Recording of a channel-bonded 802.11n network set up in the 5 GHz band on Wi-Fi channels 44 and 48. "11n" creates a signature that looks much like two 802.11g signals that are exactly side-by-side--with steep sides and a flat top. Since it is 40 MHz wide, and occupies two 5 GHz channels (or 6 channels when deployed in the 2.4 GHz band!), much care must be taken to spread out these networks to practice proper spectrum management. Also, Wi-Fi interference from neighboring "11n" networks can be common because such a wide swath of spectrum is taken up by them.
 

This recording demonstrates proper channel placement on Wi-Fi channels 1,6 and 11 with 802.11b/g networks. Since there are only 3 channels (or 4 in Europe and Japan) that do not overlap, a spectrum that looks like this is desirable for avoiding the creation of co-channel interference when deploying many access points or WLANs in an area. For an example of a poorly chosen Wi-Fi channel scheme--and it's effects--see the recording titled "Lotsa Wi-Fi!"
 

A close-up recording of a very active 802.11g network on Wi-Fi channel 6. When 11g is in an active state of download or upload it develops a squarish silhouette with a flat top--much like the profile of a desert mesa. Also, because this access point is transmitting a lot of data and is creating a lot of RF energy, the side "shoulders" bleed off across the entire 2.4 GHz band.
 

Wi-Fi anarchy! Well, not quite but access points on every available channel does cause chaos in the spectrum because of the overlap. And, since beacons are sent out constantly from the APs, there is constant noise and throughput rates are negatively affected on all APs. A perfect example of what-not-to-do.
 

The bane of the 2.4 and 5 GHz bands, the old-school non-frequency hopping cordless phone puts out a constant (high duty-cycle) signal when in use. Even though they are only on for a few minutes at a time (the length of an average phone call) cordless phones are a common and ubiquitous source of interference in WLANs and cause slowness and general frustration for network admins everywhere. Usually identified by their 'spike-like' signature, cordless phone interference can occur on just about any Wi-Fi channel and some models change frequency each time a call is made.
 

Bluetooth is frequency-hopping and spread spectrum, so it doesn't stay on one frequency for long and it does have some 'noise avoiding' channel choosing features built into it. But, with that being said, Bluetooth does cause interference with WLANs especially when many Bluetooth devices are transmitting in one area. The following recording is a scan of 14 Bluetooth high-range devices sending 1 image every 14 seconds. Bluetooth creates a signature that can span the entire 2.4 GHz band and is recognized by individually narrow (1 MHz-wide) silhouettes.
 

There is rarely a workplace or residence that does not have at least one microwave oven on site. And, since most companies or households are not willing to go without them, there is usually no choice but to avoid them rather than eliminate them.
Microwaves generate a silhouette that is more random and "mound-shaped" than a defined signature that emits from data-transmitting electronic devices. Depending on the model, it's age or what's being cooked in it, microwaves can emit RF noise on any of the Wi-Fi channels and can be relatively wide or narrow.
 

Recording of a Samsung wireless home speaker system affecting Wi-Fi channel 1. Audio transmitters like this one can be very constant and be quite loud and need to be accounted for when deploying a WLAN. Thoughtful Wi-Fi channel placement with devices like these in the wireless landscape is imperative for wireless co-existence.
 

Recording of a wireless video camera affecting the 2.4 GHz band. Wireless cameras are commonly used for security as well as for purposes such as inventory management. So, these devices might not be physically visible or generally discoverable--and in many cases--cause 'mystery' interference to 2.4 GHz networks. Most A/V transmitters produce a loud, constant signal and many produce a 'triple-peaked' signature.
 

Almost as ubiquitous as the microwave oven, 2.4 GHz cordless phones are inexpensive, plentiful and are used frequently throughout the day. Much like 5 GHz phones, they ususally emit a narrow, steep-sided signature and can jump around on different frequencies every time a call is made. What's worse, the 2.4 GHz band is smaller, so cordless phones have more potential to cause interference. Only recently have manufacturers begun to market "non-interfering" phones (i.e. 1.9 GHz DECT), so cordless phone interference will continue to be a major issue for Wi-Fi for the foreseeable future.