Re: 4 . Wireless alarm systems INTERFERING sources>

[-pull@shoot]

On Thu, 05 May 2005 01:33:21 +0200, -pull@shoot wrote:

>
>What type of signals are able to produce RFI (Radio Frequency
>Interference) on Wireless Alarm Systems and will jeopardize they're
>operation?
>
>Not all Radio Frequency (RF) transmitters are able to generate RFI,
>they have to be in accordance to certain rules described hereafter.
> Find here with more detail the list of Radio Frequency (RF)
>transmitter sources generating RFI mentioned here above:
>
>1. RF transmitters operating "ON" the Wireless Alarm Systems
>   frequency.
>   This is the most annoying RFI, it require only a very low power to
>   do so (in my REAL case, 1 milliWatt was enough);
>
>2. RF transmitters "SATURATING" the input stage of the Wireless Alarm
>   Systems RF receiver
>   A transmitter "close" to the operating frequency may have enough
>   power to saturate the RF receiver input stage.
>   This signal overrides the normal incoming RF sensor signals.
>   This can happen with permanent installed RF transmitter stations or
>   temporary operated (CB, Radio Ham, ++) mobile or fix.
>
>3. RF transmitters causing "INTERMODULATION"
>   "In gross" its the mix of two signals that result in an on
>   the frequency signal of the Wireless Alarm Systems due to the
>   non-linearity of wireless RF receiver input stage.
>   It can be defined as a beat tone generated by two signals where
>   the mixed beat part is on the Wireless Alarm operating frequency.
>   Realize that quite a fair amount of combinations may produce
>   that sort of RF signal.
>
>4. "HARMONICS" of a RF transmitters falling in the Wireless receiver
>   frequency bandwidth.
>   All transmitters generate harmonics, those harmonics have to
>   be suppressed (EMC requirement) to a certain degree,
>   nevertheless there are still attenuated harmonics and when you
>   have to deal with a powerful RF transmitter they may still be
>   sufficient to "muzzle" the RF receiver sensor inputs of the
>   Wireless Alarm Systems.
>
>5. a RF transmitter signal not directly on the frequency who is "NOT
>   ATTENUATED" enough by the RF "receiver bandpass filters".
>   The RF receiver's use already since approx. 20 years SAW filters.
>   Those filters attenuate the beside the frequency incoming signals,
>   however those signals are still coming true in an attenuated manner
>   but they may be of a sufficient amplitude to "interfere" the RF
>   receiver sensor inputs.
>
>6. RF transmitters on the IF (intermediate frequency)
>   Modern wireless receivers use frequency conversion techniques
>   who uses and IF stage to narrow the bandwidth (easier on lower
>   frequencies).
>   One drawback with them, if the IF frequency is not attenuated
>   enough by the input stage, a RF transmission on that frequency will
>   pass and generate RFI.
>
>As you see there is a quite some impressive number possible of RF
>transmitter sources that may generate RFI on Wireless Alarm System
>receivers.
> The major problem being that specific RFI avoidance techniques, used
>in military and by similar instances, are not affordable for wireless
>alarm systems even if the FCC (or like instances) would allow this
>type of avoidance techniques in wireless alarm systems.
>
> RFI is expectedly most of the time (and lucky enough) of the
>involuntary nature and not persistent but in the meanwhile the system
>is deaf and when it comes to security realize how easy it is to have a
>Wireless Alarm Systems disturbed... dead.
> Silent key, NO ALARM, NO DETECTION.
>
>Paul