Best of the ISP-Lists

Interfering Cordless Phones

Members of the ISP-Wireless list discuss a new fear for fixed wireless broadband operators: Interference from 2.4 GHz cordless phones. It's rare but possible.

[April 27, 2001]

On the ISP-Wireless list in April, JT asked,

"I have now had two different people tell me 2.4GHz is not usable in Reno, Nevada, because there are too many cordless phones being used. One company said they pulled all their 2.4GHz stuff because they could no longer get a good threshold. Could this be true? I need to know before I start flushing money down the toilet."

A number of respondents were pretty skeptical about the possibility:

[CE offered] "Sounds to me like someone who is trying to keep out competition. I think you'd have heard plenty of horror stories all around the country already if it were true."

[MC recalled] "I've tested my system against various cordless phones. While I interfere with the phone, I cannot find any reverse interference. If you look at the specs on the phones, they don't have much output. Since all of our gear are on high gain antennas running back to central WiPoPs, the math looks good too."

[MS agreed] "2.4GHz phones are a total non-issue."

Others noted that there might well be a problem with 2.4GHz RF:

[RB observed] "Our local county government has been using it for about three years. There have been some problems with interference on the south side of town."

[MS agreed] "Downtown Spokane, Washington is full of 2.4GHz RF. I've found that people often all try the same thing, and they all fail in the same way. Find out where the others had their systems, and put yours somewhere else. It's mostly an issue of design."

PL explained that it's really about cheap, poorly-made phones:

"There are many different types of 2.4GHz phones. The good ones use the guard bands on either side of our spectrum, one side to transmit and the other to receive. These phones stay out of our hair. The cheaper 2.4GHz phones fast hop throughout the band. These can have impact on some systems, especially indoor WLANs. It's hard to tell which phone is which on the surface. Don't bother to call their customer service; they won't know. Maybe if your customers sign a one-year contract, you can throw in a free 900MHz phone..."

—End

Related articles:
	[Aug,. 21, 2000]	Another Kind of Unlicensed RF
	[Feb. 6, 2001]	Competing Wireless Technologies