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

Why YES, I have had problems

[johncel]

So, I had a linksys wifi router and an AT&T 2.4 gHz phone... They fought like dogs! If the phone rang, wifi was out for at least 5 mins after you hung up. What a pain. I finally just bought a 5.8 gHz phone.

It doesn't interfere, silly

[Anonymous Coward]

It interoperates. If it finds an open port on your wifi network, it will handover and use VoIP to complete the call.

This saves you money in the long run because VoIP is much cheaper cost-wise than typical cell service.

The main thing is to make sure that the phone is SAR-approved. You don't want those microwaves heating up your neural tissue! :-)

Are they nuts?!

[Pan T. Hose]

24GHz?! Who the hell would need such a fast phone is beyond me! I have a 500MHz AMD in my desktop (Debian) and it works just fine, thank you.

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:why 0.9Ghz is better

[CMRichar]

i think you forgot:

6)are inexpensive.

I know that

[Pan T. Hose]

24GHz?! Who the hell would need such a fast phone is beyond me! I have a 500MHz AMD in my desktop (Debian) and it works just fine, thank you.

ARE YOU NUTS? Obviously they left out a dot on the frequency. The frequency your phone transmits on has nothing to do with speed like a processor. Get out of here.....

I know there are other important speed-wise factors as well, the most important one being not the clock frequency itself but whether the chip has 64 bits or not. Nevertheless, I don't think anyone would ever need more than 640MHz.

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..

[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:My microwave

[Smurf]

No more skull-to-the-microwave-window pressing for me either.

Uhh... but you DO press your skull against the phone handset, which allegedly transmits a stronger signal (at least at that frequency)...

May I recommend a tin foil hat? ;)

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.