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2.4 to 2.4835 Ghz services
Occupy large part of the 12cm Amateur Radio Band 2400 - 2450Mhz
2.4 Ghz services: Video, Audio, Data and Telephone devices of domestic and commercial use. Even microwave ovens use this frequency for cooking by heating water at 2450Mhz, the frequency which water molecules (H2O) will vibrate at and heat up.
For most domestic communication gear (AV senders or data routers) typical distance is ~10 meters to100 meters (300feet) or more if using narrow-cast antenna, 2 dish like objects each with their own mast and pointed at each other. Typical domestic devices transmit at power levels of about 1mW to 10mW (max) and commercial devices like alarm sensors from ~1mW through to microwave ovens of 1000+ Watts and licensedradio amateurs are allowed 10's to 100's of watts.
The 2.4Ghz (2400Mhz) band can be very noisy and a hostile communication place, it is considered a 'public park' whereeveryone can use it and everyone has to put up with the interference from each other, users that try to abuseor dominate the frequency are eventually dealt with by the Media Authority. The 5.8 Ghz band is quieter, less crowded, also considered a 'public park' and has it own set of characteristics for communication activities.
2.4 Ghz Amateur TV is assigned these frequencies:
aTV1 assigned to: 2406-2424 Mhz (2415 -/+9Mhz bw for AM or FM) &
aTV2 assigned to: 2430-2448 Mhz (2439 +/-9Mhz bw for AM or FM)
CW & SSB
fm sstv rtty
|fm links to|
|.||.||.||Out of band|
or guard band
|--||2487 - 2497|
|WiFi type||Protocol||.||Freq Strt||Freq End||Data Rate||5.8GHZ|
DSSS = Direct Sequence Spread Spectrum
OFDM = Orthogonal Frequency Division Multiplexing
Bluetooth = a communications protocol used on 2.4Ghz
802.11x = a communications protocol used on 2.4 & 5.8Ghz
"Frequency Hopping" Allows more people to use this narrow part of the radio frequency spectrum by changing channels rapidly in predefined sequences. Thus allowing the "electronic smarts" to easily recover the audio / video / data information from what sounds like a hash of noise. Older video / audio systems show this noise as pulsating line interference or strong varying audio hiss.
Note: 2.4Ghz is considered a poor long distance (10's of km) terrestrial communication frequency due to the physics of water (vapour) absorption. Also as microwave ovens exploit this feature and operate at 1000's of Watts inside a metal box to heat food the noise in the band can be quite high. As more short range devices (1 to 250 meters) use this band, the interference level will become very high, to counter act this interference different modulation techniques and frequency hopping algorithms are used.Transmitter output power levels for each set of devices may add to the reception problems of other non-linking devices but with encoded signals turned on, polarised antenna (oriented horizontal or vertical) or physical separation of devices, operation and security from other users can be achieved.The other "public license" bands / frequencies that have similar uses for voice (phone) video (security) data (internet) are 700Mhz, 850Mhz, 900Mhz, 1.8Ghz, 5.8Ghz. Some of these bands are also used for mobile / cell phones, hence the ease of "Bluetooth" or wireless functionality with your other communication / multi-media devices.
|WiFi 2 GHz Channels|
Red out of bounds Ch.
If you can not get a clear channel: To limit interference & decoding delays, pick the same channel as the strongest signal. The wifi receivers can detect & reject signals not for them as they each slot-in their own carrier wave signals. As adjacent overlapping channels can not detect all carrier waves, they assume interference and need to resend data... The OFDM scheme of 20Mhz bandwidth occupies 4 x 5MHz channels, i.e. 1 below & 2 above the selected channel; ch.02, 06 & 10 or 2 below & 1 above: ch.03, 07 & 11. Effectively 13 channels (60MHz) allow 3 non-overlaping groups. The OFDM scheme of 40Mhz bandwidth occupies 8 x 5Mhz channels effectively accommodating one large group placed with-in 13 Channels. There is no set channel usage for either scheme, just a rule of thumb to apply and minimise interference. Everybody has their own idea of what is best for them and manufacturer defaults are not designed for minimum interference. Advanced WiFi users should scan the band and workout best channel to occupy and review when throughput becomes slower. Several smartphone apps can advise a less noiser channel to occupy, but this will change over time...
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Updated: 2016 Thu May.12
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