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| Re: Canarsie CBTC (99529) | |||
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Thu Jun 16 09:44:50 2005, in response to Re: Canarsie CBTC, posted by tracksionmotor on Wed Jun 15 22:47:28 2005. Don't talk RF propagation to me...the 'sticker box RF comm system' that NYCTA will use is like the cheapo RF TV remotes....and subject under law to any and ALL interference as an unlicensed part 15 user. That's right...NYCTA will use an unlicensed Part 15 system on ungaurdedfrequencies. Say I key up on 440 mHz FM with five watts and second harmonic of ELP level coincides with trainset comm links. Something happens, trainset comm system huntsa for another frequency (IF system works that way) with dead comm BIE trainset. Whos fault is it? NYCTA, trainset manufacturer, vendor or me? On any frequency at any time of any mode of any power level, I am the primary user as licensed by the FCC as a commercial radio operator. TA/trainsets...just cheap CB. Clearly, a receiver is badly designed, if a legal signal can overpower the its RF or IF stages. This has not proven to be a problem for the more than 15 million 802.11 spread spectrum systems currently in use in the US. Spread spectrum is not like most of the RF applications that you have encountered with regard to its suseptibility to RF interference. It is used by the military for battlefield communications because it is far less likely to be jammed or have its security compromised than most other forms of RF communications. Spread spectrum systems operate reliably in the presence of more powerful wide and narrow band signals even when there is spectral overlap. Those are the properties of the type of RF link that is planned for CBTC. The best (or worst depending on one's perspective) jamming signal is not necessarily a strong one. It is one that mimics the characteristics of the desired signal. Something about correlation detection and Wiener filtering. That's why AC powerline arcing gives spread spectrum problems. Primary, legal use of the assigned frequencies by radio amateurs should not. |
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