[Hidden-tech] Network-eating phone

[Jim Ussailis]

Here is the whole interference issue for the layman, and some reasons for 
it. Sorry it is so long.


"Portable" phones do not work at 2.2 GHz. There are several bands where 
cordless phones are legal. The "legal" part is a requirement because 
they are transmitters, and come under FCC "license free" rules.

Cell phones come under different FCC rules because they are licensed.

Cordless phones operate on about 46 MHz, 902 to 928 MHz, and 2400 to 2483 
MHz. In GHz terms, the last two bands are 0.9 GHz and 2.4 GHz.

1 GHz = 1000 MHz

We refer to these bands as: 

46 MHz = Cordless phone band (old technology, and not used much now)

902 - 928 MHz = 900 MHz band. Many mfgs make phones in this band,

2400 MHz - 2483 MHz = 2.45 GHz band. Many mfgs make phones in this band

So, you are stuck with the last two bands. In either of these bands you 
will find analog (voice), digital, and spread-spectrum phones. 

Analog gives you NO security whatsoever. Power is regulated to a small 
amount, so range is limited.

Digital gives you some security. Power is also regulated to the same as 
analog.

Spread-spectrum comes in two flavors, which are important. allowable 
power is vastly greater, so range and interference fighting is better, 
but interference to other services is greater. Spread-spectrum offers 
good security.

Flavors: Frequency hopping. Immune from some interference, Can cause 
interference.

Direct-sequence. Immune from most interference. Can cause some 
interference. Unfortunally 802.11 b/g devices use the same form of 
spread-spectrum. BUT these devices cannot talk to the phone (and 
vice-versa) unless they use exactly the same code.

The 900 MHz band has lots of users, not as many as a few years ago, tho. 
In it you will find cordless phones, and wireless gadgets like cordless 
headphomes, the Rabbit (a tv transmitter), my mini wireless TV camera, 
and some remote control devices. I believe the Bose remote control is in 
this band.

The 2.45 band started as a home for microwave ovens. They radiate a lot 
of junk, which causes interference, more so for frequency hopping, less 
so for direct-sequence. Many other gadgets operate in this band, 
including 802.11 b/g lan devices, Bluetooth, and Zigbee devices.

If you want a reasonable shot at clear phone signals, go with a 
direct-sequence 900 MHz phone. IBM did make one that works just fine, I 
got mine from BJs. This phone will probably not interfere with WiFi, or 
any operations in the 2.45 band.


Jim Ussailis

jim at nationalwireless.com


PS Be careful about some so-called "long range" phones out there. They 
operate in an amateur radio band. They are not legal, and the FCC has 
begun to enforce their removal. There is an interesting case of a Pizza 
place that refused to act on the FCC letter. I believe their fine was 
either 8K or 10K.