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| Re: Canarsie CBTC/RF (99842) | |||
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Re: Canarsie CBTC/RF |
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Posted by Jeff H. on Fri Jun 17 02:41:40 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Thu Jun 16 09:44:50 2005. Stephen,He's talking about "front end overloading", a widely-understood problem in RF communications. Even when spread-spectrum is used, as in 802.11, it is still a relatively narrow band. E.g. 802.11b and g are between 2.412 and 2.462 GHz. I'm pretty sure most designs have one RF amp for that entire band, and then do the frequency-hopping on the receive side by changing local oscillator frequencies. If you can get enough RF energy within that band delivered to the antenna, it will either drive the RF amp into clipping, or the AGC will kick in and reduce the amplitude of the real signal that is being delivered to the IF stage. Obviously you can design around that by using very good shielding, and having large dynamic range in the RF circuits. But it is certainly possible. I have seen commerical-grade 802.11 systems degrade and even fail to associate with the AP from proximity to strong RF sources, or even a large amount of aggregrate RF energy, e.g. when too many people are running their own private 802.11 networks in close quarters. |
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