View Full Version : RFI: Radio Frequency Interference

04-08-08, 09:08 PM
Here's one for the books: We all hear about RFI in and from TV's, cell phones, remotes, and radar. How about between a cordless telephone and a wireless access point ?? As in: home network.

The upstairs PC is fed by a LAN Ethernet line connected to an encrypted Linksys Router, which is hard connected to a Verizon DSL dedicated landline. The "roaming" laptop uses an encrypted wireless link to the ^^ Linksys, good for all over the house and yard.

On the upstairs work desk is a Radio Shack cordless phone/answering machine, fed from the other landline number. (Other cordless and hardwired phones are in other locations on the same line also.)

When the telephone rings, the upstairs Radio Shack cordless kills the wireless signal from the router. Dead. (No other phone does this.) My laptop tries to lock onto some distant non-secure access point 1,200 feet from here. Hang up the RS handset and shift to any other phone, all's well: laptop locks back onto the encrypted Linksys signal.

What's the workaround ?? ......other than killing the RS phone/answering machine ??

04-08-08, 10:22 PM
The phone appears to be hogging the same spectrum of the 2.4GHz band as the router. The first thing I would recommend is to access your wireless router's configuration page and choose a DIFFERENT communication channel (most routers allow either automatic frequency hopping or static/manual channel selection). The second option is relocating EITHER the RS phone OR the Wireless base station however possible. If neither of those work, and they may not since both devices have strong enough transmitters to reach a good 300ft radius at minimum and may "bleed" into other channels, you'll need to kill the phone or try a different router.

You think that's weird? My Mircrowave knocks out ALL bluetooth communication within 30 feet. DEAD.

04-08-08, 11:29 PM
I fought the router vs. phone war for longer than I care to admit. Phones are available in more frequency flavors than wireless routers so I bought a phone setup that operates in a different frequency world altogether.

04-09-08, 08:22 AM
The 2.4GHz frequency used by wireless routers is unlicensed.

It is sometime shared by bluetooth, garage door openers, cordless phones and a load of other gadgets.

What you describe is all too common.

I'd suggest replacing either ht ephone with one that uses a different frequency or better yet switch to an "n" wireless router that can use the 5GHz frequency.

04-09-08, 10:55 AM
Part of the reason cordless phones started coming out in 5.8 gig and the newest DECT 6.0.

04-09-08, 01:54 PM
I have a similar setup and it works fine. Do you have the DSL filters installed on all of your phone jacks in use?

04-09-08, 02:29 PM
I have a similar setup and it works fine. Do you have the DSL filters installed on all of your phone jacks in use?

It doesn't have anything to do with the actual phone line itself, rather the wireless band which most wireless routers and cordless phones both occupy - the 2.4GHz.

Jim - you have a few different options... but first, what sort of wireless protocol are you running... 802.11G or the older 802.11B? The older "B" protocol was notorious for getting fouled up by 2.4GHz phones... It was said that "G" was to largely solve the problem, but has some caveats.

Most fairly recent routers are set to run in "compatibility" mode, which operates on both b/g... if your laptop is running wireless-G, you could try setting it to G-only and assigning a specific channel. I also don't know what's offered on the Windows-side, but the Mac has a feature called "Interference Robustness" or something like that... I found that switching over to G-only and enabling that setting eliminated any lockouts of my wireless signal.

Your other options include (if capable) the ancient 802.11A protocol, but you'll loose speed and your system and/or router may not be capable of such, but it operated on a different frequency. You could upgrade to the new wireless-N draft, which claims higher throughput on a higher 5.8GHz frequency... but the speed claims are highly theoretical as wireless-G already exceeds the bandwidth of most consumer broadband connections... not only that, but it's expensive proposition as you would have to get a new router and a wireless-N pc card, and that's only if your laptop has an expansion slot.

The cheapest and most hassle free solution? Run out to Radio Shack/Best Buy/Walmart and buy a ten dollar 900MHz cordless phone... that way you're not spending much money and you don't have to bother sifting though a bunch of mundane submenus in your network settings and router... especially the router because I absolutely loathe Linksys - I'm actually surprised it even works for you, I've never had such luck with them.

I'll only buy Motorola, as they actually make IMO the best built, most reliable routers that I've come across... D-Link and Apple's Airport tie for second. I'm actually using an Airport now simply because we had an extra one at work that came with one of our mobile MacBook labs that we weren't using... but I wouldn't actually buy one just because Apple is the BMW of computer manufacturers - somethings you're definitely paying for the badge. But I think the Moto one we bought after our D-Link crapped out was only like 30 bucks online, and it's never missed a beat... but I digress...

But yeah, just go buy a cheap 900MHz cordless phone... it'll save you a lot of headaches!

04-09-08, 03:00 PM
Like I said, I have a similar setup. wired LAN and wireless 802.11B access point. I have 900mhz and 2.4Ghz phones and I have laptops running 802.11G and PDAs using the 802.11B protocol. My system works fine. The filter was a suggestion. The Radio Shack phone signal might be drifting

04-09-08, 03:44 PM
Thanks for the feedback.......now we're good to go: As in Cadillacs, when all else fails, read the instructions. Both electronics are on almost the exact same freq, so I fooled with different channels on the router, no luck. Moved the phone to another location, better but not 100%. Took advice of several posters and went to RS a couple of hours ago and bought an el cheapo 900 mHz phone/answering machine. BINGO ! (I don't need DSL inline filters because that line is dedicated to the computer only, runs straight to the DSL box from outside, and is unlisted/unpublished. The home phone is a completely separate number/line.)