Re: 7. An overview of wireless alarm system techniques (part 2 of 2)..

[-pull@shoot]

On Thu, 05 May 2005 17:28:13 +0200, -pull@shoot wrote:

>
>In order to avoid confusions i like to approach some "hidden" FCC
>requirements.
> Why hidden?
> Because they are not apparent (?) but unavoidable during the
>manufacturer design phase.
> So lets try to go on that hidden part ----> certification of the
>designed equipment...
> It's a manufacturer concern but you have to know what is exactly
>involved with that, in order to avoid confusions generated smoke by
>some so called professionals (?).
>
>Before i can handle that i need to give some context information.
>
>Receiver types (simplified):
>Regenerative, single and double conversion maybe used. All have in
>some sense small "transmitters" build in due to the principle in the
>case of the super regenerative type or due to the oscillator in the
>other types.
>The transmitted signal generated is the unwanted radiated part of the
>receiver system and must be suppressed below a certain level in order
>not to disturb other equipments in the vicinity.
>
>uC Processors (simplified):
>At the actual state of art it's easy to use a micro-controllers to do
>the required functions in the sensors and at the control panel.
>Those micro-controllers (or similar devices) use a clock. Clocks
>operate on a frequency and are as such a small transmitter.
>Here again that unwanted radiated signal must be suppressed below a
>certain level.
>
>Regions:
>The world is divided in regions having each they're own regulations.
> Region 1 (part): In the European community you have EU regulations
>that are individually integrated in the different member states.
>Region 3 (part): The US, Canada, ++ are in that region.
>Let's keep it like that, it's incomplete but sufficient for the
>explanation.
>Regulations in those regions are close to each other but with some
>small(?) differences between each other subject certification
>requirement (and frequencies assigned to wireless systems).
>The differences have no real impact on what will be stated hereafter.
>
>ElectroMagnetic Compatibility of the equipment's:
> ElectroMagnetic Compatibility (EMC) is a requirement.
> A lot can be said about EMC but it's in fact a requirement that tend
>to keep compatibility between different equipment's using electronic
>circuits inside.
> It specify for all types of equipment (not only wireless system but
>also dishwashers and + using uP's):
>- the maximum limit of internal generated "unwanted" signals
>- the minimum of un-sensitivity (required to avoid "unwanted" radiated
>   signals form other equipment's) to disturb the operation.
>The difference between unwanted transmissions and un-sensitivity is
>called to be the immunity margin, the first being lower than the
>second of course.
>
>Transmitter regulation:
>Complex specifications that measure in essence side bands, harmonics,
>and frequency stability.. to mention only a few.
>
>Wanted versus unwanted signals:
>Note the big difference between "wanted" an "unwanted" signal.
> The transmitted frequency in a transmitter is "wanted" signal, the
>emissions generated by the other internal electronic circuits are
>"unwanted".
> In a receiver the wanted signal is the receive frequency of the
>wireless alarm system, the unwanted all the others (oscillators).
>
>General concept of certification:
>It's the proof that the equipment satisfies the regulations.
>Each design has to undergo test in open air or in an open air like
>environment, called anechoic chamber (++).
>Most of the time open-air measurements are not allowed for evident
>possible disturbances to the environmental area.
>Specialized and authority agreed body's are allowed to produce a
>certification.
>In some specific cases, the manufacturer may certify by themselves
>hiss equipment.
>Note that the test and measurement equipment's used to do the
>certification must be certified to (in hiss domain).
>
>I like to mention, in order to avoid confusions, that those tests are
>standard requirements for all equipment's (from dishwasher to..) and
>have nothing to do with the specific concept of a wireless alarm
>system.
>
>The above was only a scratch of reality but had the intent to mention
>that a design has to undergo general certification tests.
>Its wise to take in account that hidden requirement during design
>because when the certification limits are exceeded its difficult to
>resolve them latter on (additional shielding, filtering, ++).
>
>Paul