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UER Forum > Archived UE Encyclopedia > CB (Viewed 115 times)
Kenshin 


Location: Eagan, MN
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CB
< on 1/24/2004 11:45 PM >
Posted on Forum: UER Forum
 
Short for Citizen's Band Radio. CB range in frequency from 26.965 to 27.405 mHz in 40 channels and is limited to 4 watts ERP. This is the predecessor for the FRS (Family Radio Service). Being the Citizen's band, a license is not required to broadcast. Applications are mostly limited to vehicles, however hand held units can be bought as well. Because CB is required to broadcast on AM, it does not work well when in an urban area. Buidlings and obstacles get in the way of transmission. CBs are also subject to a phenomana called skip in which broadcasts are bounced off the ionosphere, typically at night. It is not uncommon to hear transmissions from Mexico and Canada because of this. Because of the power limit, transmission radius of a CB is significantly higher then that of the FRS. On a decent day, CB transmission can be as far as 5 miles clearly and 10 miles not so clearly whereas the FRS rated at .5 of a watt can only transmit to a maximum of 2 miles typically.


Edit by ExKa|iBuR:

Correction: CB Radios are limited to 4 watts input to the antenna stage. You can have (in theory anyway), as much ERP as you'd like. ERP doesn't refer to how much power you're actually transmitting, rather what the EFFECTIVE power output is. Example: You could transmit 10 watts into a unity (zero) gain antenna, and have 10 watts ERP. You could take that same 10 watts and put it into a 3db gain antenna, and you'd have 20 watts ERP. For every 3db of gain, your ERP is increased on a logirithmic scale by 2. So, if you have a large beam antenna with say, 20db of gain, your 4 watts would seem like 80 watts.

This 4 watts is in AM (Amplitude Modulation). CB radio is also permitted to use SSB (Single Side-Band) in which you are allowed 12 watts out. The difference is that AM has a continuous carrier, and you are always transmitting 4 watts. With SSB, there is no carrier. It's difficult to transmit 12 watts, as the more audio you push into the radio, the higher your output power is. This is why you always see SSB operators with gain mics and are usually talking rather loudly.

Edit by spRocket:
Note that there is a tradeoff in gain (and thus, ERP) versus directionality. A high-gain antenna will be highly directional, whereas a unity gain antenna is omnidirectional.

-Ex
[last edit 1/24/2004 11:45 PM by Crispy Critter - edited 2 times]

UER Forum > Archived UE Encyclopedia > CB (Viewed 115 times)



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