2.4GHz-Friendly Phones?

da3dAlus writes "When I first bought my 2.4GHz wireless phone system several years ago, it was a rather new technology, and wi-fi wasn't even on the scene. Now it appears that all wireless phones are on the 2.4 or 5.8 GHz spectrum, and I've got neighbors with wi-fi (with myself included). While checking out new phones recently, I've noticed some are carrying a "802.11 Friendly" sticker. The question is, are there any trully 802.11 friendly phones? Has anyone really ever had a problem with these types of phones interfering with their wi-fi network?"

Comments

Yes, I have

[Lordofohio]

We had to stop using our brand new 2.4Ghz phones at work because our wi-fi stuff wouldn't hold a signal when the phones were in use. Keep in mind this was 2 years ago, haven't tried anything since.

Vtech

[jcostantino]

We just bought a Vtech 2.4ghz phone system - two handsets, one base w/ answering machine and a base with a charger. The system said "2.4ghz Friendly" and it replaced a Vtech 2.4ghz phone bought earlier in the year (and subsequently killed during a storm) which would knock the 802.11 offline unless I set my AP to channel 6.

I haven't bothered to change the AP to a different channel but so far it's working fine.

Worthy of mention is that the new handsets come with speakerphone and use three NiMH AAA cells instead of a shrinkwrapped battery with a lead. Plus they sound great and I don't have the problem I used to have on the older phone where the microphone was too sensitive and I heard background noise at too high a level in the earpiece.

2.4 GHz phones == bad idea

[Anonymous Coward]

I've gone back to the older 900 MHz phones since installing a WiFi network at home. The WLAN didn't interfere with the 2.4 GHz cordless phones we had, but the phones knock the network down hard. I haven't heard anything about "802.11 friendly" labels on newer 2.4 GHz phones, but I'd be skeptical. If they work at all, they work by adaptively locating an empty part of the 2.4 GHz spectrum, and around many crowded residental areas, there ain't no such thing no mo'.

You can also get 5 GHz phones, too. Either 900 MHz or 5 GHz is fine, just keep 'em off 2.4 GHz.

WiFi and 2.4GHz Don't Mix

[pbwiz]

WiFi (802.11b) and 2.4GHz Phones almost always will clash -- but there is a good article on wifi planet that gives some things that can be done to lessen interference.
http://www.wi-fiplanet.com/tutorials/article.php/2 191241/
Of course, the best solution is a 900MHz or 5.8GHz Cordless Phone.

Re:My microwave

[John Miles]

Household microwave ovens spew a lot of 2.4 GHz energy all over the band (enough that after looking at it on a spectrum analyzer, I no longer feel like pressing my face up to the window to see if the cheese on my pizza has melted yet).

However, they radiate only on alterating half-cycles of the 60 Hz line frequency. There may be a config option in your WLAN hardware's client utility to make it more resistant to microwave-oven leakage by forcing transmission of smaller packets. You'll lose some performance if you enable it, but it should keep your WLAN from going down altogether.

Re:5.8

[Glonoinha]

You mean like the 802.11a wireless networks?

But the first guy hit it right on the head. 900MHz phones are the best bet if you are running a regular wifi network and don't want interference.

Re:Why YES, I have had problems

[prockcore]

So, I had a linksys wifi router and an AT&T 2.4 gHz phone... They fought like dogs!

I'm willing to bet that the linksys you've got is the first generation BEFW11S4. I had problems with my 2.4ghz phones but when I upgraded to linksys's 802.11g router, all my problems went away.

I'd recommend upgrading because if a 2.4ghz phone causes your router to die, then its likely that your router won't play well with others. If your neighbors get 802.11b/g, your router will die a horrible death.

Re:I get interference

[Cyberop5]

I've tried a few 5.8ghz phones. They have horrible range and still pollute 802.11a. The quality is better, but not being able to leave the room with the base antenna doesn't really help.

Just stick to 900mhz for the best range and wireless reliability.

Re:No problems in my house

[jwcorder]

Not to nig your post here, but there is no way he cracked YOUR WAP with NetStumbler unless he just left it for about 2 months.

The way NetStumbler works is that it looks for "special" packets that have weak keys. Once it gets enough of these (a million is a good number) it can crack your WEP. The only problem with this is that the average home with one or two wireless connections would have to send constant data for months and months before there would be enough packets sniffed to crack it.

A business would do it in a week probably if they had say 25-50 wireless users, but 1-3 wireless connections wouldn't be enough data to even bother sniffing out.

Not like I know ANYTHING about doing this kind of stuff though....

Re:I have always had one or more of these wireless

[MrAndrews]

I actually found a conflict between the wireless phones and wifi to be rather widespread. At my house we had a problem where if you were closer to the base station with your laptop than the phone was to its base station, the phone wouldn't always ring --- and then if you were further away with the laptop the phone would drop your internet while it was ringing. Can't say I've checked out newer phones... we've switched to iChat AV and cell phones for all our telecommunications needs :)

Re:5.8

[Aaden42]

From: http://www.vocal.com/data_sheets/80211a_fre.html

The 5 GHz U-NII frequency bans is segmented into three 100 MHz bands for operation in the US. The lower band ranges from 5.15 -5.25 GHz, the middle band ranges from 5.25-5.35 GHz and the upper band ranges from 5.725-5.825 GHz.

So odds are a 5.8GHz phone would mess with the upper range of 802.11a.

Joining the 900 MHz crowd..

[cmowire]

The cordless phone manufacturers have been playing quite a game over the past decade. They keep trying to get you to upgrade phones to a "higher" megahertz phone because they know that you are already being told by Intel to upgrade your CPU to a "higher" megahertz CPU.

So, here's the thing. It's a general rule that as you go up in megahertz, the ability to penetrate walls goes down. Thus, the higher the megahertz, the lower the effective range. Consumer Reports did some tests here and showed that this carries over to reality. This is also why Verizon Wireless tends to have better reception -- they are primarily on the 850 MHz band instead of the 1900 MHz band.

So what have you gotten by upgrading to an "advanced" 2.4 or 5.8 GHz phone? Less range, although generally enough range to make it around a "normal" house.

Now, in order to produce a device that works in the 900 MHz, 2.4 GHz or 5.8 GHz band without a license the FCC requires you to be spread-spectrum.

There's some upsides and downsides here. First, some of the spread-spectrum devices, most notably older ones, didn't use very good spread-spectrum methods.

Second, in *theory* if everything's optimized properly, you can use some number of devices and they will all be perceived as "noise" to all of the other devices. So as you add more functioning devices in general, they will all start to experience interference. The problem is when devices using conflicting spread spectrum techniques are in use.

Third, microwaves and other such RF-heating applications, are covered underneath a different set of FCC rules, which generally are built around not causing your eyeballs to be fried overeasy (your eyeballs are the first thing to suffer damage from microwaves, which is why staring at the microwave window is not the world's brightest idea) Microwaves are supposed to be Faraday cages, but sometimes there's a leak. I'd start to wonder about my Microwave's safety if it started interfering with my WiFi, mind you.

Fourth, if there's interference and undesired performance, you have essentially no recourse. I've been thinking that they really should have allocated a frequency band that's reserved for only devices using a 802.11-standard protocol, but that decision really should have been made a long time ago. Oh, and if you start interfering with something important (That's the "Harmfull Interference" they speak of on the FCC warning on the back of a device) you can and will have government folks knocking on your doorstep. There have been documented cases of equipment interfering with aircraft navigation signals from the ground, which makes the airlines very unhappy and tends to get investigated. ;)

I'm really wondering what the "Wifi-Friendly" cordless phones are actually. Especially given that VTech is the folks who are advertising it. As I've mentioned above, in *theory* any device on the 900 MHz, 2.4 GHz, and 5.4/5.8 GHz ISM bands (they are actually the same thing) shouldn't prevent each other from working and should just be perceivable as noise Also, *in theory*, one could "do better" by listening for 802.11b/g activity and actively routing around it. This is the big difference between Bluetooth 1.1 and 1.2. But that's more circuitry, so I'm not entirely sure if they are actually doing that, or they just put them in a test lab to see what happens. They'll probably insist that it took years of engineering time and it's a special feature, even if it's more the second. ;)

I personally have just stuck to 900 MHz phones. Like I said, all things being equal, they tend to have longer range. Plus, I figure that having absolutely no interference is better than having a measured amount while the phone is in use. ;)

Sure my WiFi uses 802.11b, which is 2.4 GHz, but there's some darn good reasons for why one should keep 802.11a around.

The main one is that 802.11a is usually faster than 802.11g at close range. So I have a halfassed

Re:Joining the 900 MHz crowd..

[0111 1110]

Good post. I was going to mod you up, but I'd like to make a minor correction instead. As many have stated, the "penetration ability" of RF waves is inversely proportional to frequency (proportional to wavelength). For getting through building structures the best are 46/49 Mhz phones followed by 900, 2.4, and 5.8. What no one has (yet) mentioned is that higher frequencies do give better range for unobstructed line-of-sight transmission. Higher frequencies require less power (especially important for handsets) to propogate through empty space. The problem lies with obstructions like walls.

Anyone who has tried to use a handheld GPS while hiking in dense forest has seen that even 1227 or 1575 Mhz is a high enough frequency to have difficulty penetrating the leaves on trees (at least at such low power).

So as long as you can actually see your base a 5.8 Ghz cordless phone (RF transmitter) will give you the greatest range, but in any situation with obstructions it will give you the least range per unit of output power.

46 Mhz is such a low frequency that it penetrates walls easily without losing much power, but it is less efficient at open-space propogation (per watt). 900 Mhz seems to be a nearly perfect balance (perhaps 450 Mhz might be better). The frequency is high enough that open space propagation is very efficient, but still low enough that it will penetrate walls with some effectiveness.

Spread spectrum is not a form of "frequency hopping" in most cordless phones. It is a form of "wideband" transmission. It does not actually "hop" per se (although there are exceptions). It does allow for greater power and range. The longest range cordless phones for most people who live indoors in a multi-room house is a 900 Mhz spread spectrum phone.

I bought as many of these as I could because I knew that MarketSpeak would win over RF theory and that truly long range cordless phones would probably become unavailable.

Re:Joining the 900 MHz crowd..

[Anonymous Coward]

Almost correct. 1 watt is 1 watt at any frequency. Tell hams that lower frequencies won't carry as far but stand back if you don't want get get wet from the laughter you get back. What higher frequencies do is allow higher gain antennas with less space. The least, effective, antenna is 1/4 of the wavelength of the frequency (with ground plane) 1/2 without a ground. Frequecy goes up wavelength goes down. To make a 1/4 wave antenna at 49MHz you need over 4 feet. The same 1/4 wave antenna at 900MHz needs only 3/4 inch. 900 MHz is a very good balance for cordless phone. High enough frequency for small antennas, low enough to penetrate walls and such. Also the FCC allow greater power output at higher frequencies. 4 watts EIRP (1 watt into a 6db gain antenna) at 2.4GHz and 16 watts at 5.8 GHz. The requirements at 49MHz are much lower.

Re:5.8

[stilwebm]

The other question is, will the 5.8 interfere?

I have an AT&T 5840 phone that uses 5.8GHz but if you read the fine print in the specifications, it also uses 2.4GHz:

• RF Frequency Band (Handset to base): 2400 MHz - 2483.5 MHz
• RF Frequency Band (Base to handset): 5725 MHz - 5850 MHz

All 802.11b/g devices use channels within 2412 MHz - 2483.5 MHz, so there is quite a bit of overlap there. When shopping around, I noticed that many 5.8 GHz phones actually use 2.4 GHz as well. In my limited use of 802.11b in the vicinity of this phone, I noticed no interference, but ymmv.

Re:why 0.9Ghz is better

[bwalzer]

Free space loss for radio transmissions (in dB): L(f,d)=20.log(f*d)+92.5

...

So obviously L(2.4GHz,d) > L(0.9GHz,d). Meaning lower frequency leads to less loss (further reach).

Which is true, but misleading. Fascinating RF engineering trivia follows;

The variable L is often called "free space path loss". This sort of path loss increases with frequency. But where is the actual loss? This is supposed to be in free space, i.e. vacuum. Since there isn't anything in vacuum to heat up or whatever the loss can't be in the actual path between the antennas (which is why the "path loss" bit is misleading).

It's because of the antennas. An efficient omnidirectional transmitting antenna will radiate pretty much all the power you feed it. An omnidirectional receiving antenna will receive power proportional to it's size. Obviously larger antennas will collect more power. Rather than giving each antenna a separate transmit gain and receive gain the RF engineering types just fudge it with the idea of "free space path loss".

So yes, you will end up with more signal at the receive antenna of a 0.9GHz as opposed to a 2,4GHz phone. The formula is correct in that. After all the receive antenna is 2.7 times bigger. That's a whole 8 dB more signal. Of course the larger antenna will receive noise that much better too (and there tends to be a lot at 900MHz). The 900 MHz antenna will probably be so large that you will only be able to get one in a handset (some 900MHz phones actually have an extendable antenna). If the 2.4GHz faction puts more than one antenna in their handset and then has the phone pick the one with the best signal, they will probably win in practice.

Real path loss caused by things like building materials and trees does tend to go up with frequency. OTOH higher frequency signals can squeeze though smaller holes. It's all a bit complicated. I personally suspect that free space path loss isn't a significant factor in the actual range you end up with.

Re:900mhz?

[number11]

We're talking about cordless, not cellular. You furriners need to read for comprehension.

Some GSM cell phones run on the 900MHz band (880-960MHz).

Some US cordless phones run on the 902-928MHz band. But thanks for your insightful comment anyhow, AC.

Re:900mhz?

[badasscat]

We're talking about cordless, not cellular. You furriners need to read for comprehension.

Pot kettle black.

Someone apparently doesn't know that 900mhz cordless phones exist, and all of them are wi-fi friendly. I myself have a Panasonic 900mhz digital spread spectrum phone and have no problems at all with my wi-fi when using it.

Re:Why YES, I have had problems

[jht]

Interestingly, many of the 5.8 GHz phones (like the one I use at home, it's an AT&T) actually only receive from the base station at 5.8 GHz. In order to save on their power budget, they transmit back in the good old 2.4 GHz band.

Though they do play much nicer with 802.11x than older generation stuff did.

In general, I've seen that newer phones coexist nicely, and also 802.11g devices seem to be less interference-prone than 802.11b. Also, 900MHz phones play pretty nicely because they aren't even in the same neighborhood.

Re:5.8

[TWX]

"But the real question is, considering the speed and price of 802.11g these days, why would you ever choose to run 802.11a?"

Multiple reasons:

• Less people on it. Channels will be available until the end of time, and even if everyone in your neighbourhood has an access point, you won't have network problems.
• Less interest with wardrivers. While "security through obscurity" isn't the best idea if you're going to pick only one way to secure your systems, if you combine the fact that most people aren't looking for 802.11a networks with the fact that there are tons of open 802.11b and 802.11g networks you won't be looked upon as a potential victim nearly as much. It's not the end of security, but it's a good beginning.
• No protocol issues. 802.11b and 802.11g frequently have issues sharing, where the "g" features dumb down to "b" speeds if anything "b" is talking. This is bad in my opinion.
• Few, if any consumer devices in the 5GHz range. Nothing running in the house on 5GHz means nothing interfering with the network. Since everyone seems to be making 900MHz and 2.4GHz devices, including microwaves, telephones, and other things, using the currently lightly-used 5GHz area makes a lot of sense to me.

I was really sad that 802.11a never really made it to prime time in Linux while it was still commercially viable to manufacturers. I'd have bought into it in a heartbeat.