Microwave and Vonage

Posts: 47 · Posted: Wed Mar 23, 2005 10:25 pm Post subject: Microwave and Vonage

Hello,

We have a cordless phone system that we use with our PAP2 Vonage adaptor. When we had the cordless phone system connected into wall jacks using SBC no problem with interference from Microwave. Now if we stand by our Microwave while talking on the phone we get terrible interference and can't continue with the call!? Not a big deal, however find it kind of weird! Just curious if anyone else has had this happen?

Thanks

Posts: 183 · Posted: Wed Mar 23, 2005 10:58 pm Post subject:

I'm guessing here, but it sounds like you might be using a 2.4 GHz wired base station and wireless expansion handsets. If you have your wired base plugged into your TA elsewhere in the house and use a wireless handset near the microwave you will be subject to interference from the microwave since it too works in the 2.4 GHz frequency. It is causing RF noise along with your signal to the base station. The ideal solution is to upgrade to a 5.8 GHz phone system, or not use the telephone while standing near near the microwave when it is on.

Hope this helps. My conversion to an AT&T 5800 phone system fixed the problem for me right away, less of course about $200 in my bank!

Posts: 47 · Posted: Thu Mar 24, 2005 7:19 am Post subject: Thanks!

Thank you for taking the time to post an explanation!

Posts: 42 · Posted: Sun Mar 27, 2005 1:14 am Post subject:

Your microwave probably lists the nominal frequency that it uses. Ours operate at 2450MHz, right smack in the middle of the 2.4GHz ISM (Industrial/Scientific/Medical) range. The microwave is pumping a few hundred watts of energy in electromagnetic wave form into your food. In theory the shielding keeps it inside, but some always leaks.

Suppose there is 500W of energy inside the cabinet, and a 0.1% leakage rate. That is 0.5 watts of 2.4GHz noise leaking into your house. (500 milliwatts). This is just an example, I dont know for sure what typical levels are, but I can guess.

Wifi and cordless phones run their transmitters in the milliwatt range. 802.11b devices transmit typically in the 30-50 milliwatt range, and max out at 200 milliwatts.

Anyway, for some strange reason, the blast of 2.4GHz noise leaking from the microwave totally swamps other uses of the 2.4GHz ISM band.

"Blast" is probably the wrong word. The signal levels we are talking about are really really small. The microwave oven leakage is tiny, but wifi and cordless phones run on much smaller levels still. After all, nobody wants to put any more microwave energy into people's skulls than absolutely possible these days for fear of lawsuits.

The good news is that microwave ovens tend to not use the entire ISM band. Most of the energy is right in the middle and the noise levels drop dramatically as you move away from the center frequency. So while you are up really close, even the smaller off-center frequencies can disturb your phone or wireless, but once you get away from it a bit, the phones can usually change channels to avoid the worst of the interference.

How the phone system copes, depends on its design and radio system. Some phones use spread spectrum style signalling, others use narrow frequency slots and change channels as needed (frequency hopping). The design of the radio electronics is significant too. If the tuner is not very selective, the tuner can let in lots of the nearby frequency noise from the microwave and swamp the radio, causing it to turn down the amplification gain. Imagine that two people are shouting next to your ear, loud enough to hurt. You put your hands over your ears. And now for some reason you can't hear the other voice you're trying to listen to.

Switching to 5.8GHz avoids this problem, for a while. It too is an unlicensed spectrum, and it will become crowded over time, especially with all the 2.4GHz refugees heading over there.

The other problem with 5.8GHz is that it penetrates walls etc much more poorly than 2.4GHz. Thus signal problems are likely to be much more of an issue. However, there are several other factors too.. Firstly, the poor signal penetration of 5.8GHz means you're less likely to pick up stray background 5.8GHz noise from your neighbors phones or the 802.11a system etc. This works in your favour. Secondly, the radios and air interface designs are generally quite superior to older 2.4GHz and 900MHz designs. The chances are fairly good that your 5.8GHz phones can work much more satisfactorily on a poor signal strength.

Also, newer cordless phone designs came after the 802.11 boom, so they've learned that they need to listen specifically for 802.11 beacons and packets, not for continuous low level background noise like they'd expect from a microwave oven. That's what they mean by "802.11 friendly".

Anyway, that's probably more than you ever wanted to know. Smile

BTW: was the cordless phone base station physically in the same location when it was plugged into the SBC jack as it is now? If you moved the base station for some reason, I'm guessing there is a different proximity to the microwave oven somehow. For example, if the base station used to be in the kitchen at the SBC phone jack, and now it is elsewhere else in the house, near a broadband connection, all of a sudden the signal levels between the kitchen and base station are much lower than before and the microwave will drown it out much more easily.