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

[-pull@shoot]

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