Re: 15. Wired / Wireless alarm systems?

[-pull@shoot]

On Thu, 26 May 2005 06:48:46 +0200, -pull@shoot wrote:

>
>Why are wired alarm systems more reliable than wireless alarm system?
>
>What is the basic difference between wired and wireless alarm systems?
>
> It boils down to the "connections link" between sensors and control
>panel of both systems, besides that sensor data connection link both
>systems are alike.
>
>So the comparison is easy, the WIRED WIRES versus a WIRELESS data link
>between sensors and the control panel.
>
>WIRED:
>- Each sensor has "hiss own" cabling, hiss own data transmission link.
> All attempts to tamper sensor boxes, short or cut sensor wires are
>detected without any ambiguity an with no delay.
>
>- At a first glance the wired links are of the non-frequency selective
>type and as such are more prone to capture a greater Radio Frequency
>(RF) spectrum range of signals.
> The data transmitted on sensor wired lines are of the low frequency
>type and as such can easily be filtered at all inputs entering the
>control panel.
> This makes the system data link low frequency selective by
>attenuating the eventual High Frequencies reaching the equipment by
>huge power transmitters.
>
>- The level of the transmitted signals on the wired lines are around
>"2Volt" to switch from on to off (to be more precise, 400mV
>interference free immunity for TTL circuits).
>
>WIRELESS:
>- All the sensor data is vehicle via ONE wireless data link composed
>of a low power transmitter in the sensors and a sensitive receiver at
>the input who has around 4 microvolt input sensitivity (wired 400
>millivolt (mV) / wireless 4 microvolt (uV) = ratio 100 000 times less
>power required to disturb wireless systems)
>
>- The wireless data link contains all the information required to have
>a reliable connection as long as there are no other transmissions
>present who block the data communication.
> The wireless RF receiver collect in normal circumstances the data and
>decode it. This data contains an ID (rolling code), alarm, tamper
>attempt, battery low and more information. When the signal is
>disturbed, EVERYTHING is, ID can't be recognized...
>
>The receiver:
>  The receiver is made as much as possible frequency selective and
>sensitive at signals on the frequency in order to capture the week
>signals emanating from the sensors (see below).
> They "attenuate" more or less, depending on the quality of the
>receiver, the frequencies beside that privileged frequency, its called
>the bandpass attenuation range (essential quality comparison data not
>provided and published by the manufacturers in order to mask how bad
>the bandpass is).
>
>The sensor transmitters:
>  In wireless alarm systems the transmitting power is limited by law
>and by reasonable battery live time.
>  The RF transmitter power of the sensors is of the order of 10
>milliwatt (mW), low, very low.
>
>COMPARISON:
>- The receive end is 100,000 times more sensitive to signals in
>wireless versus wired (4uV / 400mV);
> The ratio is even higher because the high frequencies, where
>disturbing transmissions occurs, are attenuated by low pass filters at
>the input of the wired lines.
>
>- The link in wired systems are wires who can be filtered/shielded
>against RF interferences (and by location of the wires); in wireless
>it is the open air reachable by everybody, no shielding possible.
>
>CONCLUSION:
>- An external RF transmitter can disturb both systems but the power
>required to do this is much higher in wired systems (>100,000 times).
>- In wireless systems, the power required to interfere and disturb the
>system is similar to the sensor power (10mW) when generated at the
>same distance, RFI power should be increased if the distance is
>increased.
>- Wireless alarm systems are not reliable, they can be interfered and
>disturbed/muzzled due too and by an outside transmission.
>
>FINAL NOTE:
>- Don't forget that in order to interfere wireless alarm systems that
>the RF disturbing signal source should satisfy some frequency
>requirements.
> For example; cell phones with theyre 2 watt power don't satisfy that
>frequency dependent requirement and as such don't disturb normally.
>
>Paul