Re: 15. Wired / Wireless alarm systems?

["Softy" <jimveal001@xxxxxxxxx>]

Hmmm,

Almost correct. You have negated to mention 2-way wireless systems where
both the panel and the detection devices are both transmitters & receivers.
RFI jamming is correctly detected and the better systems only report jamming
when it knows that a detector signal has been jammed. How does it know?
Simple, the panel expects a message from the detectors every nth period
defined in the wireless protocol used. If jamming is reported and the panel
is armed, the panel can behave accordingly. What about a random detector
activation?. Easy, because the system is 2-way all activations by the
detectors require an acknowledgement from the panel. If the detector does
not get an acknowledgement it sends the signal again...and again either
until an acknowledgement is received or until the jamming period is reached.
Once this period has been reached the detector can shut down safe in the
knowledge that the panel will now report jamming. In short, if any detector
activation signal is lost the panel can report jamming.

You are correct though when you mention that wired is more reliable than
wireless. Always will be the case. No argument. However 2-way wireless
systems do provide a reasonable bridge between wired (longer to install,
cheaper & very reliable) and uni-directional wireless (easier to install,
more expensive & not as reliable).

Have fun


<-pull@shoot> wrote in message
news:p6la91hmmjldg5mvebccqk3kspfcfgis4l@xxxxxxxxxx
>
> 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
>