS,PMR and some key fobs), you really don’t risk disturbing anything important if your radio freaks out.
On 5 ghz, you could POTENTIALLY cause a problem for radar stations on a non DFS frequency … potentially …
Anyway, TL;DR vvv
It’s good that there are laws concerning band preservation and such, HOWEVER … wifi aps and such are cheap. The radios operate at design capacity. You can’t really extract that much more power out of them without seriously degrading the signal.
If you do, the only thing you risk doing is interference with adjacent channels and really … your own devices. The modulation will probably be pretty horrible, and your own devices will have a hard time with it. Lots of retransmits, etc.
EDIT:
Another big issue the article forgot to touch on.
It’s such a simple concept, really.
Let’s say you do invest in a 1KW wifi PA …
Your devices will hear it over large distances alright, but who cares … it’s not like your laptop will be putting out 1KW to get back to it …
Oh well …
Edited 2015-09-22 06:41 UTC
The 1kW example was just an exaggeration to make a point. IF someone had a router capable of 1kW, they could interfere with a LOT of other wifi users in the area without meaning to. You can see that easily with 1kW whereas you wouldn’t with 2W. So 1kW is more understandable as an example of what he meant than 2W.
And if you think “that’s silly, no one would even make a wifi router that had that power,” just look at this:
https://www.yahoo.com/tech/s/anonymizing-wi-fi-device-2-5-mile-range…
I doubt it was 1kW, but it was certainly much more than a couple watts.
I sincerely doubt the 2.5 mile claim.
As i said, you can put out all the power you want, it’s useless if the device you’re reaching can’t get back to you.
The antennae on that look like standard lossy rubber duck antennae on SMA connectors.
If you want to be able to reach a device far away, and make sure you hear it come back to you, the only way to do this correctly is by using the correct antenna.
Yagis, patches, sectors, dishes, etc.
Omnis are the worst way to cover a distance.
Agree.
From what I read on somewhere place, the real problem is that the RF circuitry components are a bit generic, what helps keep costs down, and as so can be abused, i.e., can be programmed to operate on a RF spectrum outside of the original FCC approval for it.
I guess it would also imply a less than optimal situation for the antenna and more spurious RF signals being broadcast and, as so, more chance to interference.
If FCC obligate them to use components with more stringent parameters of operation the cost will certainly rises (or so I think).
Anyway, I really hope common sense will prevail on the end as I don’t know too many companies that keep patching their middle to lower cost products to fix security flaws for a reasonably time span and the community projects (like dd-wrt and openwrt) have been very helpful to cover this particular deficiency. Even more when we take in account that the community projects extend the functionality of the devices.
A modem or other wireless computer device could be modified to operate illegally via hardware mods and changes to the firmware in the devices, but by operating system drivers? I’m not so sure. I’d like to learn more if anyone has an easy-reading (non technical) link.
A good example (on the receiving end) is the use of DVB-T TV stick for SDR radio.
Check out http://www.rtl-sdr.com and make your own SDR receiver for 10 bucks or less.
Nice link, thank you.
Yes, thank you.
Anyone could buy the parts to build an illegal broadcast station, signal booster, or jammer. Basic stuff.
But that’s not quite the fear hinted at by the article in which the author believes the FCC could clamp down on Linux and other non-OEM drivers because they might be used to alter or strengthen the broadcast signals of common consumer devices such as modems.
I’m still wondering, by modifying only the drivers found in an operating system, is it possible to alter the broadcast strength or frequency of a wi-fi or bluetooth device?
OK, found from where I read:
http://www.infoq.com/news/2015/07/FCC-Blocks-Open-Source
https://news.ycombinator.com/item?id=9959088
Look specially for power and channel selection.
It is possible to use channels that aren’t allowed in your area, and boost the power output if the radio supports it.
No, the 2.5 mile claim is easy to believe. Walkie-talkies and CB radios have the same kind of antenna, and easily reach further with low powers. The kind of antenna you’re talking about is for trying to pick up signals dozens of miles away, not a couple.
These are analog devices and as so are way more forgivable to noise/distortions (we are the processing units responsible to make sense of whichever is received, amplified and generated).
On routers and other receivers/transmitters the requirement is much more stringent, specially more as they are made to operate on conditions where interference, noise and distortion are very likely to be present and they are responsible to make sense of the RF signals they receive. It is really a different set of constraints.
Some walls or close networks is all what is needed to degrade the original signal to the point most of it is discarded.
Of course, you don’t need 1 KW but don’t expect ordinary routers to have a long range operation.
Edited 2015-09-22 18:32 UTC
Um … no.
CB radios are HF. 27 MHZ, +- 11 meters wavelength.
The walkie-talkies you are (probably) talking about are UHF, 440 MHZ, +- 70 cms wavelength.
Wifi is 2400 MHZ, +- 13 cm wavelength.
The antenna design differs a LOT based on the application.
The HF antenna you’ve seen will probably be a 5/8ths antenna with a ground plane. It is designed to radiate upwards on the vertical plane, forming a cone like projection. It has some lobes protruding outwards on the horizontal plane as well. Environment and such will influence the radiation pattern.
The antenna in a walkie talky is very different, as is the wifi antenna … they are designed to radiate outwards on the horizontal plane.
They also operate on different bands altogether. The wifi antenna’s loading will relate to a much smaller portion of the full wave than the walkie talkie.
Without getting too much into specifics of radio wave propagation and antenna design, i can tell you that VHF and up can only be used for line of sight communications (barring special atmospheric conditions). This is why radio towers have to be so high … to get a wide line of sight.
Do you think cell phone companies put up cell towers and make them so high just for fun?
An LTE cell phone tower, which has lots of powerful radios and directional antennae (those beams you see are sector antennae), which is near enough to wifi in the bands to be relevant has an operational range of 1 to 5-6 miles depending on surroundings, height, etc.
Sometimes it is LESS than a mile.
The device shown there MIGHT get a 2.5 mile operational radius if it is placed high enough on a tower, on an open field. And even then, doubtful. Note that there is a big difference in the detection of a signal (RSSI), and the clarity of a signal (SNR).
If you place said device inside of a building, surrounded by walls and 13 cm RF absorbing waterbags known as people, it will NOT have an effective operational radius of 2.5 miles …
Sorry, guy, but you’re wrong.
I do this for a living.
PS: That little humble CB can talk to people across the pond given the right atmospheric conditions.
Edited 2015-09-22 18:38 UTC
You can nay-say all you want and CLAIM you’re a professional, but I OWN walkie-talkies that have the same kind of antenna as on your average wifi and they work fine out to about 5 miles. I have a hand-held CB transceiver that looks like one of those old cordless phones that also has the same kind of antenna as wifi and it works out to 10 to 15 miles depending on the weather and where I’m using it.
Yes, special antennas will work better, but lots of electronics use that pathetic little antenna just fine in the range we’re discussing. Just walk through a store once or twice and look at all the stuff using this type of antenna. It’s downright ubiquitous for cheap, low-end devices.
You OWN walkie talkies and a CB, do you? WOW! SWEET!
Just because it looks like the same antenna doesn’t mean it is the same antenna. They will certainly not perform on the same level …
Your cb works with an 11 meter wavelength.
Your walkie talkie works with a 70 cm wavelength.
Your router works with a 13 cm wavelength.
In order for the antenna to radiate properly and efficiently, it needs to be resonant on the frequency you are transmitting on. There are exceptions to this, but as a general rule, this holds true.
If the antenna is non-resonant, the excess energy will be sent back down the transmission line into your equipment. The ratio between forward and returned power is called SWR, or Standing Wave Ratio.
If you use a mismatched antenna on a transmitter designed for a different antenna, you will cause a high SWR situation. Most of the energy will be sent back into the transmitter, where it will dissipate as heat in the final stage of the transmitter. On low power applications (such as wifi routers, your walkie, etc), it doesn’t matter.
Your CB might fry if you do this for too long. Or if you transmit without an antenna … which is bad.
There are other important factors such as impedance, which needs to be matched to your transmitter.
Now … allow me to explain …
Let’s take a very simple antenna as an example. The humble dipole. It is simple and omni-directional.
It’s used by many routers on the pcb in the form of a pcb antenna.
Ideally, the combined length of the elements needs to be the full wavelength.
So for your CB, that would be 11 meters.
For your walkie talking, it would be 70 cms.
For a wifi router, it would be 13 cms.
There are other factors that can alter the length such as the velocity factor of your coax, any loading that is used, etc, but GENERALLY, this is true.
Now …
It is impractical to put an 11M dipole antenna on a cb radio, or a 70 cm dipole on a walkie talkie.
So … we need ways of shortening the antenna.
You can fraction the wavelength. Simply dividing it in two for example. For a dipole, this would give us a half-wave dipole. That would still leave your CB with a 5.5 meter dipole and your walkie talkie with a 35cm antenna. The router on the other hand is now a much more manageable 6.5cm …
Now …
Those little rubber duck antennae that you see on everything from walkies to wifi routers are loaded fractional vertical antennae.
They are nothing but a little copper wire with some coils wound in them.
You can shorten an antenna significantly using inductors (coils), and capacitors.
Do note that the energy that goes into the coil is essentially wasted.
Their designs vary from very simple to somewhat complex.
A multi-band portable handset (or walkie talkie) will have a complex antenna.
Let’s say it needs to be able to transmit on VHF and UHF for example. This is very common. That would mean that your antenna needs to be resonant on 2 meters and 70 centimeters wavelengths. These are usually a stacked design (multiple antennae on the same transmission line / wire). The design gets more complex quite quickly as the requirements go up.
For your walkie, just as for a router with en external rubber duck antenna, it will be a length of copper wire in a plastic tube with a coil wound in it to load it so that it can be short and still be resonant.
The wifi antenna will be similar, but with much less loading since the wavelength is shorter, and thus the wire comprises a larger fraction of the wavelength.
Now for dual band APs with external antennae, things are more complicated yet again …
Anyway …
A picture is worth a thousand words:
Wifi antenna: http://cdn.instructables.com/FNO/98RT/GOW48ZAT/FNO98RTGOW48ZAT.MEDI…
Dual band GSM antenna (notice the TWO coils): http://g02.a.alicdn.com/kf/HTB1Pg4zIXXXXXa1XVXXq6xXFXXXW/20pcs-GSM-…
PMR or GMRS or MRS radio (not sure): http://www.jpole-antenna.com/wp-content/uploads/2015/08/Uhf_cb_wit_…
Now … as for your claims …
There are people that can talk across the english channel with a 0.5 watt UHF PMR radio. Why? Line of sight and salt water.
What is the practical range of such a radio in an urban environment? 1-2 km at most.
If you have a free line of sight in a large open space, you can get very far with very little power.
Now … on to wifi / microwaves.
Microwaves are absorbed in water. This is how your microwave oven works …
Higher energies / higher frequencies are more easily absorbed in the surroundings. This is why wifi doesn’t get very far in real-life situations.
Then there is the whole misconception that power = range.
It’s not.
For the same antenna and transmission line setup, doubling your power output will only increase your apparent signal strength (RSSI) by 3 db.
In most cases, this is something like 5-10% on your signal bar …
It differs with implementation.
Now …
Going from 1 to 2 watts is manageable, and you get a 3 db gain … fine.
Going from 2 to 4 watts is probably not doable on stock hardware. You get another 3 db gain … ok … remember, this is RSSI, not SNR.
Going from 4 to 8 watts is going to be pretty expensive, and that will net you 9 db of gain.
Now, if you put a high-gain antenna on your router, you can legally produce up to 6 dbi of gain with less than 10 bucks.
You can even make the antenna yourself.
12 db of gain is easily doable without doing anything special. It will still cost you only a few bucks.
Well, whatever, it’s not like i expect you to take the effort to read all of this.
Good luck with your walkie talkies and all.
I admit I truly enjoyed that post and read it twice. It brought back some good memories of physics classes years ago.
Thanks.
You’re awesome
If you want to ban nefarious use and abuse of the wireless signal, then ban nefarious use and abuse of the wireless signal. Don’t ban an unrelated act that may or may not (see almost always not) enable a person to nefariously use or abuse the wireless signal.
When I read the original proposal, a great deal of the “don’t do that” wording was geared towards “if you do, you need a new label and new certification”.
So to use real world examples, if I buy a router with Linksys’s firmware on it, and rewrite the firmware with DDWRT, then the FCC no longer considers it the same device, and it’s sticker (the one that says FCC approved) is invalid.
From a technical standpoint, I can’t really argue with this logic.
What I don’t know how to deal with, is how do you re-certify this device, allowing people to tinker, while at the same time, protecting the affected spectrum from abuse?
They’re in a tough area for a regulatory agency.
Nothing can stop you from placing an amplifier in the transmission line, regardless of the operating system/
This whole article is just FUD.