Dumb question re 2.4GHz wireless frequency

[Ken90630]

I assume this has prolly been asked before, but since I'm more or less a newb at wireless networking, here goes:

As I understand it, wireless routers typically use the 2.4GHz frequency band. So, I think, do most cordless phones, right? Do they or can they conflict with each other? If so, what are the symptoms? And when setting up a wireless router & network in a home where the users are already using 2.4GHz cordless phones, what (if anything) should be done to prevent problems?

 

[spidey07]

You are correct as well as microwave ovens. It depends on the phones but most are spread spectrum which means they hop all over the usable frequency range. They are considered a source of interference.

To mitigate this keep the phone base station as far away as you can from the access point and try channels 1, 6, 11 on the AP to see what works best. If the phone has an antenna point the AP antenna straight up and down and the phone antenna horizontally.

 

[Ken90630]

Thanks for the info. By "access point," you're referring to a wireless router, right?

Another question: If a cordless phone is near a wireless router, but the phone is just sitting in the "cradle" in the base and isn't actually on (i.e., it's not making or receiving a call), is there still a potential prob with interference? Or does the intereference only occur when a call is being made or received?

While I'm at it: If, hypothetically, a microwave oven is turned on and it happens to be in a wireless router's signal path, are you saying that signal could be degraded or interfered with?

 

[spidey07]

The wireless phones are constantly using the spectrum at all times. If the microwave oven is in the path and in use then it's a HUGE amount of noise, enough to render a wifi signal essentially unusable.

The fact remains - these are all sources of interference/noise. how much it impacts what you are trying to do depends on your environment.

 

[QuixoticOne]

Originally posted by: Ken90630
Thanks for the info. By "access point," you're referring to a wireless router, right?

Another question: If a cordless phone is near a wireless router, but the phone is just sitting in the "cradle" in the base and isn't actually on (i.e., it's not making or receiving a call), is there still a potential prob with interference? Or does the intereference only occur when a call is being made or received?

While I'm at it: If, hypothetically, a microwave oven is turned on and it happens to be in a wireless router's signal path, are you saying that signal could be degraded or interfered with?

1) Phone in base -- well it depends. Some base stations use RF to communicate a little bit with the handsets even when there is not a call present. This would more often be the case when you have multiple handsets since while each handset has its own 'charging base' there is only one (typically) base that actually has a phone landline attached to it and which communicates with the remote handsets / bases. Generally speaking if the handset is right next to the 'main' base the signal will be strong enough that wireless router interference will at best make the connection a bit more noisy but won't prevent it from being usable. If you had a handset way out at the limits of its range and it was also relatively nearer to some wireless access points then you'd see more serious effects of the interference in terms of noise and limited usable range.

2) Microwave ovens are kept inside metal boxes that keep the RF inside the box. There are regulations and standards and construction practices that tend to ensure that the energy of RF that comes out of the ovens into the room is far less strong than the signal put out by a decent wireless NIC / access point. Also microwave ovens operate in a relatively narrow range of frequencies so they'd tend to at most cause interference in a few "micro channels" but any spread spectrum type phone / NIC would really not be bothered too much by the narrowband low power RF leakage from microwave ovens.

 

[Ken90630]

Thanks a lot, guys. :beer:

I prolly should have clarified one thing a little better: I'm more concerned with how cordless phones (using 2.4GHz) might adversely affect a wireless router's signal strength/integrity than I am with how the router might affect the phones. The latter matters as well, but it's of secondary importance.

I recently had some trouble setting up a wireless home network for some friends, and I couldn't quite determine, with certainty anyway, why the wireless signal strength was so poor about 50' away from the router (which supposedly puts out a strong signal good for up to 100'). There are several walls and other barriers to the signal, so that's definitely an issue, but I'm wondering if their cordless phones are contributing to the problem as well. Based on what you guys are saying, it could be -- particularly since the phone charging base is about 6' away from the router and the phone sits in that cradle most of the time.

 

[ChAoTiCpInOy]

Anyone know what channel is the best one to use?

 

[spidey07]

Originally posted by: ChAoTiCpInOy
Anyone know what channel is the best one to use?

The one that gives you the highest signal to noise ratio for your environment.

Oh and what I mean is it can change with every second.

 

[spidey07]

Originally posted by: QuixoticOne

Originally posted by: Ken90630
Thanks for the info. By "access point," you're referring to a wireless router, right?

Another question: If a cordless phone is near a wireless router, but the phone is just sitting in the "cradle" in the base and isn't actually on (i.e., it's not making or receiving a call), is there still a potential prob with interference? Or does the intereference only occur when a call is being made or received?

While I'm at it: If, hypothetically, a microwave oven is turned on and it happens to be in a wireless router's signal path, are you saying that signal could be degraded or interfered with?

1) Phone in base -- well it depends. Some base stations use RF to communicate a little bit with the handsets even when there is not a call present. This would more often be the case when you have multiple handsets since while each handset has its own 'charging base' there is only one (typically) base that actually has a phone landline attached to it and which communicates with the remote handsets / bases. Generally speaking if the handset is right next to the 'main' base the signal will be strong enough that wireless router interference will at best make the connection a bit more noisy but won't prevent it from being usable. If you had a handset way out at the limits of its range and it was also relatively nearer to some wireless access points then you'd see more serious effects of the interference in terms of noise and limited usable range.

2) Microwave ovens are kept inside metal boxes that keep the RF inside the box. There are regulations and standards and construction practices that tend to ensure that the energy of RF that comes out of the ovens into the room is far less strong than the signal put out by a decent wireless NIC / access point. Also microwave ovens operate in a relatively narrow range of frequencies so they'd tend to at most cause interference in a few "micro channels" but any spread spectrum type phone / NIC would really not be bothered too much by the narrowband low power RF leakage from microwave ovens.

That's fine in theory, not so in practice. Microwave ovens reak havoc in the 2.4 spectrum.

fire up a spectrum analyzer and see what they spew and the energy they radiate. I don't just make up crap I post or reguritate what somebody else read on the internet. It's a very real problem.

 

[ScottMac]

For 802.11g (and b) channels 1, 6, and 11 are the only real choices.

Each of the listed channels (1...11 in the USA) are the center of a 5MHz stripe of the spectrum. Unfortunately, the width of the stripe used is 25MHz wide (five "channels").

So, if you are on channel 1, the next channel that can be used without mutual interference is 6, then 11 (5 stripes apart).

If someone chooses channel 2, 3, or 4, they will interfere (and be interfered by) the next 2 adjacent channels in both directions.

SO, the usual "best practice" for potentially congested areas is to download and run Netstumbler (www.netstumbler.com), and see what the activity level is in your neighborhood, and pick the least-congested channel (out of 1, 6, or 11).

You should also check every so often because new APs are lighting up all the time.

802.11a (5.6G) has 40 non-overlapping channels, and is much less used ... so if you have a dual AP/router and a dual freq NIC, use 802.11a for your stuff at home and 802.11g when "you have to." (I use 802.11g at home for Airport Express connections to the machine running iTunes, for example).

Good Luck

Scott

 

[cmetz]

Ken90630, 802.11(DS/FH, b, g, a, n et al) uses spread-spectrum techniques to avoid point noise sources. Really dumb phones that only operate on exactly one center frequency can just be avoided thanks to this. Many cordless phones also use a basic spread spectrum technique or have a horribly wide bandwidth, so they wipe out an entire 802.11 "channel" - which can be avoided by changing the channel on your AP/client device. Usually between the spread spectrum and changing the channels you can coexist on the same band without too much trouble - that is after all the FCC's requirement for the band!

Occasionally, though, you'll find a cordless phone that's just toxic to the 2.4GHz band and wipes out pretty much everything, think a badly implemented spread spectrum with a really wide bandwidth too. The solution to those is to throw them away, or to get 5GHz networking gear (802.11a or 5GHz n). Usually it's cheaper to replace the phone, because usually we're talking about a cheapo phone if it's misbehaving in that way.

Also keep in mind that there are some good quality 900MHz, 1900MHz, and 5GHz band cordless phones. So if you replace your cordless phones with ones that just don't even work in the 2.4GHz band, that source of problem just goes away. For example, if you go buy a new cordless phone (or cordless phone "system") that uses DECT, that's on the 1900MHz band.

 

[Ken90630]

Thanks again, guys. I really appreciate the info and education. :beer: