Guest
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 Posted:
Mon May 30, 2005 12:36 am Post subject:
22. Who call that junk Spread spectrum in Wireless Alarm Sys |
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Regardless of some that try to flood the fish by mentioning unrealized
performances of spread spectrum (SS) in wireless alarm systems,
regardless the invalid comparisons with military equipment, everybody
knows that wireless alarm systems are unreliable during Radio
Frequency Interference (RFI).
WHY?
Does that Spread Spectrum (SS) do any good to interferences avoidance?
Yes, of course "IF" it is applied the correct way like in military /
space / ++ equipment's ($$$).
What's the correct way to implement spread spectrum?
1. The hopped frequencies should be "wide spread" over different
frequencies, each frequency acting likes a separate transmitter /
receiver link operating on a whole different frequency.
2. The receiver should be tuned to each frequency in a "synchronous"
manner with the transmitter otherwise it will capture even better
RFI due to hiss wide spread capture range required when the
receiver is not hopped.
3. The receiver should be small band and receive only the requested
hopped frequency and not capture at once the whole range of spread
frequencies.
First:
How can the required synchronized transmission between sensor and
control panel workout with "multi-sensor transmitters" operating
"asynchronously" as required use in Wireless Alarm Systems?
Impossible or with a high-speed multi frequency switching receiver,
too expensive for the application here, to $$$.
Second:
FCC (and other country authorities) regs only allow spread-spectrum
use on three bands: 902-928 MHz, 2.4 GHz, and 5.8 GHz. Those bands are
not available for wireless alarm systems.
3 th:
Some systems implement small frequency hopping (very limited spread
spectrum) feature, WHY do they let believe to sales people that there
is SS in theyre system?
Wireless Alarm Systems don't use the spread spectrum possibility as it
should be in order to avoid interferences, they're allocated frequency
spectrum is to restricted and the receiver is only tuned to the center
frequency of the hopped frequencies (the large bandwidth cope with all
hopped frequencies and as such is even more interference sensitive).
The design purpose of this erroneously mentioned so called SS feature
is to avoid sensor location black spot problems inherent to the higher
frequencies used and not to avoid RFI like some tend to let you
believe.
Propagation problems and sensor location:
The frequency hopping used in some wireless alarm systems is used to
resolve the sensor propagation nodes problems at the receiver end when
a metal objects is displaced from his initial installation setup
position (car, statue, ++).
Conclusion on SS frequency hopping:
Why does installer and maintenance persons think (say) that it they
have better systems now?
Because they have the impression that they have a more solid (better)
wireless data link connection in normal operating conditions because
they find it not so critical by initial sensor position setup.
That limited frequency feature, that manufacturers and sales people
tend to let you believe as the latest miracle, is worse than more
selective receivers designed to capturer one frequency.
The wide receiver range included in so called SS systems capture all
hopped frequencies simultaneously and as such open an even wider RFI
susceptibility door.
Again, where are the manufacturer technical specifications about the
wireless data loop involved in theyre system???? Embarrassing to show
to the general public the low quality of they're equipment in that
area.
Wireless alarm systems are UN RELIABLE during interference and don't
warn you when they are MUZZLED.
Paul
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Guest
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| Posted:
Sat Jul 02, 2005 2:30 pm Post subject:
Re: 22. Who call that junk Spread spectrum in Wireless Alarm |
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On Mon, 30 May 2005 02:08:40 +0200, -pull@shoot wrote:
| Quote: | Regardless of some that try to flood the fish by mentioning unrealized
performances of spread spectrum (SS) in wireless alarm systems,
regardless the invalid comparisons with military equipment, everybody
knows that wireless alarm systems are unreliable during Radio
Frequency Interference (RFI).
WHY?
Does that Spread Spectrum (SS) do any good to interferences avoidance?
Yes, of course "IF" it is applied the correct way like in military /
space / ++ equipment's ($$$).
What's the correct way to implement spread spectrum?
1. The hopped frequencies should be "wide spread" over different
frequencies, each frequency acting likes a separate transmitter /
receiver link operating on a whole different frequency.
2. The receiver should be tuned to each frequency in a "synchronous"
manner with the transmitter otherwise it will capture even better
RFI due to hiss wide spread capture range required when the
receiver is not hopped.
3. The receiver should be small band and receive only the requested
hopped frequency and not capture at once the whole range of spread
frequencies.
First:
How can the required synchronized transmission between sensor and
control panel workout with "multi-sensor transmitters" operating
"asynchronously" as required use in Wireless Alarm Systems?
Impossible or with a high-speed multi frequency switching receiver,
too expensive for the application here, to $$$.
Second:
FCC (and other country authorities) regs only allow spread-spectrum
use on three bands: 902-928 MHz, 2.4 GHz, and 5.8 GHz. Those bands are
not available for wireless alarm systems.
3 th:
Some systems implement small frequency hopping (very limited spread
spectrum) feature, WHY do they let believe to sales people that there
is SS in theyre system?
Wireless Alarm Systems don't use the spread spectrum possibility as it
should be in order to avoid interferences, they're allocated frequency
spectrum is to restricted and the receiver is only tuned to the center
frequency of the hopped frequencies (the large bandwidth cope with all
hopped frequencies and as such is even more interference sensitive).
The design purpose of this erroneously mentioned so called SS feature
is to avoid sensor location black spot problems inherent to the higher
frequencies used and not to avoid RFI like some tend to let you
believe.
Propagation problems and sensor location:
The frequency hopping used in some wireless alarm systems is used to
resolve the sensor propagation nodes problems at the receiver end when
a metal objects is displaced from his initial installation setup
position (car, statue, ++).
Conclusion on SS frequency hopping:
Why does installer and maintenance persons think (say) that it they
have better systems now?
Because they have the impression that they have a more solid (better)
wireless data link connection in normal operating conditions because
they find it not so critical by initial sensor position setup.
That limited frequency feature, that manufacturers and sales people
tend to let you believe as the latest miracle, is worse than more
selective receivers designed to capturer one frequency.
The wide receiver range included in so called SS systems capture all
hopped frequencies simultaneously and as such open an even wider RFI
susceptibility door.
Again, where are the manufacturer technical specifications about the
wireless data loop involved in theyre system???? Embarrassing to show
to the general public the low quality of they're equipment in that
area.
Wireless alarm systems are UN RELIABLE during interference and don't
warn you when they are MUZZLED.
Paul |
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